Biochemistry is the study of the
chemicalChemistry is the science concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical reactions...
processes in living
organismIn biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
s. It deals with the
structureStructure is a fundamental and sometimes intangible notion covering the recognition, observation, nature, and stability of patterns and relationships of entities...
and function of cellular components such as
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s,
carbohydrateCarbohydrates
[Means "hydrates of carbon"] or saccharides
[The word comes from the Greek σάκχαρον, sákcharon, meaning "sugar").] are the most abundant of the four major classes of biomolecules...
s,
lipidLipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others...
s,
nucleic acidA nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid and ribonucleic acid . Nucleic acids are universal in living things, as...
s and other
biomoleculeA biomolecule is any organic molecule that is produced by a living organism, including large polymeric molecules such as proteins, polysaccharides, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products.As organic molecules,...
s.
Among the vast number of different biomolecules, many are complex and large molecules (called
polymerA polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties.Due to the extraordinary...
s), which are composed of similar repeating subunits (called
monomerA monomer is a small molecule that may become chemically bonded to other monomers to form a polymer...
s). Each class of polymeric biomolecule has a different set of subunit types. For example, a
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
is a polymer whose subunits are selected from a set of 20 or more
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
s. Biochemistry studies the chemical properties of important biological molecules, like proteins, and in particular the chemistry of
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at...
-
catalyzedCatalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate...
reactionA chemical reaction is a process that leads to the transformation of one set of chemical substances to another. They are studied by chemists under a field of science called chemistry. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about...
s.
The biochemistry of
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
metabolismMetabolism is the set of chemical reactions that occur in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter,...
and the
endocrine systemThe endocrine system is a system of glands that involve the release of extracellular signaling molecules known as hormones.The endocrine system is instrumental in regulating metabolism, growth, development, puberty, tissue function, internal environment and also plays a part in determining...
has been extensively described. Other areas of biochemistry include the
genetic codeThe genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells. A more precise term for the concept might be "genetic cipher". The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids...
(
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
,
RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
),
protein synthesis,
cell membraneThe cell membrane is the biological membrane separating the interior of a cell from the outside environment....
transportIn cellular biology the term membrane transport refers to the collection of mechanisms that regulate the passage of solutes such as ions and small molecules through biological membranes namely lipid bilayers that contain proteins embedded in them...
, and
signal transductionIn biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another. Most processes of signal transduction involve ordered sequences of biochemical reactions inside the cell, which are carried out by enzymes and activated by second messengers,...
.
Since all known life forms that are still alive today are descended from one of two
common ancestorA group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool....
s, they have generally similar biochemistries.
It remains unknown whether alternative types of biochemistries are possible, or practical, given the
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
s composing the
matterThe term matter traditionally refers to the substance that all objects are made of. One common way to identify this "substance" is through its physical properties; a common definition of matter is anything that has mass and occupies a volume...
of the
UniverseThe Universe comprises everything that physically exists, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them...
. An emerging thesis, called "
carbon chauvinismCarbon chauvinism is a relatively new term meant to disparage the assumption that extraterrestrial life will resemble life on Earth. In particular, it would be applied to those who assume that the molecules responsible for the chemical processes of life must be constructed primarily from carbon...
," holds that only carbon-based compounds are available to be part of a real biochemistry.
History
Originally, it was generally believed that life was not subject to the laws of science the way non-life was. It was thought that only living beings could produce the molecules of life (from other, previously existing biomolecules). Then, in 1828,
Friedrich WöhlerFriedrich Wöhler was a German chemist, best-known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, nowadays a district of Frankfurt am Main...
published a paper on the synthesis of
ureaUrea or carbamide is an organic compound with the chemical formula
2CO. The molecule has two amine residues joined by a carbonyl functional group....
, proving that
organicOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
compounds can be created artificially.
The dawn of biochemistry may have been the discovery of the first enzyme,
diastaseA diastase is any one of a group of enzymes which catalyses the breakdown of starch into maltose. Alpha amylase degrades starch to a mixture of the disaccharide maltose, the trisaccharide maltotriose, which contains three α -linked glucose residues, and oligosaccharides known as dextrins that...
(today called
amylaseAn amylase is an enzyme that breaks starch down into sugar. Amylase is present in human saliva, where it begins the chemical process of digestion. Foods that contain much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns some of their...
), in 1833 by
Anselme PayenAnselme Payen was a French chemist known for discovering the enzyme diastase, and the carbohydrate cellulose.Payen was born in Paris...
.
Eduard BuchnerEduard Buchner was a German chemist and zymologist, the winner of the 1907 Nobel Prize in Chemistry for his work on fermentation.-Early years:...
contributed the first demonstration of a complex biochemical process outside of a cell in 1896:
alcoholic fermentationEthanol fermentation is a biological process in which sugars such as glucose, fructose, and sucrose are converted into cellular energy and thereby produce ethanol and carbon dioxide as metabolic waste products....
in cell extracts of yeast. Although the term “biochemistry” seems to have been first used in 1882, it is generally accepted that the formal coinage of biochemistry occurred in 1903 by
Carl NeubergCarl Alexander Neuberg was an early pioneer in biochemistry, and often referred to as the "Father of Biochemistry".He was the first editor of the journal Biochemische Zeitschrift. This journal was founded in 1906 and is now known as the FEBS Journal. Neuberg was born in Hanover, Germany and...
, a German
chemistA chemist is a scientist trained in the science of chemistry. Chemists study the composition of matter and its properties such as density, acidity, size and shape. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component...
. Previously, this area would have been referred to as
physiological chemistryPhysiological chemistry is the chemistry of the organs and tissues of the body and of the various physiological processes incident to life. Physiological chemistry is essentially the precursor to modern biochemistry. In the nineteenth century, physiological chemistry dealt primarily with...
. Since then, biochemistry has advanced, especially since the mid-20th century, with the development of new techniques such as
chromatographyChromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
, X-ray diffraction,
dual polarisation interferometryDual polarisation interferometry is an analytical technique that can probe molecular scale layers adsorbed to the surface of a waveguide by using the evanescent wave of a laser beam confined to the waveguide...
,
NMR spectroscopyProtein nuclear magnetic resonance spectroscopy is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins. The field was pioneered by, among others, Kurt Wüthrich, who shared the Nobel Prize in Chemistry in 2002...
, radioisotopic labeling,
electron microscopyAn electron microscope is a type of microscope, a scientific instrument which is used to magnify things on a fine scale. That uses a particle beam of electrons to illuminate a specimen and create a highly-magnified image...
and
molecular dynamicsMolecular dynamics is a form of computer simulation in which atoms and molecules are allowed to interact for a period of time by approximations of known physics,...
simulations. These techniques allowed for the discovery and detailed analysis of many molecules and
metabolic pathway-Cellular respiration:Several distinct but linked metabolic pathways are used by cells to transfer the energy released by breakdown of fuel molecules to ATP...
s of the
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
, such as
glycolysisGlycolysis is the metabolic pathway that converts glucose, C
6H
12O
6, into pyruvate, C
3H
6O
3-...
and the Krebs cycle (citric acid cycle).
Another significant historic event in biochemistry is the discovery of the
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
and its role in the transfer of information in the cell. This part of biochemistry is often called
molecular biologyMolecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
. In the 1950s,
James D. WatsonJames Dewey Watson, born April 6, 1928, in Chicago, Illinois, is an American molecular biologist, best known as one of the two co-discoverers of the structure of DNA, with Francis Crick in 1953...
,
Francis CrickFrancis Harry Compton Crick OM FRS , was a British molecular biologist, physicist, and neuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule in 1953, together with James D. Watson. He, James D...
,
Rosalind FranklinRosalind Elsie Franklin was an English biophysicist, physicist, chemist, biologist and X-ray crystallographer who made contributions to the understanding of the fine molecular structures of DNA, RNA, viruses, coal and graphite. Franklin is best known for her work on the X-ray diffraction images of...
, and
Maurice WilkinsMaurice Hugh Frederick Wilkins CBE FRS was an English molecular biologist, and Nobel Laureate who contributed research in the fields of phosphorescence, radar, isotope separation, and X-ray diffraction. He was most widely known for his work at King's College London on the structure of DNA...
were instrumental in solving DNA structure and suggesting its relationship with genetic transfer of information. In 1958, George Beadle and Edward Tatum received the
Nobel PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
for work in fungi showing that one gene produces one enzyme. In 1988,
Colin PitchforkColin Pitchfork was the first criminal convicted of murder based on DNA fingerprinting evidence, and the first to be caught as a result of mass DNA screening. Pitchfork raped and murdered two girls, the first in Narborough, Leicestershire, on November 21, 1983, and the second in Enderby, also in...
was the first person convicted of murder with
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
evidence, which led to growth of forensic science. More recently, Andrew Z. Fire and Craig C. Mello received the 2006 Nobel Prize for discovering the role of
RNA interferenceRNA interference is a system within living cells that helps to control which genes are active and how active they are. Two types of small RNA molecules – microRNA and small interfering RNA – are central to RNA interference...
(
RNAiRNAI is a non-coding RNA that is an antisense repressor of the replication of some E. coli plasmids, including ColE1. Plasmid replication is usually initiated by RNAII, which acts as a primer by binding to its template DNA. The complementary RNAI binds RNAII prohibiting it from its initiation role...
), in the silencing of gene expression
Today, there are three main types of biochemistry. Plant biochemistry involves the study of the biochemistry of autotrophic organisms such as
photosynthesisPhotosynthesis is a process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of Bacteria, but not in Archaea...
and other plant specific biochemical processes. General
biochemistryBiochemistry is the study of the chemical processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
encompasses both plant and animal biochemistry. Human/medical/medicinal biochemistry focuses on the biochemistry of humans and medical illnesses.
Monomers and Polymers
Monomers and polymers are a structural basis in which the four main macromolecules (carbohydrates, lipids, proteins, and nucleic acids), or biopolymers, of biochemistry are based on.
Monomers are smaller micromolecules that are put together to make macromolecules.
Polymers are those macromolecules that are created when monomers are synthesized together. When they are synthesized, the two molecules undergo a process called dehydration synthesis.
Carbohydrates
Carbohydrates have monomers called monosaccharides. Some of these
monosaccharides include
glucoseGlucose , a monosaccharide also known as - grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate...
(C
6H
12O
6),
fructoseFructose is a simple monosaccharide found in many foods. It is a white solid that dissolves readily in water. Honey, tree fruits, berries, melons, and some root vegetables, contain significant amounts of the fructose derivative sucrose...
(C
6H
12O
6), and
deoxyriboseDeoxyribose, also known as
D-Deoxyribose and 2-deoxyribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group in its linear structure...
(C
5H
10O
4). When two monosaccharides undergo dehydration synthesis, water is produced, as two
hydrogen atomA hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force. The most abundant isotope, hydrogen-1, protium, or light hydrogen, contains no...
s and one
oxygen atomOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
are lost from the two monosaccharides'
carboxyl groupA carboxyl group is a set of four atoms bonded together and present in carboxylic acids, including amino acids. Usually abbreviated as either CO2H or COOH, this set of atoms constitutes a functional group. In every carboxyl group the carbon atom is attached to an oxygen atom by a...
.
Lipids
Lipids are usually made up of a molecule of
glycerolGlycerol is an organic compound, also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. ...
and other molecules. In triglycerides, or the main lipid, there is one molecule of glycerol, and three fatty acids. Fatty acids are considered the monomer in that case, and could be saturated or unsaturated.
Lipids, especially phospholipids, are also used in different pharmaceutical products, either as co-solubilisers e.g. in
ParenteralParenteral is a route of administration that involves piercing the skin or mucous membrane. Parenteral nutrition refers to providing nutrition via the veins.-Etymology:...
infusions or else as drug carrier components (e.g. in a
LiposomeA liposome is a tiny bubble , made out of the same material as a cell membrane. Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases....
or
TransfersomeTransfersome is a term registered as a trademark by the German company IDEA AG, and used by it to refer to its proprietary drug delivery technology. The name means “carrying body”, and is derived from the Latin word 'transferre', meaning ‘to carry across’, and the Greek word ‘soma’, for a ‘body’...
).
Proteins
Proteins are macro biopolymers, and have monomers of
amino acids. There are 20
standard amino acidsProteinogenic amino acids are those 22 amino acids that are found in proteins and that are coded for in the standard genetic code. Proteinogenic literally means protein building...
, and they contain a
carboxyl groupA carboxyl group is a set of four atoms bonded together and present in carboxylic acids, including amino acids. Usually abbreviated as either CO2H or COOH, this set of atoms constitutes a functional group. In every carboxyl group the carbon atom is attached to an oxygen atom by a...
, an amino group, and a side chain (or an "R" group). The "R" group is what makes each amino acid different, and the properties of the side chains greatly influence the overall three-dimensional confirmation of a protein. When Amino acids combine, they form a special bond called a
peptide bondA peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water . This is a dehydration synthesis reaction, and usually occursbetween amino acids...
, and become a
polypeptide, or a protein.
Nucleic Acids
Nucleic acids are very important in biochemistry, as they are what make up DNA, something all cellular organism use to store their genetic information. The most common nucleic acids are deoxyribonucleic acid and ribonucleic acid. Their monomers are called nucleotides. The most common nucleotides are called
adenineAdenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
,
cytosineCytosine is one of the four main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
,
guanineGuanine is one of the five main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, thymine, and uracil. In DNA, guanine is paired with cytosine. With the formula C
5H
5N
5O, guanine is a derivative of purine, consisting of a fused...
,
thymineThymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine always pairs with adenine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be...
, and
uracilUracil is a common and naturally occurring pyrimidine derivative. Originally discovered in 1900, it was isolated by hydrolysis of yeast nuclein that was found in bovine thymus and spleen, herring sperm, and wheat germ...
. Adenine binds with thymine and uracil, thymine only binds with adenine. Cytosine and guanine can only bind with each other.
Carbohydrates
The function of carbohydrates includes energy storage and providing structure.
SugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
s are carbohydrates, but not all carbohydrates are sugars. There are more carbohydrates on Earth than any other known type of biomolecule; they are used to store energy and genetic information, as well as play important roles in cell to cell interactions and communications.
Monosaccharides
The simplest type of carbohydrate is a
monosaccharideMonosaccharides are the most basic unit of carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose and ribose...
, which among other properties contains carbon,
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
, and
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
, mostly in a ratio of 1:2:1 (generalized formula C
nH
2nO
n, where
n is at least 3).
GlucoseGlucose , a monosaccharide also known as - grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate...
, one of the most important carbohydrates, is an example of a monosaccharide. So is
fructoseFructose is a simple monosaccharide found in many foods. It is a white solid that dissolves readily in water. Honey, tree fruits, berries, melons, and some root vegetables, contain significant amounts of the fructose derivative sucrose...
, the sugar that gives
fruitThe term fruit has different meanings dependent on context, and the term is not synonymous in food preparation and biology. Fruits are the means by which flowering plants disseminate seeds, and the presence of seeds indicates that a structure is most likely a fruit, though not all seeds come from...
s their sweet taste. Some carbohydrates (especially after
condensationA condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule. When this small molecule is water, it is known as a dehydration reaction; other possible small molecules lost are hydrogen chloride,...
to oligo- and polysaccharides) contain less carbon relative to H and O, which still are present in 2:1 (H:O) ratio. Monosaccharides can be grouped into aldoses (having an
aldehydeAn aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double-bonded to an oxygen atom , is called the aldehyde group...
group at the end of the chain, e. g. glucose) and ketoses (having a
ketoIn organic chemistry, a ketone is a type of compound that features a carbonyl group bonded to two other carbon atoms, i.e., R3CCO-CR3 where R can be a variety of atoms and groups of atoms...
group in their chain; e. g. fructose). Both aldoses and ketoses occur in an
equilibriumIn a chemical process, chemical equilibrium is the state in which the chemical activities or concentrations of the reactants and products have no net change over time. Usually, this would be the state that results when the forward chemical process proceeds at the same rate as their reverse reaction...
between the open-chain forms and (starting with chain lengths of C4) cyclic forms. These are generated by bond formation between one of the hydroxyl groups of the sugar chain with the carbon of the aldehyde or keto group to form a
hemiacetalHemiacetals and hemiketals are compounds of the general formula R1R'1COR2, where R2 is not hydrogen. These types of compounds are formed from carbonyl compounds and alcohols, i.e. hemiacetals from aldehydes, hemiketals from ketones...
bond. This leads to saturated five-membered (in furanoses) or six-membered (in pyranoses) heterocyclic rings containing one O as heteroatom.
Disaccharides
Two monosaccharides can be joined together using dehydration synthesis, in which a hydrogen atom is removed from the end of one molecule and a
hydroxylIn chemistry, hydroxyl is composed of molecules consisting of an oxygen atom and a hydrogen atom connected by a covalent bond . The neutral form is a hydroxyl radical. The hydroxyl anion is called hydroxide; it is a diatomic ion with a charge of negative one...
group (—OH) is removed from the other; the remaining residues are then attached at the sites from which the atoms were removed. The H—OH or H
2O is then released as a molecule of
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
, hence the term
dehydration. The new molecule, consisting of two monosaccharides, is called a
disaccharideA disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only...
and is conjoined together by a glycosidic or ether bond. The reverse reaction can also occur, using a molecule of water to split up a disaccharide and break the glycosidic bond; this is termed
hydrolysisHydrolysis is a chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions, which may go on to participate in further reactions. It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization...
. The most well-known disaccharide is
sucroseSucrose, commonly called table sugar, is a moosaccharide of glucose and fructose with the molecular formula C12H22O11. This white, odorless, crystalline powder has a pleasing, sweet taste. It is best known for its role in human nutrition...
, ordinary
sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
(in scientific contexts, called
table sugar or
cane sugar to differentiate it from other sugars). Sucrose consists of a glucose molecule and a fructose molecule joined together. Another important disaccharide is
lactoseLactose is a sugar that is found most notably in milk. Lactose makes up around 2–8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey...
, consisting of a glucose molecule and a
galactoseGalactose is a type of sugar which is less sweet than glucose. It is considered a nutritive sweetener because it has food energy. Its name comes from the Ancient Greek word for milk, γάλακτος ....
molecule. As most humans age, the production of
lactaseLactase , a part of the β-galactosidase family of enzymes, is a glycoside hydrolase involved in the hydrolysis of the disaccharide lactose into constituent galactose and glucose monomers...
, the enzyme that hydrolyzes lactose back into glucose and galactose, typically decreases. This results in lactase deficiency, also called
lactose intolerance.
Sugar polymers are characterised by having reducing or non-reducing ends. A reducing end of a carbohydrate is a carbon atom which can be in equilibrium with the open-chain
aldehydeAn aldehyde is an organic compound containing a terminal carbonyl group. This functional group, which consists of a carbon atom bonded to a hydrogen atom and double-bonded to an oxygen atom , is called the aldehyde group...
or keto form. If the joining of monomers takes place at such a carbon atom, the free hydroxy group of the
pyranosePyranose is a collective term for carbohydrates which have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. The name derives from its similarity to the oxygen heterocycle pyran...
or
furanoseA furanose is a simple sugar that contains a five-membered furan-based ring structure and is a sub-terminal ketone which gives it reducing power.-Structural properties:...
form is exchanged with an OH-side chain of another sugar, yielding a full
acetalAn acetal is a molecule with two single bonded oxygens attached to the same carbon atom.Traditional usages distinguish ketal from acetal...
. This prevents opening of the chain to the aldehyde or keto form and renders the modified residue non-reducing. Lactose contains a reducing end at its glucose moiety, whereas the galactose moiety form a full acetal with the C4-OH group of glucose. Saccharose does not have a reducing end because of full acetal formation between the aldehyde carbon of glucose (C1) and the keto carbon of fructose (C2).
Oligosaccharides and polysaccharides
When a few (around three to six) monosaccharides are joined together, it is called an
oligosaccharideAn oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars. The name is derived from the Greek word oligos, meaning "a few", and from the Latin/Greek word sacchar which means "sugar"...
(
oligo- meaning "few"). These molecules tend to be used as markers and signals, as well as having some other uses. Many monosaccharides joined together make a
polysaccharidePolysaccharides are polymeric carbohydrate structures, formed of repeating units joined together by glycosidic bonds. These structures are often linear, but may contain various degrees of branching. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit...
. They can be joined together in one long linear chain, or they may be branched. Two of the most common polysaccharides are
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
and
glycogenGlycogen is the molecule that functions as the secondary long-term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by glycogenesis within the brain and stomach...
, both consisting of repeating
glucoseGlucose , a monosaccharide also known as - grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate...
monomerA monomer is a small molecule that may become chemically bonded to other monomers to form a polymer...
s.
- Cellulose is made by plant
Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
s and is an important structural component of their cell wallA cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to act as a...
s. HumanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s can neither manufacture nor digest it.
- Glycogen, on the other hand, is an animal
Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously...
carbohydrate; humans and other animals use it as a form of energy storage.
Use of carbohydrates as an energy source
- See also carbohydrate metabolism
Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms....
Glucose is the major energy source in most life forms. For instance, polysaccharides are broken down into their monomers (
glycogen phosphorylaseGlycogen phosphorylase is one of the phosphorylase enzymes . Glycogen phosphorylase catalyzes the rate-limiting step in the degradation of glycogen in animals by releasing glucose-1-phosphate from the terminal alpha-1,4-glycosidic bond.- Isozymes :...
removes glucose residues from glycogen). Disaccharides like lactose or
sucroseSucrose, commonly called table sugar, is a moosaccharide of glucose and fructose with the molecular formula C12H22O11. This white, odorless, crystalline powder has a pleasing, sweet taste. It is best known for its role in human nutrition...
are cleaved into their two component monosaccharides.
Glycolysis (anaerobic)
Glucose is mainly metabolized by a very important ten-step pathway called
glycolysisGlycolysis is the metabolic pathway that converts glucose, C
6H
12O
6, into pyruvate, C
3H
6O
3-...
, the net result of which is to break down one molecule of glucose into two molecules of pyruvate; this also produces a net two molecules of
ATPAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, the energy currency of cells, along with two reducing equivalents in the form of converting
NAD+Nicotinamide adenine dinucleotide, abbreviated NAD
+, is a coenzyme found in all living cells. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups, with one nucleotide containing an adenine base and the other containing...
to NADH. This does not require oxygen; if no oxygen is available (or the cell cannot use oxygen), the NAD is restored by converting the pyruvate to
lactate (lactic acid)Lactic acid , also known as milk acid, is a chemical compound that plays a role in several biochemical processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of C
3H
6O
3...
(e. g. in humans) or to
ethanolEthanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug, best known as the type of alcohol found in alcoholic beverages and in modern thermometers. Ethanol is one of the oldest recreational drugs...
plus carbon dioxide (e. g. in
yeastYeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with about 1,500 species currently described; they dominate fungal diversity in the oceans. Most reproduce asexually by budding, although a few do so by binary fission...
). Other monosaccharides like galactose and fructose can be converted into intermediates of the glycolytic pathway.
Aerobic
In aerobic cells with sufficient oxygen, like most human cells, the pyruvate is further metabolized. It is irreversibly converted to
acetyl-CoAAcetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. In chemical structure, acetyl-CoA is the thioester between coenzyme A and acetic...
, giving off one carbon atom as the waste product
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
, generating another reducing equivalent as NADH. The two molecules acetyl-CoA (from one molecule of glucose) then enter the
citric acid cycleThe citric acid cycle — also known as the tricarboxylic acid cycle , the Krebs cycle, or more rarely, the Szent-Györgyi-Krebs cycle — is a series of enzyme-catalysed chemical reactions, which is of central importance in all living cells that use oxygen as part of cellular respiration...
, producing two more molecules of ATP, six more NADH molecules and two reduced (ubi)quinones (via FADH
2 as enzyme-bound cofactor), and releasing the remaining carbon atoms as carbon dioxide. The produced NADH and quinol molecules then feed into the enzyme complexes of the respiratory chain, an electron transport system transferring the electrons ultimately to
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
and conserving the released energy in the form of a proton gradient over a membrane (inner mitochondrial membrane in eukaryotes). Thereby, oxygen is reduced to water and the original electron acceptors NAD
+ and quinone are regenerated. This is why humans breathe in oxygen and breathe out carbon dioxide. The energy released from transferring the electrons from high-energy states in NADH and quinol is conserved first as proton gradient and converted to ATP via ATP synthase. This generates an additional
28 molecules of ATP (24 from the 8 NADH + 4 from the 2 quinols), totaling to 32 molecules of ATP conserved per degraded glucose (two from glycolysis + two from the citrate cycle). It is clear that using oxygen to completely oxidize glucose provides an organism with far more energy than any oxygen-independent metabolic feature, and this is thought to be the reason why complex life appeared only after Earth's atmosphere accumulated large amounts of oxygen.
Gluconeogenesis
In
vertebrateVertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony...
s, vigorously contracting
skeletal muscleSkeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system. It is one of three major muscle types, the others being cardiac and smooth muscle. As its name suggests, skeletal muscle is linked to bone by bundles of collagen fibers known as...
s (during weightlifting or sprinting, for example) do not receive enough oxygen to meet the energy demand, and so they shift to
anaerobic metabolismFermentation is the process of deriving energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. This is in contrast to cellular respiration, where electrons are donated to an exogenous electron acceptor,...
, converting glucose to lactate. The
liverThe liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
regenerates the glucose, using a process called
gluconeogenesisGluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....
. This process is not quite the opposite of glycolysis, and actually requires three times the amount of energy gained from glycolysis (six molecules of ATP are used, compared to the two gained in glycolysis). Analogous to the above reactions, the glucose produced can then undergo glycolysis in tissues that need energy, be stored as glycogen (or starch in plants), or be converted to other monosaccharides or joined into di- or oligosaccharides. The combined pathways of glycolysis during exercise, lactate's crossing via the bloodstream to the liver, subsequent gluconeogenesis and release of glucose into the bloodstream is called the
Cori cycleThe Cori cycle, named after its discoverers, Carl Cori and Gerty Cori, refers to the metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is converted back to lactate.-The...
.
Proteins
Like carbohydrates, some proteins perform largely structural roles. For instance, movements of the proteins
actinActin is a globular, roughly 42-kDa protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
and
myosinMyosins are a large family of motor proteins found in eukaryotic tissues. They are responsible for actin-based motility.Following the discovery by Pollard and Korn of enzymes with myosin-like function in Acanthamoeba castellanii, a large number of divergent myosin genes have been discovered...
ultimately are responsible for the contraction of skeletal muscle. One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be
extremely selective in what they bind.
AntibodiesAntibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses...
are an example of proteins that attach to one specific type of molecule. In fact, the enzyme-linked immunosorbent assay (ELISA), which uses antibodies, is currently one of the most sensitive tests modern medicine uses to detect various biomolecules. Probably the most important proteins, however, are the
enzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at...
s. These molecules recognize specific reactant molecules called
substrateIn biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...
s; they then catalyze the reaction between them. By lowering the
activation energyIn chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined as the energy that must be overcome in order for a chemical reaction to occur. Arrhenius' research was a follow up of the theories of reaction rate by Serbian physicist Nebojsa...
, the enzyme speeds up that reaction by a rate of 10
11 or more: a reaction that would normally take over 3,000 years to complete spontaneously might take less than a second with an enzyme. The enzyme itself is not used up in the process, and is free to catalyze the same reaction with a new set of substrates. Using various modifiers, the activity of the enzyme can be regulated, enabling control of the biochemistry of the cell as a whole.
In essence, proteins are chains of
amino acidAmino acids are molecules containing an amine group, a carboxylic acid group and one of the twenty R-groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H
2NCHRCOOH, where R is an organic substituent...
s. An amino acid consists of a carbon atom bound to four groups. One is an amino group, —NH
2, and one is a
carboxylic acidCarboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -COH, usually written -COOH or -CO2H. Carboxylic acids are Brønsted-Lowry acids — they are proton donors. Salts and anions of carboxylic acids are called...
group, —COOH (although these exist as —NH
3+ and —COO
− under physiologic conditions). The third is a simple
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H
2...
atom. The fourth is commonly denoted "—R" and is different for each amino acid. There are twenty standard amino acids. Some of these have functions by themselves or in a modified form; for instance, glutamate functions as an important
neurotransmitterNeurotransmitters are endogenous chemicals which relay, amplify, and modulate signals between a neuron and another cell. Neurotransmitters are packaged into synaptic vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they...
.
Amino acids can be joined together via a
peptide bondA peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water . This is a dehydration synthesis reaction, and usually occursbetween amino acids...
. In this dehydration synthesis, a water molecule is removed and the peptide bond connects the nitrogen of one amino acid's amino group to the carbon of the other's carboxylic acid group. The resulting molecule is called a
dipeptideA dipeptide is a molecule consisting of two amino acids joined by a single peptide bond.Dipeptides are produced from polypeptides by the action of the hydrolase enzyme dipeptidyl peptidase. Dietary proteins are digested to dipeptides and amino acids, and the dipeptides are absorbed more rapidly...
, and short stretches of amino acids (usually, fewer than around thirty) are called
peptidePeptides are short polymers formed from the linking, in a defined order, of α-amino acids. The link between one amino acid residue and the next is called an amide bond or a peptide bond....
s or polypeptides. Longer stretches merit the title
proteins. As an example, the important blood
serumBlood plasma is the yellow liquid component of blood, in which the blood cells in whole blood would normally be suspended. It makes up about 55% of the total blood volume. It is mostly water and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide...
protein
albuminHuman serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin comprises about half of the blood serum protein. It is soluble and monomeric....
contains 585 amino acid residues.
The structure of proteins is traditionally described in a hierarchy of four levels. The
primary structureIn biochemistry, the primary structure of a biological molecule is the exact specification of its atomic composition and the chemical bonds connecting those atoms...
of a protein simply consists of its linear sequence of amino acids; for instance, "alanine-glycine-tryptophan-serine-glutamate-asparagine-glycine-lysine-…".
Secondary structureIn biochemistry and structural biology, secondary structure is the general three-dimensional form of local segments of biopolymers such as proteins and nucleic acids...
is concerned with local morphology. Some combinations of amino acids will tend to curl up in a coil called an
α-helixA common motif in the secondary structure of proteins, the alpha helix is a right- or left-handed coiled conformation, resembling a spring, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
or into a sheet called a
β-sheetThe β sheet is the second form of regular secondary structure in proteins consisting of beta strands connected laterally by five or more hydrogen bonds, forming a generally twisted, pleated sheet...
; some α-helixes can be seen in the hemoglobin schematic above.
Tertiary structureIn biochemistry and chemistry, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...
is the entire three-dimensional shape of the protein. This shape is determined by the sequence of amino acids. In fact, a single change can change the entire structure. The alpha chain of hemoglobin contains 146 amino acid residues; substitution of the glutamate residue at position 6 with a
valineValine is an α-amino acid with the chemical formula HO
2CCHCH
2.
L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...
residue changes the behavior of hemoglobin so much that it results in
sickle-cell diseaseSickle-cell disease, or sickle-cell anaemia , is a life-long blood disorder characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various complications. The sickling occurs because of a mutation in the...
. Finally
quaternary structureIn biochemistry, quaternary structure is the arrangement of multiple folded protein molecules in a multi-subunit complex.-Description and examples:...
is concerned with the structure of a protein with multiple peptide subunits, like hemoglobin with its four subunits. Not all proteins have more than one subunit.
Ingested proteins are usually broken up into single amino acids or dipeptides in the
small intestineIn vertebrates, the small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where the vast majority of digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large...
, and then absorbed. They can then be joined together to make new proteins. Intermediate products of glycolysis, the citric acid cycle, and the
pentose phosphate pathwayThe pentose phosphate pathway is a process that generates NADPH and pentoses sugars. There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars...
can be used to make all twenty amino acids, and most bacteria and plants possess all the necessary enzymes to synthesize them. Humans and other mammals, however, can only synthesize half of them. They cannot synthesize
isoleucineIsoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested...
,
leucineLeucine is an α-amino acid with the chemical formula HO
2CCHCH
2CH
2. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic...
,
lysineLysine is an α-amino acid with the chemical formula HO
2CCH
4NH
2. This amino acid is an essential amino acid, which means that humans cannot synthesize it. Its codons are AAA and AAG.Lysine is a base, as are arginine and histidine...
,
methionineMethionine is an α-amino acid with the chemical formula HO
2CCHCH
2CH
2SCH
3. This essential amino acid is classified as nonpolar.-Function:...
,
phenylalaninePhenylalanine is an α-amino acid with the formula HO
2CCHCH
2C
6H
5. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. The codons for
L-phenylalanine are UUU and UUC...
,
threonineThreonine is an α-amino acid with the chemical formula HO
2CCHCHCH
3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar...
,
tryptophanTryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
, and
valineValine is an α-amino acid with the chemical formula HO
2CCHCH
2.
L-Valine is one of 20 proteinogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar...
. These are the
essential amino acidAn essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs...
s, since it is essential to ingest them. Mammals do possess the enzymes to synthesize
alanineAlanine is an α-amino acid with the chemical formula CH3CHCOOH. The L-isomer is one of the 20 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid...
,
asparagineAsparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...
, aspartate,
cysteineCysteine is an α-amino acid with the chemical formula HO
2CCHCH
2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is nonpolar and thus cysteine is usually classified as...
, glutamate,
glutamineGlutamine is one of the 20 amino acids encoded by the standard genetic code. Its side chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. It can therefore be considered the amide of glutamic acid. Its codons are CAA and CAG. Glutamine is...
,
glycineGlycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....
,
prolineProline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that humans can synthesize it...
,
serineSerine is an organic compound with the formula HO
2CCHCH
2OH.-Occurrence:...
, and
tyrosineTyrosine or 4-hydroxyphenylalanine, is one of the 20 amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group...
, the nonessential amino acids. While they can synthesize
arginineArginine is an α-amino acid. The
L-form is one of the 20 most common natural amino acids. Its codons are CGU, CGC, CGA, CGG, AGA, and AGG. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health...
and
histidineHistidine is one of the 20 standard amino acids present in proteins. Nutritionally, histidine is considered an essential amino acid in human infants. After reaching several years of age, humans begin to synthesize it and it thus becomes a non-essential amino acid...
, they cannot produce it in sufficient amounts for young, growing animals, and so these are often considered essential amino acids.
If the amino group is removed from an amino acid, it leaves behind a carbon skeleton called an α-
keto acidKeto acids are organic acids containing a ketone functional group and a carboxylic acid group.Common types of keto acids include:*Alpha-keto acid, or 2-oxo acids, such as pyruvic acid have the keto group adjacent to the carboxylic acid...
. Enzymes called
transaminaseIn biochemistry, a transaminase or an aminotransferase is an enzyme that catalyzes a type of reaction between an amino acid and an α-keto acid. Specifically, this reaction involves removing the amino group from the amino acid, leaving behind an α-keto acid, and transferring it to...
s can easily transfer the amino group from one amino acid (making it an α-keto acid) to another α-keto acid (making it an amino acid). This is important in the biosynthesis of amino acids, as for many of the pathways, intermediates from other biochemical pathways are converted to the α-keto acid skeleton, and then an amino group is added, often via
transaminationThere are two chemical reactions known as transamination . The first is the reaction between an amino acid and an alpha-keto acid...
. The amino acids may then be linked together to make a protein.
A similar process is used to break down proteins. It is first hydrolyzed into its component amino acids. Free
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula NH
3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers...
(NH
3), existing as the
ammoniumThe ammonium cation is a positively charged polyatomic cation of the chemical formula NH. It has a formula weight of 18.05 and is formed by the protonation of ammonia...
ion (NH
4+) in blood, is toxic to life forms. A suitable method for excreting it must therefore exist. Different strategies have evolved in different animals, depending on the animals' needs. Unicellular organisms, of course, simply release the ammonia into the environment. Similarly,
bony fishOsteichthyes , also called bony fish, are a taxonomic group of fish that includes the ray-finned fish and lobe-finned fish . The split between these two classes occurred about 450 million years ago....
can release the ammonia into the water where it is quickly diluted. In general, mammals convert the ammonia into urea, via the
urea cycleThe urea cycle is a cycle of biochemical reactions occurring in many animals that produces urea
2CO from ammonia . This cycle was the first metabolic cycle discovered...
.
Lipids
The term lipid comprises a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or nonpolar compounds of biological origin, including
waxWax refers to beeswax or another substance with similar properties. The traditional meaning, beeswax, refers to a substance secreted by bees and used by them in constructing their honeycombs...
es,
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail , which is either saturated or unsaturated...
s, fatty-acid derived
phospholipidPhospholipids are a class of lipids and are a major component of all cell membranes as they can form lipid bilayers. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from...
s,
sphingolipidSphingolipids are a class of lipids derived from the aliphatic amino alcohol sphingosine. These compounds play important roles in signal transmission and cell recognition...
s,
glycolipidGlycolipids are carbohydrate-attached lipids. Their role is to provide energy and also serve as markers for cellular recognition.They occur where a carbohydrate chain is associated with phospholipids on the exoplasmic surface of the cell membrane. The carbohydrates are found on the outer surface...
s and
terpenoidThe terpenoids , sometimes called isoprenoids, are a large and diverse class of naturally-occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in...
s (eg.
retinoidThe retinoids are a class of chemical compounds that are related chemically to vitamin A. Retinoids are used in medicine, primarily due to the way they regulate epithelial cell growth....
s and
steroidA steroid is a terpenoid lipid characterized by its sterane core and additional functional groups. The core is a carbon structure of four fused rings: three cyclohexane rings and one cyclopentane ring. The steroids vary by the functional groups attached to these rings and the oxidation state of the...
s). Some lipids are linear aliphatic molecules, while others have ring structures. Some are aromatic, while others are not. Some are flexible, while others are rigid.
Most lipids have some polar character in addition to being largely nonpolar. Generally, the bulk of their structure is nonpolar or hydrophobic ("water-fearing"), meaning that it does not interact well with polar solvents like water. Another part of their structure is polar or hydrophilic ("water-loving") and will tend to associate with polar solvents like water. This makes them amphiphilic molecules (having both hydrophobic and hydrophilic portions). In the case of
cholesterolCholesterol is a lipidic, waxy steroid found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes, where it is required to establish proper membrane permeability and fluidity...
, the polar group is a mere -OH (
hydroxylIn chemistry, hydroxyl is composed of molecules consisting of an oxygen atom and a hydrogen atom connected by a covalent bond . The neutral form is a hydroxyl radical. The hydroxyl anion is called hydroxide; it is a diatomic ion with a charge of negative one...
or alcohol). In the case of phospholipids, the polar groups are considerably larger and more polar, as described below.
Lipids are an integral part of our daily diet. Most
oilAn oil is any substance that is liquid at ambient temperatures and is hydrophobic but soluble in organic solvents. Oils have a high carbon and hydrogen content and are nonpolar substances. The general definition above includes compound classes with otherwise unrelated chemical structures,...
s and milk products that we use for cooking and eating like
butterButter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications such as baking, sauce making, and frying...
,
cheeseCheese is a food consisting of proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. It is produced by coagulation of the milk protein casein. Typically, the milk is acidified and addition of the enzyme rennet causes coagulation. The solids are separated and pressed into...
,
gheeGhee is a class of clarified butter that originated in South Asia, and is commonly used in South Asian and Middle Eastern cuisine .-Preparation:Ghee is made by simmering unsalted...
etc, are comprised of
fatFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
s. Vegetable oils are rich in various
polyunsaturated fatty acidPolyunsaturated fatty acids are those that contain more than one double bond.- Methylene-Interrupted Polyenes :These fatty acids have 2 or more cis double bonds that are separated from each other by a single methylene group...
s (PUFA). Lipid-containing foods undergo digestion within the body and are broken into fatty acids and
glycerolGlycerol is an organic compound, also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. ...
, which are the final degradation products of fats and lipids.
Nucleic acids
A nucleic acid is a complex, high-molecular-weight biochemical
macromoleculeA macromolecule is a very large molecule most often created by some form of polymerization. In the context of biochemistry, the term may be applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...
composed of nucleotide chains that convey genetic information. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (
RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
). Nucleic acids are found in all living cells and viruses. Aside from the genetic material of the cell, nucleic acids often play a role as second messengers, as well as forming the base molecule for
adenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleotide that plays an important role in cell biology as a coenzyme, that is, the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, the primary energy-carrier molecule found in all living organisms.
Nucleic acid, so called because of its prevalence in cellular
nucleiIn cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as...
, is the generic name of the family of
biopolymerBiopolymers are polymers produced by living organisms. Cellulose and starch, proteins and peptides, and DNA and RNA are all examples of biopolymers, in which the monomeric units, respectively, are sugars, amino acids, and nucleotides....
s. The monomers are called
nucleotideNucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides play central roles in metabolism...
s, and each consists of three components: a nitrogenous heterocyclic
baseIn chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. Bases are also the oxides or hydroxides of metals. A soluble base is also often referred to as an alkali if hydroxide ions are involved. This refers to the Brønsted-Lowry theory of acids and bases...
(either a
purineA purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
or a
pyrimidinePyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...
), a
pentoseA pentose is a monosaccharide with five carbon atoms.They either have an aldehyde functional group in position 1 , or a ketone functional group in position 2 ....
sugarSugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many...
, and a
phosphateA phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
group. Different nucleic acid types differ in the specific sugar found in their chain (e.g. DNA or deoxyribonucleic acid contains 2-
deoxyriboseDeoxyribose, also known as
D-Deoxyribose and 2-deoxyribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group in its linear structure...
s). Also, the nitrogenous bases possible in the two nucleic acids are different:
adenineAdenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
,
cytosineCytosine is one of the four main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
, and
guanineGuanine is one of the five main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, thymine, and uracil. In DNA, guanine is paired with cytosine. With the formula C
5H
5N
5O, guanine is a derivative of purine, consisting of a fused...
occur in both RNA and DNA, while
thymineThymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine always pairs with adenine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be...
occurs only in DNA and
uracilUracil is a common and naturally occurring pyrimidine derivative. Originally discovered in 1900, it was isolated by hydrolysis of yeast nuclein that was found in bovine thymus and spleen, herring sperm, and wheat germ...
occurs in RNA.
Relationship to other "molecular-scale" biological sciences
Researchers in biochemistry use specific techniques native to biochemistry, but increasingly combine these with techniques and ideas from
geneticsGenetics, , a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding...
,
molecular biologyMolecular biology is the study of biology at a molecular level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
and
biophysicsBiophysics is an interdisciplinary science that employs and develops theories and methods of the physical sciences for the investigation of biological systems . Studies included under the branches of biophysics span all levels of biological organization, from the molecular scale to whole organisms...
. There has never been a hard-line between these disciplines in terms of content and technique, but members of each discipline have in the past been very territorial; today the terms
molecular biology and
biochemistry are nearly interchangeable. The following figure is a schematic that depicts one possible view of the relationship between the fields:
- Biochemistry is the study of the chemical substances and vital processes occurring in living organism
In biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
s. BiochemistBiochemists are scientists who are trained in biochemistry. Typical biochemists study chemical processes and chemical transformations in living organisms. The prefix of "bio" in "biochemist" can be understood as a fusion of "biological chemist."-Role:...
s focus heavily on the role, function, and structure of biomolecules. The study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry.
- Genetics is the study of the effect of genetic differences on organisms. Often this can be inferred by the absence of a normal component (e.g. one gene
A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
). The study of "mutantA mutant is an individual, organism, or new genetic character arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not found in the wild type. The natural...
s" – organisms which lack one or more functional components with respect to the so-called "wild typeWild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...
" or normal phenotypeA phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions...
. Genetic interactions (epistasisEpistasis is the interaction between genes. Epistasis takes place when the effects of one gene are modified by one or several other genes, which are sometimes called modifier genes. The gene whose phenotype is expressed is said to be epistatic, while the phenotype altered or suppressed is said to...
) can often confound simple interpretations of such "knock-out" studies.
- Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. The central dogma of molecular biology
The central dogma of molecular biology was first enunciated by Francis Crick in 1958 and re-stated in a Nature paper published in 1970:In other words, 'once information gets into protein, it can't flow back to nucleic acid.'...
where genetic material is transcribed into RNA and then translated into protein, despite being an oversimplified picture of molecular biology, still provides a good starting point for understanding the field. This picture, however, is undergoing revision in light of emerging novel roles for RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
.
- Chemical Biology seeks to develop new tools based on small molecule
In the fields of pharmacology and biochemistry, a small molecule is a low molecular weight organic compound which is by definition not a polymer...
s that allow minimal perturbation of biological systems while providing detailed information about their function. Further, chemical biology employs biological systems to create non-natural hybrids between biomolecules and synthetic devices (for example emptied viral capsids that can deliver gene therapyGene therapy is the insertion of genes into an individual's cells and tissues to treat a disease, such as a hereditary disease in which a deleterious mutant allele is replaced with a functional one. Although controversial, Gene Therapy can also be used for human genetic enhancement changing one's...
or drug molecules).
External links
- The Virtual Library of Biochemistry and Cell Biology
- Biochemistry, 5th ed. Full text of Berg, Tymoczko, and Stryer, courtesy of NCBI
The National Center for Biotechnology Information is part of the United States National Library of Medicine , a branch of the National Institutes of Health. The NCBI is located in Bethesda, Maryland and was founded in 1988 through legislation sponsored by Senator Claude Pepper...
.
- Biochemistry, 2nd ed. Full text of Garrett and Grisham.
- Biochemistry Animation (Narrated Flash animations.)
- SystemsX.ch - The Swiss Initiative in Systems Biology
- Biochemistry Online Resources – Lists of Biochemistry departments, websites, journals, books and reviews, employment opportunities and events.