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Small molecule
 
 
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In pharmacology
Pharmacology

Pharmacology is the study of drug action. More specifically it is the study of the interactions that occur between a living organism and exogenous chemicals that alter normal biochemical function....
, a small molecule is a small organic compound
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
 that is biologically active (biomolecule
Biomolecule

A biomolecule is any organic chemistry 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....
) but is not a polymer
Polymer

A 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....
. This term is very loosely used and it may or may not include monomers or primary metabolites, in fact it is generally used to denote molecules that are not protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 which play a endogenous or exogenous biological role, such as cell signalling, are used as a tool in molecular biology
Molecular biology

Molecular biology is the study of biology at a molecule level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry....
 or are a drug
Drug

A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function....
 in medicine
Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
.

These compounds can be natural (such as secondary metabolites) or artificial (such as antiviral drug
Antiviral drug

Antiviral drugs are a class of medication used specifically for treating virus infections. Like antibiotics for bacteria, specific antivirals are used for specific viruses....
s); they may have a beneficial effect against a disease (such as FDA approved drugs) or may be detrimental (such as teratogens and carcinogen
Carcinogen

The term carcinogen refers to any substance, radionuclide or radiation that is an agent directly involved in the promotion of cancer or in the increase of its propagation....
s).

drugs are small molecules, although some drugs can be proteins, e.g.






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In pharmacology
Pharmacology

Pharmacology is the study of drug action. More specifically it is the study of the interactions that occur between a living organism and exogenous chemicals that alter normal biochemical function....
, a small molecule is a small organic compound
Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
 that is biologically active (biomolecule
Biomolecule

A biomolecule is any organic chemistry 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....
) but is not a polymer
Polymer

A 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....
. This term is very loosely used and it may or may not include monomers or primary metabolites, in fact it is generally used to denote molecules that are not protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
 which play a endogenous or exogenous biological role, such as cell signalling, are used as a tool in molecular biology
Molecular biology

Molecular biology is the study of biology at a molecule level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry....
 or are a drug
Drug

A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function....
 in medicine
Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
.

These compounds can be natural (such as secondary metabolites) or artificial (such as antiviral drug
Antiviral drug

Antiviral drugs are a class of medication used specifically for treating virus infections. Like antibiotics for bacteria, specific antivirals are used for specific viruses....
s); they may have a beneficial effect against a disease (such as FDA approved drugs) or may be detrimental (such as teratogens and carcinogen
Carcinogen

The term carcinogen refers to any substance, radionuclide or radiation that is an agent directly involved in the promotion of cancer or in the increase of its propagation....
s).

Drugs

Most drugs are small molecules, although some drugs can be proteins, e.g. insulin
Insulin

Insulin is a hormone with extensive effects on both metabolism and several other body systems . Insulin causes most of the body's cells to take up glucose from the blood , storing it as glycogen in the liver and muscle, and stops use of fat as an energy source....
. Many proteins are degraded if administered orally and most often cannot cross the cell membrane
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
. This is often not the case for small molecules, some though of which are orally available as a Prodrug
Prodrug

A prodrug is a Pharmacology substance that is administered in an inactive form. Once administered, the prodrug is drug metabolism in vivo into an active metabolite....
. Many dietary supplement
Dietary supplement

A dietary supplement, also known as food supplement or nutritional supplement, is a preparation intended to provide nutrients, such as vitamins, Dietary minerals, fatty acids or amino acids, that are missing or are not consumed in sufficient quantity in a person's diet ....
s are small molecules (but not herb extracts, such as ginkgo
Ginkgo

Ginkgo , frequently misspelled as "Gingko", and also known as the Maidenhair Tree after Adiantum, is a unique species of tree with no close living relatives....
).

Secondary metabolites

For organisms to produce small molecules they need one or more specialized enzymes (to create and destroy), which as a result are not that abundant in vertebrates (recent and small + slow population size), but very common in soil bacteria (such as streptomyces
Streptomyces

Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described....
) and fungi, which in particular secrete antibiotics.

Plants also have several secondary metabolite
Secondary metabolite

Secondary metabolites are organic compounds that are not directly involved in the normal cell growth, Biological development or reproduction of organisms....
s, which play a role in cell signalling, pigmentation or in defence, several of which have also been used as drugs (medical and recreational).

  • Alkaloids
  • Glycosides
  • Lipids
  • Flavonoids
  • Nonribosomal peptide
    Nonribosomal peptide

    Nonribosomal peptides are a class of peptide secondary metabolites, usually produced by microorganisms like bacterium and fungi. Nonribosomal peptides are also found in higher organisms, such as nudibranchs, but are thought to be made by bacteria commensurism these organisms....
    s, such as actinomycin-D
  • Phenazines
  • Phenols
    Phenols

    In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl Functional group attached to an aromatic hydrocarbon group....
  • Polyketide
    Polyketide

    Polyketides are secondary metabolites from bacterium, fungi, plants, and animals. Polyketides are biosynthesis by the polymerization of acetyl and propionyl subunits in a similar process to fatty acid metabolism#Synthesis ....
  • Terpenes, including steroids
  • Tetrapyrroles


Investigative tools

Enzymes and receptors are often activated or inhibited by endogenous protein
Ligand (biochemistry)

In biochemistry, a ligand is a Chemical substance that is able to bind to and form a Complex with a biomolecule to serve a biological purpose....
, but can be also inhibited by endogenous or exogenous small molecule inhibitors
Enzyme inhibitor

Enzyme inhibitors are molecules that bind to enzymes and decrease their enzyme activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolism imbalance, many drugs are enzyme inhibitors....
 or activators
Enzyme inhibitor

Enzyme inhibitors are molecules that bind to enzymes and decrease their enzyme activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolism imbalance, many drugs are enzyme inhibitors....
 with can bind to the active site
Active site

The active site of an enzyme contains the catalysis and binding sites. The structure and chemical properties of the active site allow the recognition and binding of the substrate ....
 or on allosteric site
Allosteric regulation

In biochemistry, allosteric regulation is the regulation of an enzyme or other protein by binding an Effector molecule at the protein's allosteric site ....
.

An example is the teratogen and carcinogen phorbol 12-myristate 13-acetate which is a plant terpene which activates protein kinase C
Protein kinase C

Protein kinase C is a family of protein kinases consisting of ~10 isozymes. They are divided into three subfamilies, based on their second messenger requirements: conventional , novel, and atypical....
 resulting in cancer, making it a very useful investigative tool. There is also interest in creating small molecule artificial transcription factors to regulate gene expression
Gene expression

Gene expression is the process by which inheritable information from a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA....
, examples include wrenchnol (a wrench shaped molecule).

See also

  • Chemical compound microarray
    Chemical Compound Microarray

    A chemical compound microarray is a collection of organic chemical compounds spotted on a solid surface, such as glass and plastic. This microarray format is very similar to DNA microarray, protein microarray and antibody microarray....
  • Chemogenomics
    Chemogenomics

    Chemogenomics can be defined as the study of genomics responses to chemical compounds. The goal is the rapid identification of novel drugs and drug targets embracing multiple early phase drug development technologies ranging from drug target identification and drug target validation, over compound design and chemical synthesis to biological t...
  • Peptidomimetic
    Peptidomimetic

    A peptidomimetic is a small protein-like chain designed to mimic a peptide. They typically arise from modification of an existing peptide in order to alter the molecule's properties....