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Nucleobase
 
 
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Nucleobases (or Nucleotide bases) are the parts of DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
 that may be involved in pairing (see also base pairs). The main ones are cytosine
Cytosine

Cytosine is one of the five main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached ....
, guanine
Guanine

Guanine 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....
, adenine
Adenine

Adenine 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 cofactor s nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and Protein biosynthesis, as a chemical component of DNA and RNA....
 (DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
), thymine
Thymine

Thymine is one of the four bases in the nucleic acid of DNA that make up the letters GCAT. The others are adenine, guanine, and cytosine. Thymine always pairs with adenine....
 (DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
) and uracil
Uracil

Uracil 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....
 (RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
), abbreviated as C, G, A, T, and U, respectively. They are usually simply called bases in genetics
Genetics

Genetics , a discipline of biology, is the science of heredity and Genetic 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....
. Because A, G, C, and T appear in the DNA, these molecules are called DNA-bases; A, G, C, and U are called RNA-bases.

Uracil replaces thymine in RNA.






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Encyclopedia


Nucleobases (or Nucleotide bases) are the parts of DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
 that may be involved in pairing (see also base pairs). The main ones are cytosine
Cytosine

Cytosine is one of the five main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached ....
, guanine
Guanine

Guanine 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....
, adenine
Adenine

Adenine 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 cofactor s nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and Protein biosynthesis, as a chemical component of DNA and RNA....
 (DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
), thymine
Thymine

Thymine is one of the four bases in the nucleic acid of DNA that make up the letters GCAT. The others are adenine, guanine, and cytosine. Thymine always pairs with adenine....
 (DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
) and uracil
Uracil

Uracil 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....
 (RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
), abbreviated as C, G, A, T, and U, respectively. They are usually simply called bases in genetics
Genetics

Genetics , a discipline of biology, is the science of heredity and Genetic 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....
. Because A, G, C, and T appear in the DNA, these molecules are called DNA-bases; A, G, C, and U are called RNA-bases.

Uracil replaces thymine in RNA. These two bases are identical except that uracil lacks the 5' methyl group. Adenine and guanine belong to the double-ringed class of molecules called purine
Purine

Purine is a heterocyclic compound 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....
s (abbreviated as R). Cytosine, thymine, and uracil are all pyrimidine
Pyrimidine

Pyrimidine 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....
s (abbreviated as Y).

The system of a base covalently bound to the 1' carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
 of a ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
 or deoxyribose
Deoxyribose

Deoxyribose, 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....
 is called a nucleoside
Nucleoside

Nucleosides are glycosylamines consisting of a nucleobase bound to a ribose or deoxyribose sugar. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine....
, and a nucleoside with one or more phosphate
Phosphate

A phosphate, an inorganic chemical, is a Salt of phosphoric acid. Inorganic phosphates are mining to obtain phosphorus for use in agriculture and industry....
 groups attached at the 5' carbon is called a nucleotide
Nucleotide

Nucleotides are molecules that comprise the structural units of RNA and DNA. Additionally, nucleotides play central roles in metabolism. In that capacity, they serve as sources of chemical energy , participate in cell signaling , and are incorporated into important cofactors of enzymatic reactions ....
.

Apart from adenosine (A), cytidine (C), guanosine (G), thymidine (T) and uridine (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytidine (m5C). In RNA, there are many modified bases, including pseudouridine, dihydrouridine (D), inosine (I), ribothymidine (rT) and 7-methylguanosine (m7G).

Hypoxanthine
Hypoxanthine

Hypoxanthine is a naturally occurring purine derivative. It is occasionally found as a constituent of nucleic acids where it is present in the anticodon of tRNA in the form of its nucleoside inosine....
 and xanthine
Xanthine

Xanthine , , is a purine base found in most body tissues and fluids and in other organisms. A number of mild stimulants are derived from xanthine, including caffeine and theobromine....
 are two of the many bases created through mutagen
Mutagen

In biology, a mutagen is a physical or chemical agent that changes the genetic information of an organism and thus increases the frequency of mutations above the natural background level....
 presence, both of them through deamination (replacement of the amine-group with a carbonyl-group). Hypoxanthine is produced from adenine
Adenine

Adenine 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 cofactor s nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and Protein biosynthesis, as a chemical component of DNA and RNA....
, xanthine from guanine
Guanine

Guanine 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....
. Similarly, deamination of cytosine
Cytosine

Cytosine is one of the five main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached ....
 results in uracil
Uracil

Uracil 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....
.

Structure

  • The "skeleton" of adenine and guanine is purine
    Purine

    Purine is a heterocyclic compound 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....
    , hence the name purine-bases.
  • The "skeleton" of cytosine, uracil and thymine is pyrimidine
    Pyrimidine

    Pyrimidine 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....
    , hence pyrimidine-bases.


Main bases

These are incorporated into the growing chain during RNA and/or DNA synthesis.

Modified purine bases

These are examples of modified adenosine or guanosine.

Modified pyrimidine bases

These are examples of modified cytidine, thymidine or uridine.

Novel Bases

A vast number of nucleobase analogues exist. The most common applications are used as fluorescent probes, either directly or indirectly, such as Aminoallyl nucleotide
Aminoallyl nucleotide

Aminoallyl nucleotides are used in post-labeling of nucleic acid to be used in microarrays. These nucleotides are formally known as 5--nucleotides since the aminoallyl group is usually attached to carbon 5 of the pyrimidine ring of uracil and cytosine....
 which are used to label cRNA or cDNA in microarrays. Several groups are working on alternative "extra" base pairs to extend the genetic code, such as isoguanine
Isoguanine

Isoguanine or 2-hydroxyladenine is a purine base that is an isomer of guanine. It is a product of oxidative damage to DNA and has been shown to cause mutation....
 and isocytosine
Isocytosine

Isocytosine or 2-aminouracil is a pyrimidine base that is an isomer of cytosine. It is used in combination with isoguanine in studies of unnatural nucleic acid analogues of the normal base pairs in DNA....
 or the fluorescent 2-amino-6-(2-thienyl)purine and pyrrole-2-carbaldehyde.

In medicine, several nucleoside analogues
Nucleoside analogues

Nucleoside analogues are a range of antiviral products used to prevent viral replication in infected cells. The most commonly used is Aciclovir....
 are used as anticancer and antiviral agents. The viral polymerase incorporates these compounds with non-canon bases. These compounds are activated in the cells by being converted into nucleotides, they are administered as nuclosides as charged nucleotides cannot easily cross cell membranes.

See also

  • Nucleoside
    Nucleoside

    Nucleosides are glycosylamines consisting of a nucleobase bound to a ribose or deoxyribose sugar. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine....
  • Nucleotide
    Nucleotide

    Nucleotides are molecules that comprise the structural units of RNA and DNA. Additionally, nucleotides play central roles in metabolism. In that capacity, they serve as sources of chemical energy , participate in cell signaling , and are incorporated into important cofactors of enzymatic reactions ....
  • DNA
    DNA

    Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
  • RNA
    RNA

    Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....


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