Everything about Nucleobase totally explained
Nucleobases (or Nucleotide bases) are the parts of
RNA and
DNA that may be involved in pairing (see also
base pairs). These include
cytosine,
guanine,
adenine,
thymine (
DNA) and
uracil (
RNA). These are abbreviated as C, G, A, T, and U, respectively. They are usually simply called
bases in
genetics. 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, respectively.
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
purines (abbreviated as R). Cytosine, thymine, and uracil are all
pyrimidines (abbreviated as Y).
The system of a base
covalently bound to the 1'
carbon of a
ribose or
deoxyribose is called a
nucleoside, and a nucleoside with one or more
phosphate groups attached at the 5' carbon is called a
nucleotide.
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 only modified base is 5-methylcytidine (m5C). In RNA, there are many modified bases, including pseudouridine (Ψ), dihydrouridine (D), inosine (I), ribothymidine (rT) and 7-methylguanosine (m7G).
Hypoxanthine and
xanthine are two of the many bases created through
mutagen presence, both of them through deamination (replacement of the amine-group with a hydroxyl-group). Hypoxanthine is produced from
adenine, xanthine from
guanine. Similarly, deamination of
cytosine results in
uracil.
Structure
- The "skeleton" of adenine and guanin is purine, hence the name purine-bases.
- The "skeleton" of cytosine, uracil and thymine is pyrimidine, 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 nucleobases analogues exist.
The most common application are used as fluorescent probes, either directly or indirectly, such as
Aminoallyl nucleotide 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 and
isocytosine or the fluorescent 2-amino-6-(2-thienyl)purine and pyrrole-2-carbaldehyde.
In medicine, several
nucleoside analogues 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're adminisered as nuclosides as charged nucleotides can't easily cross cell membranes.
Further Information
Get more info on 'Nucleobase'.
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