Nucleic acids such as DNA and RNA are polymers of monomeric nucleotides. Each nucleotide is made up of phosphoric acid, sugar (5-carbon), and nitrogenous base (or nucleobase). There are five nitrogenous bases that serve as fundamental units of the genetic code: (1) adenine, (2) guanine, (3) cytosine, (4) thymine, and (5) uracil. These nitrogenous bases may be classified into purines and pyrimidines.
Cytosine, thymine, and uracil are pyrimidine nitrogenous bases. Cytosine can be differed from the other pyrimidines by having a keto group at position 2 and an amine group at position 4 in its heterocyclic aromatic ring. It has a chemical formula of C4H5N3O.
In DNA and RNA, cytosine matches with guanine forming three hydrogen bonds. Cytosine, though, is relatively unstable and can be converted into uracil (via spontaneous deamination). This alteration can be corrected by DNA repair systems such as by the use of the enzyme uracil glycosylase. If not repaired, this may lead to a point mutation.
Cytidine and deoxycytidine are nucleosides of cytosine. When phosphorylated with three phosphoric acid groups, they become cytidine triphosphate (CTP) and deoxycytidine triphosphate (dCTP), which are nucleotides that build up RNA and DNA molecules, respectively.
A cytidine triphosphate is a nucleotide that forms part of DNA or RNA. It may also serve as a co-factor to enzymes. It can transfer its phosphate to convert ADP to ATP.