Ribose is a
pentose (five-carbon sugar) that is a component of the ribonucleic acid (RNA),
where it alternates with phosphate groups to form the 'back-bone' of the RNA
polymer and binds to nitrogenous bases. Ribose phosphates are components of the
nucleotide coenzymes and are utilized by microorganisms in the synthesis of the
amino acid histidine. Its close relative, deoxyribose, is a constituent of
deoxyribonucleic acid (DNA), where it alternates with phosphate groups to form
the 'back-bone' of the DNA polymer and binds to nitrogenous bases. The presence
of deoxyribose instead of ribose is one difference between DNA and RNA. Ribose
has one more oxygen atom in its molecule than deoxyribose. Ribose has a five
member ring composed of four carbon atoms and one oxygen. Hydroxyl groups are
attached to three of the carbons. The other carbon and a hydroxyl group are
attached to one of the carbon atoms adjacent to the oxygen. In deoxyribose, the
carbon furthest from the attached carbon is stripped of the oxygen atom in what
would be a hydroxyl group in ribose. The sugar (ribose or deoxyribose) molecules
in the nucleic acid are all oriented in the same direction. Their carbon atoms
are numbered: the 5' carbon atom is always on the side of the sugar molecule
that faces the leading end, while the 3' carbon atom always faces the tail end.
Nucleotide is the structural unit of a nucleic acid. A nucleotide consists of
either a nitrogenous heterocyclic base (purine or pyrimidine) , a pentose sugar
(ribose or deoxyribose) and a phosphate group attached at the 5' position on the
sugar. A nucleoside consists of only a pentose sugar linked to a purine or
pyrimidine base, without a phosphate group. Purine bases are Adenine, Guanine
and Hypoxanthine (examples of purine nucleosides are Adenosine,
2'-Deoxyadenosine, Guanosine, 2'-Deoxyguanosine, Inosine, 2'-Deoxyinosine).
Pyrimidine bases are Cytosine, Thymine, and Uracil (examples of pyrimidine
nucleosides are Cytidine, 2'-Deoxyguanosine, 5-Methyluridine,
2'-Deoxy-5-Methyluridine, Uridine, 2'-Deoxyuridine). The nucleoside derivatives
are involved in important functions in cellular metabolism and are used to
synthesize enzyme inhibitors, antiviral agents, and anticancer
agents.
Cytosine is a
pyrimidine base, occurring condensed with ribose or deoxyribose to form the
nucleosides cytidine and deoxycytidine in animal cells. It is a fundamental unit
or base of nucleic acids. When N9 is linked to the C1 of ribose, cytosine forms
a pyrimidine nucleoside called cytidines which are phosphorylated with from one
to three phosphoric acid groups to form the three nucleotides; cytidine
monophosphate (CMP), cytidine diphosphate (CDP), and cytidine triphosphate (TTP)
respectively. When N1 is linked to the C1 of deoxy ribose, deoxy nucleosides
and nucleotides are formed from cytosine and deoxyribose; deoxycytidine
monophosphate (dCMP), deoxycytidine diphosphate (dCDP), deoxycytidine
triphosphate (dCTP). CTP is the source of the cytidine in RNA (ribonucleic acid)
and deoxycytidine triphosphate (dCTP) is the source of the deoxycytidine in DNA
(deoxyribonucleic acid). CTP is involved in the formation of adenosine
triphosphate (ATP) as a donator of phosphate groups to adenosine diphosphate
(ADP).
- Cytidine
Monophosphate (CMP, Cytidylic Acid;
):
a nucleotide, the 5'-phosphate of cytidine, acting as a carrier of
N-acetylneuraminic acid in glycoprotein synthesis.
- Cytidine
Diphosphate (CDP): a nucleotide, the 5'-pyrophosphate of cytidine, acting as a
carrier of choline and ethanolamine in the phospholipid synthesis.
- Cytidine
Triphosphate (CTP): a nucleotide, the 5'-triphosphate of cytidine; precursor in
the synthesis of ribonucleic acid and of CDP- and CMP-linked
compounds.
- Deoxycytidine Monophosphate (dCMP): a nucleotide,
the 5'-phosphate of deoxycytidine (deoxy-, also called desoxy, is a prefix for
the designation of compounds which contain one less atom of oxygen than the
reference substance).
- Deoxycytidine Diphosphate (dCDP): a nucleotide, the
5'-pyrophosphate of deoxycytidine.
- Deoxycytidine Triphosphate (dCTP): a nucleotide, the
5'-triphosphate of deoxycytidine; an precursor in the synthesis of
DNA.
Chemically
modified nucleotides substituted or attached by special chemical groups or
elements are studied and used to inactivate the normal biological operation in
the living organism and the function of important enzymes. |