Nucleotide

A nucleotide is a that consists of 3 portions: a, a , and one or more  s. In the most common nucleotides the base is a derivative of  or , and the sugar is the  (five-carbon sugar)  or. Nucleotides are the of, with three or more bonding together in order to form a nucleic acid.

Nucleotides are the structural units                                  of, , and several cofactors - , , ,  and. In the they have important roles in  and signaling.



Deoxynucleotides
NOTE  If in place of ribose, the sugar deoxyribose is present the prefix `''deoxy ''` may be added before the name of the nucleoside in all cases except thymidine

Synthesis
Salvage synthesis refers to the reuse of parts of in resynthesizing new nucleotides. Salvage synthesis requires both breakdown and synthesis reactions in order to exchange the useful parts.

Purine ribonucleotides
By using a variety of isotopically labeled compounds it was demonstrated that the sources of the atoms in purines are as follows:

The of purine nucleotides by which these precursors are incorporated into the purine ring, proceeds by a 10 step pathway to the branch point intermediate IMP, the nucleotide of the base. AMP and GMP are subsequently synthesized from this intermediate via separate, two step each, pathways. Thus purine are initially formed as part of the ribonucleotides rather than as.

Six enzymes take part in IMP synthesis. Three of them are multifunctional:
 * (reactions 2, 3, and 5)
 * (reactions 6, and 7)
 * (reactions 9, and 10)

Reaction 1. The pathway starts with the formation of. is the enzyme that activates, which is primarily formed by the , to PRPP by reacting it with. The reaction is unusual in that a pyrophosphoryl group is directly transferred from ATP to C1 of R5P and that the product has the α configuration about C1. This reaction is also shared with the pathways for the synthesis of the pyrimidine nucleotides,, and. As a result of being on (a) such (a) major metabolic crossroad and the use of energy, this reaction is highly regulated.

Reaction 2. In the first reaction unique to purine nucleotide biosynthesis, catalyzes the displacement of PRPP's pyrophosphate group (PPi) by Gln's amide nitrogen. The reaction occurs with the inversion of configuration about ribose C1, thereby forming β- (5-PRA) and establishing the anomeric form of the future nucleotide. This reaction which is driven to completion by the subsequent hydrolysis of the released PPi, is the pathway's flux generating step and is therefore regulated too.

Reaction 3.

Protection Chemistry
Nucleic acids can be synthetised in the lab using s, typically this is acchived by protecting a purified nucleoside or nucleobase, a protected base is called a. these can be used to obtain analogues not present in nature and/or to create an.

Nucleotide Frequencies
A connection has been proposed between the Fibonacci numbers and concerning the proportions of s in the.