Nucleotides

Content
Chemistry of the Gene 1.  Nucleic Acids and Their Structure
Nucleic acids as genetic material
Transformation experiments
Experiments with bacteriophage (T2) infection
Experiments with tobacco mosaic virus (TMV)
Structure of nucleic acids 
Bases
Nucleosides
Nucleotides
Polynucleotide
Deoxyribonucleic acid (DNA)
Alternative forms of DNA double helices
Z-DNA, a left handed DNA form
RL model
Supercoils in closed DNA
Ribonucleic acid (RNA)


A nucleotide is derived from a nucleoside by addition of a molecule of phosphoric acid. The phosphate molecule is linked with sugar molecule at carbon no. 5 (Fig. 25.11) or at carbon no. 3. Correspondingly nucleotides will be called 5'p3' OH nucleotide and 3'p5' OH nucleotide. In case of ribose, the phosphate group may be linked even at carbon no. 2 of ribose sugar, because hydroxyl group is available at position no. 2 also. However, in biological systems nucleotides have phosphate cither at 5' position or at 3' position. The four nucleotides found in DNA are (i) deoxycytidylic acid or deoxycytidylate, (ii) deoxythymidylic acid or deoxythymidylate, (iii) dexoyadenylic acid or deoxyadenylate and (iv) deoxyguanylic acid or deoxyguanylate. The structures of these four nucleotides are shown in Figure 25.12. Similarly, the four nucleotides found in RNA are (i) cytidylic acid or cytidylate, (ii) uridylic acid or uridylate, (iii) adenylic acid or adenylate and (iv) guanylic acid or guanylate.

A deoxyribosc sugar molecule linked with phosphate group at 5' position.
Fig. 25.11. A deoxyribosc sugar molecule linked with phosphate group at 5' position.


 
Structures of four different 5'p 3' OH nucleotides found in DNA.
Fig. 25.12. Structures of four different 5'p 3' OH nucleotides found in DNA.