Nucleoside = base + (deoxy)riboseNucleotide = base + (deoxy)ribose + phosphate; linked by 3'-5' phosphodiester bond.

5' end of incoming nucleotide bears the triphosphate (energy source for the bond).Triphosphate bond is target of 3' hydroxyl attack.

Purines: A, GPyrimidines: C, T, U

Deamination of cytosine forms uracil.Methylation of uracil makes thymine.Deamination of 5-methylcytosine forms thymine.

Deamination of adenine forms hypoxanthine.Deamination of guanine forms xanthine.

Amino acids necessary for purine synthesis: glycine, aspartate, glutamine.Pyrimidine out of carbamoyl phosphate, aspartate.