Here is some important nomenclature for the MCAT. Nucleosides are glycosides of ribose or deoxyrobose with replacement of the anomeric hydroxyl group by a purine or pyrimidine. (The anomeric hydroxyl group is the hydroxyl group remaining from the carbonyl in a sugar's straight chain form after hemi-acetal formation). Nucleotides are phosphate esters of nucleosides.

DNA and RNA are polymers of nucleotides. DNA holds the genetic code, and the several forms of RNA (mRNA, tRNA, and rRNA) together enable the translation of the genetic code into the sequence of proteins.

The phosphate group(s) of a nucleotide are acidic. The two protons of the phosphate group of AMP are governed by pK+'s of 3.8 and 6.2, respectively, so at neutral pH, the dianion of AMP predominates. The negatively charged phosphate groups present in DNA and RNA give the molecules an overall negative charge which enables electrophoretic separation in the laboratory.