ATP is the energy currency of the cell as it acts as a donor of high energy phosphate. It also acts as a chemical link between catabolism and anabolism. In its active form ATP is complexed with Mg²⁺ or Mn²⁺.

The primary structure is described by the order in which bases occur in a polypeptide. The convention is to arrange them from left to right from 5’ end to 3’ end. 5’ end of the polypeptide is attached to phosphate while 3’ end is usually a free hydroxyl group.

Polynucleotide runs on the backbone of the phosphate-sugar chain. The base pairing of these nucleotide gives secondary structure. The secondary structure of DNA is its double helix which held together by hydrogen bonding between the bases.

According to chargaff’s rules, C=G= 20%; A=T
(A+G) + (T+C) =100%
(A+20) + (T+20) =100%
(A+20) + (A+20) = 100%
2A= 100-40%
A = 30%.