The sequence of nucleotides in the nucleic acid is called the primary structure of
DNA. It is written from the 5’ to 3’ direction, where the 5’-end is on the left end,
and the one-letter abbreviation of the nitrogen base represents the nucleotides. It
is the sequence of nucleotides that carries the genetic information. Nucleotides
are in two types: purine (Adenine and Guanine) and pyrimidine (Cytosine and
Thymine). Adenine (A) pairs with thymine (T) with two hydrogen bonds,
Guanine (G) pairs with Cytosine (C) with three hydrogen bonds.

Molecular Biology is not the study of the molecules of living organisms.
Biochemistry, also called Biological Chemistry, fits this definition because it
studies biological molecules and their chemical reactions in cells (metabolism).
The adjective “Molecular” before Biology does not refer to all molecules of living
organisms but only to the two crucial ones: nucleic acids and proteins (structural
and catalytic, as well as motors, membrane transporters and regulators).
Molecular Biology is not the classical study of genes. This corresponds to