LIFE SCIENCE

Detailed explanation-1: -Pyrimidine is a simple aromatic ring composed of two nitrogen atoms and four carbon atoms, with hydrogen atoms attached to each carbon. The carbon and nitrogen atoms are connected via alternating double and single bonds. This bond structure allows for resonance, or aromaticity, causing the ring to be very stable.

Detailed explanation-2: -The primary structure of a purine is two carbon-nitrogen rings. Cytosine, thymine, and uracil are classified as pyrimidines which have a single carbon-nitrogen ring as their primary structure (Figure 1.1. 1). Each of these basic carbon-nitrogen rings has different functional groups attached to it.

Detailed explanation-3: -Single-ring nitrogenous bases are called pyrimidines, while double-ringed structures are called purines.

Detailed explanation-4: -Adenine (A) and Guanine (G) both have a double ring structure and are called purines.

Detailed explanation-5: -The two-carbon nitrogen ring bases (adenine and guanine) are purines, while the one-carbon nitrogen ring bases (thymine and cytosine) are pyrimidines.