Question

Which among these is not a pyrimidine?
A. Guanine
B. Thymine
C. Uracil
D. Cytosine.

Answer 1

Hint: Genetic material consists of two types of macromolecules such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) that found is found in the different organism in a single-stranded or double-stranded form which may be enclosed in the nuclear membrane. DNA is present majorly in a complex organism.

Complete answer:
DNA or RNA is composed of Phosphate groups with deoxyribose and ribose sugar respectively with two nitrogenous bases pairs that are categories into purine and pyrimidine.
Purines (Adenine as A and Guanine as G) are nine membered double-ring structures with nitrogen at 1, 3, 7, and 9 positions. While in the case of pyrimidine (Cytosine as C, thymine as T, and Uracil as U), bases have a structure which is six-membered rings with nitrogen at 1 and 3 positions. This base-pair are lying opposite to each other in DNA or RNA strands via a hydrogen bond, between T and A two hydrogen bonds are present while in between C and G three hydrogen bonds are present.
The backbone of the DNA duplex is built up by alternate deoxyribose sugar and phosphate groups inside the duplex; both purine and pyrimidine are attached with hydrogen bonding and hold both strands together. In the case of RNA, the molecule backbone is made up of ribose sugar with phosphate group along with purine and pyrimidine base pair but Uracil is present instead of Thymine base pair.
Hence, the correct option is A.

Note: DNA is of several kinds on the basis of its structure or orientation of DNA duplex. Such as A-DNA which is right-handed that possesses 11 base pair per turn, B-DNA which is called balanced DNA right-handed spiral, C-DNA which has 9 base pair per turn while D-DNA has 8 bases pair, and Z-DNA is called zig-zag DNA.