Question

The pyrimidine bases present in DNA are
A. Cytosine and adenine
B. Cytosine and guanine
C. Cytosine and thymine
D. Cytosine and uracil

Answer 1

Hint: Pyrimidine is a six-membered nitrogen heterocyclic compound with molecular formula C4H4N2. Its bases are weakly basic. Pyrimidines are stabilized by the resonance among atoms in the ring that gives most of the bonds a partial double bond character.

Complete answer:
-Pyrimidines are aromatic nitrogen heterocycles with its structure similar to the benzene but containing two nitrogen atoms at 1 and 3 positions of the ring. Along with the purines pyrimidines serve as the informational monomers of RNA. Pyrimidines are planar molecules and they are characterized by the strong UV absorption generally near 260 nm.
-Depending on the pH, pyrimidine bases may exist in different tautomeric defined forms. Pyrimidines are hydrophobic at neutral pH, and therefore relatively insoluble. Substituted pyrimidines are broadly distributed in nature and are the components of coenzymes, deoxyribonucleic acids (DNA), ribonucleic acids (RNA).
-The three pyrimidine nitrogenous bases uracil (U), cytosine (C) and thymine (T) are the modified forms of the aromatic compound pyrimidine. Thymine and cytosine are two major pyrimidine bases in base pairs and DNA with adenine and guanine respectively.
-The three pyrimidine nitrogenous bases, along with two purine bases, act as genetic material in all the living organisms. Their function is two-fold: to pass information to offspring from parents through replication, meiosis, mitosis and between various organisms through the horizontal gene transfer; and to encode the genes and regulatory information.

Hence, the correct answer is option (C).

Note: Pyrimidine derivatives also play an important role in development of drugs, either in concert with the other compounds or on their own. They have been used in a wide variety of pharmaceuticals including anti-epilepsy medication, general anesthetics, drugs for treating high blood pressure, anti-malaria medication, and HIV medication.