Question

In a segment of DNA 3.2 kilobases are present. If the DNA segment has 820 adenine molecules, then what will be the number of cytosines?
(a)1560
(b)1480
(c)780
(d)740

Answer 1

A base pair is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. .DNA pairing always occurs between adenine and thymine and also between guanine and cytosine. The number of Adenines is equal to Thymines and that of cytosine is equal to guanine. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA and RNA.

Complete answer:
The pairing in DNA occurs as Adenine-Thymine and Cytosine-Guanine. So, the number of adenine equals thymine while the cytosines equal to guanine. There are 3.2 kilobases (3,200 kb), and it has 820 adenines and so are the number of thymines. So, 1640 bases are Adenines and Thymines. So, the remaining bases are 3200-1640 = 1560. So, 1560 includes Cytosines and Guanines. So, the number of cytosines are (1560/2 = 780). In complementary base pairing, the companion bases are always specific. Thus pairing occurs always between adenine and thymine and also between guanine and cytosine. A-T pairing occurs through two Hydrogen bonds and G-C pairing occurs through three Hydrogen bonds. On account of the specificity in base pairing, the base sequence in one strand will be exactly complementary to that in another. This makes the two strands complementary to each other.

Additional Information: -DNA is an information tape in which the hereditary messages are encoded in the form of a base-pair sequence.
-It constitutes the essential substance of genes and the apparatus by which genes act.
-DNA is primarily concerned with the storage, transmission, and expression of vast genetic information.
So, the correct answer is' 780’.

Note: -The nitrogenous bases of nucleic acids are heterocyclic, nitrogen-containing organic compounds.
-They are of two kinds, purines, and pyrimidines. The commonest purines of DNA and RNA are adenine and guanine.
-The commonest pyrimidines of DNA include cytosine and thymine and those of RNA include cytosine and uracil.