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Salient Features of Double-Helix Structure of DNA MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET

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Salient Features of Double-Helix Structure of DNA is considered one of the most asked concept.
18 Questions around this concept.

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The hemagglutinin protein in influenza virus contains a long alpha helix, with 53 residues. Which of the following correctly describes the attributes of this alpha helix?

The length is 75.6 A, 14 turns, total of 102 Hydrogen bonds

The length is 106 A, 14 turns, total of 106 Hydrogen bonds

The length is 75.6 A, 14 turns, total of 104 Hydrogen bonds

The length is 75.6 A, 10 turns, total of 102 Hydrogen bonds

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Which one of the following statements on nucleic acids is not true?

The conformation of ribose in DNA is alpha-2’-deoxy-D-ribofuranose.

Hydrolysis of RNA takes place under alkaline conditions unlike DNA, as the 2'-hydroxyl in RNA acts as a nucleophile in an intramolecular displacement.

DNA can occur in different three-dimensional forms.

In DNA, deamination of cytosine to uracil can occur in a non-enzymatic manner.

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Concepts Covered - 1

Salient Features of Double-Helix Structure of DNA

It is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside.
The two chains have antiparallel polarity. It means if one the chain has a polarity of 5'-3', the other has 3'-5'.
The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs (bp).
Adenine forms two hydrogen bonds with Thymine from the opposite strand and vice-versa.
Similarly, Guanine is bonded with Cytosine with three H-bonds.
As a result, always a purine comes opposite to a pyrimidine.
This generates approximately uniform distance between the two strands of the helix.
The two chains are coiled in a right-handed fashion.
The pitch of the helix is 3.4 nm (a nanometre is one-billionth of a metre, that is 10-9 m) and there is roughly 10 bp in each turn.
The distance between a bp in a helix is approximately equal to 0.34 nm.
The plane of one base pair stacks over the other in the double helix. This, in addition to H-bonds, confers stability of the helical structure.