Question

The DNA strands are antiparallel due to
A. H bonds
B. Phospho - diester bond
C. Disulphide bond
D. Phosphate bonds

Answer 1

Hint:-All the genetic information of an individual cell is present inside the nucleus of a cell. The nucleus contains the genetic material in the form of DNA or sometimes in the form of RNA in some organisms.
Both DNA and RNA are the nucleic acids made up of many nucleotides. Each nucleotide contains a phosphate molecule, a sugar molecule and a nitrogen base.

Complete Answer:-
The sugar molecule in DNA is a pentose sugar molecule having five carbon atoms in its structure. This sugar is deoxyribose in nature. There are a total four types of nitrogen bases in a DNA molecule named as - A, T, G and C.
The complete DNA molecule is made up of two polynucleotide chains. Both these chains are complementary and anti-parallel to each other. In a nucleotide molecule, the sugar component is bounded with nitrogen base with the help of glycosidic bond and it is bounded with phosphate molecule with the help of phosphodiester bond.
Both the strands of a DNA molecule are held together by hydrogen bonds (H bonds). These hydrogen bonds are present between the nitrogen bases of both strands. In a single strand of a DNA molecule, the two consequent sugar molecules are bound with each other with the help of phosphodiester linkage. In both the strands of a DNA molecule, the direction of the phosphodiester bond is opposite. This is the reason why both the strands are antiparallel to each other.

Thus the correct answer is Phospho - diester bond, option B.

Note:- The nitrogen base adenine (A) of a DNA strand binds to thymine (T) of the complementary strand by the two hydrogen bonds. Also, the nitrogen base guanine (G) binds with the cytosine (C) by three hydrogen bonds.In a DNA molecule plane of one base pair stacks over the other in a double helix manner. This in addition to H- bonds confers additional stability to the helical structure of DNA.