Question

Backbone of DNA is formed by:-
A) Sugar – Phosphate - Sugar
B) Nitrogen base – Phosphate - Sugar
C) Phosphate – Nitrogen base - Sugar
D) Base pairs

Answer 1

Hint:-Deoxyribonucleic acid is a double helix structure composed of two polynucleotide chains that coil around each other to form a genetic molecule carrying genetic instructions for the growth, development and reproduction of organisms. The two strands of DNA chain run in opposite directions to each other and are thus called antiparallel.

Complete Answer:-DNA is a heteropolymer of deoxyribonucleotides, which are made up of a pentose sugar, nitrogenous bases and a phosphate moiety. Each nucleotide is composed of one of the four nitrogen molecules containing nucleobases (cytosine, guanine, adenine or thymine), a deoxyribose sugar and a phosphate group.
Two successive nucleotides are joined by covalent bonds called phosphodiester bonds present between the sugar of one nucleotide and phosphate of the alternating sugar phosphate. Hydrogen bonds are formed between the nitrogen bases. According to the base pairing rule to make double-stranded DNA, adenine forms a base pair with thymine and cytosine forms a base pair with guanine.
The backbone of DNA is the portion which provides structural support to the two strands and is made up of alternating sugar and phosphate groups while nitrogenous bases face inside.
So, Option (B) is the correct answer.

Note:- DNA was first isolated by Friedrich Miescher and its molecular structure was identified by Francis Crick and James Watson. They postulated the Watson and crick model of the DNA double helix which is accepted worldwide. The eukaryotic DNA is organized into genetic structures called chromosomes. Before cell division, these chromosomes are duplicated (by DNA replication) and provide a complete set of chromosomes for each daughter cell, whereas a circular coiled DNA is located in the cytoplasm of a prokaryotic cell.