Question

1. Given below is a schematic diagram of a portion of DNA. (4)
(a) How many strands are shown in the diagram?
(b) How many nucleotides have been shown in each strand?
(c) Name the parts numbered 1,2,3,4 and 5 respectively.
(d) Name the DNA unit constituted by the parts 1, 2 and 3 collectively.​

Answer 1

Explanation:

a) Two strands of DNA are shown in the diagram. The two linear strands form the double strands of DNA.

b) Each strand has two nucleotides. The nucleotide is a structure comprising of a nucleoside and a phosphate group linked to it. Nucleoside comprises of a nitrogenous base and a ribose sugar linked together.

c) The part named "1" is a phosphate group, the part named "2" is a ribose sugar. the part named "3" is a pyrimidine, the part named "4" is hydrogen bond which links the pyrimidine and purine. The part named '5" is purine.

d) The part 1 is a phosphate group, the part 2 is a ribose sugar and the part 3 is a nitrogenous base and hence they collectively constitute Nucleotide.