Question

Is DNA a Polymer?

Answer 1

Hint: Nucleic acid is of two types in all living systems i.e., deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is genetic material in all organisms except some viruses. RNA is genetic material in riboviruses. DNA is a substance that controls the inheritance of traits from one generation to the next.

Complete answer:
DNA is an elongated polymer of deoxyribonucleotides. It is an acidic substance present in the nucleus of a cell, which was first identified by Friedrich Meischer in 1869. He named it "Nuclein". Altmann discovered that these substances are acidic in nature and hence he named the substance as nucleic acid. The length of DNA is typically defined as the number of nucleotides or a pair of nucleotides mentioned as base pairs (bp) present in it. This is also one of the characteristic features of an organism. For example E. coli has 4.6 x $10^6$ bp and the human genome has 3.3 x 10^9 bp.
The basic unit of DNA has three components- a nitrogenous base, a pentose sugar and a phosphate group. The two types of nitrogenous bases are:
(i) Purines: Heterocyclic, 9-membered double ring structure with N at position 1,3,7,9. E.g., Adenine and Guanine.
(ii) Pyrimidines: Heterocyclic, 6- membered single ring structure with N at 1 and 3 position. E.g., Cytosine and Thymine are present in DNA and Uracil is present at the place of thymine in RNA.
A polynucleotide chain shows the following type of linkage in its component:
(i) N-glycosidic linkage- A nitrogenous base is linked to the pentose sugar with the help of an N-glycosidic linkage to form a nucleoside.
(ii) Phosphoester linkage: When a phosphate group is linked to 5'-OH of a nucleoside with the help of phosphodiester linkage, a nucleotide is formed. Both of the nucleotides are linked through 3'-5' phosphodiester linkage to make a dinucleotide.
A polymer thus formed has a free phosphate moiety at the 5'-end of sugar, which is referred to as the 5'-end of the polynucleotide chain. The backbone during a polynucleotide chain is made thanks to sugar and phosphates. The nitrogenous base projects from the backbone.

Note:
Two lines of investigations helped in the derivation of DNA structure i.e., X-ray Crystallography and Chargaff’s rule. X-ray crystallography was done by Maurice Wilkins and Rosalind Franklin to obtain very fine X-ray diffraction pictures of DNA. Chargaff’s rule is not applicable to single-stranded DNA.