Question

How do you calculate the molecular weight of DNA?

Answer 1

Hint: DNA is the nucleic acid made up of nitrogen base, sugar, and a phosphate group. It is not easy to calculate the molecular weight of the whole DNA strand so for its calculation a small part is taken out with the help of restriction enzymes.

Complete answer:
DNA is made up of the number of deoxyribonucleotides which form a long double chain. It is made up of nitrogen bases like adenine, guanine, cytosine, and thymine which present on ribose sugar, and the two sugar bases get connected by the phosphate group through a phosphodiester bond. In humans 23 pairs of chromosomes are present and each genome consists of 23 chromosomes which consist of 3.165× ${10}^9$ base pair. For the calculation of the molecular weight of DNA the long strand of DNA cut out into smaller pieces with the help of a restriction enzyme, then the DNA fragment is placed in gel electrophoresis to determine its length. By its length, base-pair gets calculated. For molecular mass, the number of base pairs gets multiplied by the average molecular mass of one base pair. The average molecular mass of one base pair is 660 g/mol. So the formula comes out as Molecular mass= Number of base-pair × Average molecular mass of one base pair.

Note:
The average molecular mass of one base pair 660 g/mol is taken in the case of double-stranded DNA, if the DNA is single-stranded then the average molecular mass will be taken as 330 g/mol. Inside the living organism, the DNA will remain double-stranded but in lab condition, it will be taken as single-stranded to make the calculation easier.