Question

If a DNA molecule has 2000 BP, then calculate the number of N-glycosidic linkages.
(a) 2000
(b) 4000
(c) 8000
(d) 1000

Answer 1

Hint: If a DNA molecule has 2000 BP it means that it has 4000 bases in it as each base pair BP will have 2 nitrogenous bases in it joined by hydrogen bonds. These nitrogen bases are further joined to the C of sugars through N-glycosidic bonds.

Complete Answer:
A glycosidic bond is defined as the bond between sugar and another compound with the elimination of water. N-glycosidic refers to the other compound is a nitrogen-containing compound such as a nitrogenous base. This bond is formed by the reaction of 9’N of the base with 1’C of the sugar. The number of N-glycosidic bonds will be equal to the number of nitrogenous bases present in the DNA strand. Thus, 2000 BP will contain 4000 nitrogenous bases which mean there will be 4000 N-glycosidic bonds.

Additional information: Let us look at the structure of nucleic acids in detail.
Nucleic acids such as Deoxyribonucleic acid (DNA) or Ribonucleic acid (RNA) are long-chain polymers of the monomer nucleotide.

These nucleotides are made up of three components i.e.
(i) Nitrogenous bases such as adenine, guanine, cytosine, thymine, and uracil.
(ii) Sugar which may be deoxyribose or ribose sugar
(iii) Phosphate group Nitrogenous bases are joined to the 1’C of sugars with the help of N-glycosidic bonds to form nucleosides.
These nucleosides are further joined to the phosphate group by using the OH group at 5’C to form a phospho-ester bond. This results in the formation of a nucleotide.
Two nucleotides are linked by a 3’-5’ phosphodiester bond to form a dinucleotide which then gives rise to a polynucleotide.
So, the correct option is ‘4000’.

Note:
- DNA does not have a -OH group at 2’C hence the name deoxyribonucleic acid.
- DNA is made up of a sugar-phosphate backbone with bases projecting outwards.
- The nitrogenous bases such as Adenine (A) and Thymine are joined by 2 hydrogen bonds whereas Cytosine (C) and Guanine (G) are joined by 3 hydrogen bonds.