Q. If a linear DNA molecule has 2000 bps then how many phosphodiester bonds and glycosidic bonds would be presents in it respectively ?
(1) 2000 and 2000
(2) 3998 and 4000
(3) 4000 and 4000
(4) 4000 and 8000
The correct option is (2) 3998 and 4000.
This is a nucleoside composed of a purine or a pyrimidine base and a ribose or deoxyribose sugar. When a phosphate group binds to the OH group present at the carbon at 5th position
(CH2OH) of sugar it is called a Nucleotide.
The bond formed between the sugar and the phosphate group is a phosphoester bond but when this phosphate group forms a bond with another hydroxyl group of a sugar molecule it is called as phosphodiester bond because two ester bonds are involved.
The number of phosphodiester bonds are 2×(n-1)
Where n= number of base pairs in a DNA, and the equation is multiplied by 2, as DNA is double-stranded.
2 x (n-1) = 2 x (2000-1) = 1999 x 2 = 3998.
Number of glycosidic bonds will be double the number of base pairs.