Question

Which of the following bonds in DNA links a 3’ pentose sugar to a 5’ pentose sugar?
A. Hydrogen bond
B. Phosphodiester bond
C. Glycosidic bond
D. None of the above

Answer 1

The DNA backbone is a polymer with an alternating sugar-phosphate sequence. These bonds are central to all life on Earth as they make up the backbone of the strands of nucleic acid. Deoxyribose sugars are joined in the 3'-hydroxyl and 5'-hydroxyl groups to the phosphate groups in ester compounds.

Complete answer:
In DNA the phosphodiester bond is the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another, deoxyribose in DNA. It also forms strong covalent bonds between 5-carbon ring carbohydrates over ester bonds the phosphate group. The phosphate groups in the phosphodiester bond are negatively charged because they are negatively charged at pH 7.
These repulsion forces cause phosphates to take opposite sides of the DNA strands and are neutralized by histones proteins, metal ions such as polyamines, and magnesium. The phosphodiester bond to be formed and the nucleotides to be joined, the tri-phosphate or di-phosphate forms of nucleotide building blocks are broken apart to give off the energy needed to drive the enzyme-catalyzed reaction. A single phosphate or two phosphates are known as pyrophosphates that break away and catalyze the reaction due to which phosphodiester bond is formed.
So, the correct option is (B)-‘Phosphodiester bond’.

Note: Hydrolysis of phosphodiester bonds can be catalyzed due to the action of phosphodiesterase which plays an important role in repairing DNA sequences. A crucial step in the cloning of genes is to recombine the chosen gene into a plasmid vector. The use of two separate endonucleases, which cleave on either side of the gene producing distinctive single-strand ends, enables the separation of the gene from a restriction fragment.