Question

In a DNA molecule, the phosphate group is attached to carbon ______of the sugar residue of its own nucleotide and carbon ______ of the sugar residue of the next nucleotide by ______ bonds.

• A. 5', 3', phosphodiester
• B. 3', 5', phosphodiester
• C. 5', 3', glycosidic
• D. 3', 5', glycosidic

Answer 1

The correct option is A 5', 3', phosphodiester

A phosphodiester bond is a covalent bond in which a phosphate group joins adjacent carbons through ester linkages. The bond is the result of a condensation reaction between a hydroxyl group of two sugar groups and a phosphate group. The diester bond between phosphoric acid and two sugar molecules in the DNA and RNA backbone links two nucleotides together to form oligonucleotide polymers. The phosphodiester bond links a 3' carbon to a 5' carbon in DNA and RNA. During the reaction of two of the hydroxyl groups in phosphoric acid with a hydroxyl group in two other molecules, two ester bonds in a phosphodiester group are formed. the 3’ end has a free hydroxyl group at the 3’ carbon of a sugar, and the 5' end has a free hydroxyl group or phosphate group at the 5’-carbon of a sugar. The synthesis proceeds from the 5’ to the 3’ end.

So the correct option is "5', 3', phosphodiester".