Question

Number of phosphodiester bonds found in one turn of DNA is ________.
A. 18
B. 10
C. 40
D. 38

Answer 1

Hint: Phosphoester bond is a bond which is formed between the sugar and the phosphate group. In DNA, two phosphodiester bonds are present between two adjacent base pairs. The phosphate group makes the DNA negatively charged.

Complete answer: The bond formed between the sugar molecule and the phosphate group is a phosphodiester bond, so when the phosphate group forms a bond with another hydroxyl group of the sugar molecule, it is considered to be a phosphodiester bond since two ester bonds are involved. In a single turn of DNA, there are 10 base pairs and two phosphodiester bonds present between the two adjacent base pairs, so that there must be 9 phosphodiester bonds on one side of the 10-base pair and 9 phosphodiester bonds on the other side. Therefore, the total number of phosphodiester bonds identified at one turn of DNA is 18. When two hydroxyl groups of phosphoric acid react with hydroxyl groups on other molecules, phosphodiester bond occurs to form two ester bonds. The phosphodiester bond is the relation between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another in both DNA and RNA.
Hence, the correct answer is option A.

Note: The phosphodiester bond, that links sugar molecules and phosphate molecules in the backbone, is among the most essential components of DNA and RNA building because it protects the integrity of the genetic code and supports life on this planet.