Question

Which of the following is true about phosphodiester linkage?

• A. 3’-phosphate group of one nucleotide unit is joined to the 5’-hydroxyl group of the next nucleotide
• B. 3’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide
• C. 5’-phosphate group of one nucleotide unit is joined to the 3’-hydroxyl group of the next nucleotide
• D. 5’-phosphate group of one nucleotide unit is joined to the 5’-hydroxyl group of the next nucleotide

Hint:

Phosphodiester bonds form the stable, repeating sugar-phosphate backbone of nucleic acids, essential for the structure and function of DNA and RNA.

Answer 1

The Correct Option is C

Phosphodiester linkages form the backbone of nucleic acids (DNA and RNA). In this linkage: - The 5’-phosphate group of one nucleotide is covalently bonded to the 3’-hydroxyl group of the next nucleotide. - This creates a continuous chain of nucleotides in which the phosphate group connects the sugar molecules of adjacent nucleotides, linking them together in a strand.

(1) Phosphodiester Bond Formation:
- This type of bond forms the backbone of both DNA and RNA molecules and is essential for maintaining the integrity of the genetic code.
- The directionality of the strand is determined by the 5’ and 3’ ends of the nucleotides.

(2) Why Other Options Are Incorrect:
- Option 1: This would create an incorrect bond, as the phosphate group is joined to a hydroxyl group on the 5’ carbon, which does not form a valid phosphodiester linkage.
- Option 2: This option describes an incorrect bonding between two phosphate groups, which doesn't occur in natural nucleic acid structures.
- Option 4: This would imply two phosphate groups are linked incorrectly and is not how phosphodiester bonds are formed.

Conclusion: The correct phosphodiester linkage in nucleic acids is between the 5’-phosphate group of one nucleotide and the 3’-hydroxyl group of the next nucleotide, forming the backbone of the nucleic acid strand.