Question

Which one or more of the following statements correctly describe(s) the addition of N-nucleotides during the rearrangement of the immunoglobulin heavy chain-encoding gene?

• A. ( Addition of N-nucleotides is template encoded. )
• B. ( N-nucleotides are added by terminal deoxynucleotidyl transferase. )
• C. ( The added N-nucleotides are common in V-D and D-J junction. )
• D. ( N-nucleotides are added by the DNA polymerase II. )

Hint:

When studying immunoglobulin gene rearrangement, remember that the addition of N-nucleotides by TdT enhances junctional diversity, a critical component of the immune system's ability to recognize a wide array of antigens.

Answer 1

The Correct Option is B

Understanding the Addition of N-nucleotides: During the rearrangement of the immunoglobulin heavy chain-encoding gene, the process involves several critical steps to enhance the diversity of antibodies. One of these steps includes the addition of N-nucleotides at the junctions of gene segments. 
Analysis of Options: (A) Template encoded: This statement is incorrect. The addition of N-nucleotides is not template encoded; rather, it occurs in a template-independent manner. 
(B) Terminal deoxynucleotidyl transferase: This is correct. Terminal deoxynucleotidyl transferase (TdT) is an enzyme that adds N-nucleotides in a template-independent fashion during V(D)J recombination, contributing to the diversity of the antibody repertoire. 
(C) Common in V-D and D-J junction: This is also correct. The addition of N-nucleotides by TdT commonly occurs at the junctions between V-D and D-J segments during the recombination process. 
(D) DNA polymerase II: This statement is incorrect. DNA polymerase II is not involved in the addition of N-nucleotides; this process is specifically mediated by TdT.