Q.10 An example for template independent DNA polymerase is
- (A) DNA Polymerase I
- (B) RNA polymerase
- (C) Terminal deoxynucleotidyl transferase
- (D) DNA polymerase III
Template-independent DNA polymerases add nucleotides without a guiding template strand, unlike replicative enzymes. They’re vital in immunology and cloning. This article solves the MCQ, confirming (C) Terminal deoxynucleotidyl transferase as the example.
Defining Template-Independent Polymerases
These enzymes, like TdT, catalyze random deoxynucleotide addition to 3′-OH ends using dNTPs, creating homopolymeric tails (e.g., poly-A). No base-pairing dictates incorporation—activity relies on primer presence and divalent cations. Key in V(D)J recombination for antibody diversity.
Correct Answer: (C) Terminal deoxynucleotidyl transferase
TdT (Terminal deoxynucleotidyl transferase) exemplifies template-independent synthesis, adding N-nucleotides junctionally in B/T-cell receptors. Used in biotech for tailing DNA fragments or labeling probes.Explanation of All Options
Each option’s template dependency:
-
(A) DNA Polymerase I
Incorrect. Template-dependent; fills gaps in Okazaki fragments (E. coli), with 5′-3′ exo for nick translation. -
(B) RNA polymerase
Incorrect. Template-dependent RNA polymerase synthesizes mRNA from DNA; not a DNA polymerase. -
(C) Terminal deoxynucleotidyl transferase
Correct. Adds dNTPs sans template to 3′-ends; no copying mechanism. -
(D) DNA polymerase III
Incorrect. Replicative holoenzyme; highly processive, template-directed for leading/lagging strands.
Option Template-Dependent? Primary Role Example Application (A) DNA Pol I Yes Gap filling Nick translation (B) RNA pol Yes (DNA→RNA) Transcription Gene expression (C) TdT No Random addition Antibody diversity (D) DNA Pol III Yes Replication Genome duplication Biotech Applications
TdT enables homopolymer tailing for cloning (e.g., oligo-dT priming) and apoptosis detection via tailing. In your bioinformatics workflows, pair with BLAST for sequence validation post-tailing.
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