Q.103 From the point of view of the enzymatic reactions, which of the following DOES NOT belong here?
(A) Telomerase
(B) Reverse transcriptase
(C) Taq polymerase
(D) Primase
Taq polymerase does not belong with the other enzymes, as it is a standard DNA-dependent DNA polymerase used in PCR, while the others are all RNA-dependent DNA polymerases (reverse transcriptases) or RNA polymerase.
Correct Answer
(C) Taq polymerase [ from prior context on replication enzymes]
Option Analysis
(A) Telomerase
Reverse transcriptase. Uses internal RNA template (TERC) to synthesize DNA repeats (TTAGGG) onto chromosome 3′ ends, solving end-replication problem in eukaryotes.
(B) Reverse transcriptase
Classic RNA-dependent DNA polymerase from retroviruses (e.g., HIV). Copies viral RNA genome into DNA for provirus integration using viral RNA as template.
(C) Taq polymerase
Does NOT belong. DNA-dependent DNA polymerase from Thermus aquaticus bacterium. Extends DNA primers on DNA templates during PCR; thermostable for high-temp cycling, but cannot use RNA templates.[web: prior PCR context]
(D) Primase
RNA polymerase (DNA-dependent). Synthesizes short RNA primers (10-12 nt) on single-stranded DNA templates to initiate DNA replication; later removed by RNase H/DNA pol I.
| Enzyme | Template | Product | Biological Role |
|---|---|---|---|
| Telomerase | RNA (TERC) | DNA | Telomere extension |
| Reverse transcriptase | RNA (viral) | DNA | Retroviral replication |
| Taq polymerase | DNA | DNA | PCR amplification |
| Primase | DNA | RNA | Primer synthesis |
Enzymatic Mechanism Grouping
A, B, D share replication initiation/elongation roles involving RNA templates or products:
-
Telomerase/RT: RNA → DNA (reverse transcription)
-
Primase: DNA → RNA (priming)
Taq is purely DNA → DNA, lab-evolved for biotech (PCR), not natural replication.
In molecular biology enzymatic reactions, identifying grouping patterns is key for exams. Taq polymerase stands apart from telomerase, reverse transcriptase, and primase because it’s DNA-dependent DNA polymerase for PCR, while others handle RNA templates/products in replication.
Core Distinction: Template Dependency
-
Reverse transcriptases (telomerase, RT): RNA → DNA
-
Primase: DNA → RNA primers
-
Taq: DNA → DNA (thermostable PCR tool)
Why Taq Doesn’t Fit Natural Replication
Taq thrives at 95°C for denaturation but lacks reverse transcription or RNA priming capability, making it lab-specific unlike the others’ cellular roles.
Biotech students: Master this distinction for CSIR-NET, GATE biotech questions on replication enzymology.
