Q.7 DNA is synthesized in the cell by
DNA is synthesized in cells by DNA polymerase. This is a fundamental concept in molecular biology, central to DNA replication during cell division.
Option Breakdown
The question tests knowledge of enzymes in DNA synthesis (replication). Here’s each option explained:
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(1) Taq polymerase: A heat-stable DNA polymerase from Thermus aquaticus, used in PCR for amplifying DNA in labs. It does not function in natural cellular DNA synthesis.
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(2) DNA polymerase: Correct. These enzymes (e.g., Pol III in bacteria, Pol δ/ε in eukaryotes) add nucleotides to the 3′-OH end of a growing strand, using the template strand during replication. They synthesize DNA in the 5’→3′ direction.
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(3) Topoisomerase: Relieves supercoiling ahead of the replication fork by nicking DNA strands. It manages DNA topology but does not synthesize DNA.
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(4) RNAase: Degrades RNA (ribonuclease). It has no role in DNA synthesis; RNA is involved via primase, but RNase breaks it down.
Correct Answer: (2) DNA polymerase. Others are involved in replication but not direct synthesis.
Introduction to DNA Synthesized by DNA Polymerase
Understanding DNA synthesized by DNA polymerase is crucial for NEET Biology and GATE Life Sciences aspirants tackling replication questions. This guide solves the exact DNA is synthesized in the cell by MCQ, explaining Taq polymerase, topoisomerase, RNAase roles vs. true DNA synthesis enzyme. Perfect for molecular biology revision.
DNA Polymerase in Replication
DNA polymerase catalyzes phosphodiester bond formation, adding dNTPs (dATP, dGTP, dCTP, dTTP) to the primer’s 3′-OH using the template strand. Key types:
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Bacterial: DNA Pol III (main replicase), Pol I (fills gaps).
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Eukaryotic: Pol α (primed start), δ/ε (bulk synthesis).
It proofreads via 3’→5′ exonuclease activity for accuracy.
Why Not Other Enzymes?
| Enzyme | Role | Why Not DNA Synthesis? |
|---|---|---|
| Taq Polymerase | PCR amplification | Lab tool, not cellular. |
| Topoisomerase | Relieves DNA supercoils | Topology management only. |
| RNAase | RNA degradation | Destroys RNA, irrelevant to DNA. |
Option (2) uniquely builds new DNA strands.
Exam Tips for DNA Replication Questions
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Link to S-phase of cell cycle; replication is semiconservative (Meselson-Stahl).
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Practice: Primase makes RNA primer; ligase seals Okazaki fragments.
