Q.59 How many GTP molecules are required for the translocation of tRNA from P
site to E site during translation elongation process in bacteria?
One GTP molecule is required for the translocation of tRNA from the P site to the E site during bacterial translation elongation. This process relies on elongation factor G (EF-G) hydrolyzing GTP to drive the movement. The answer aligns with standard mechanisms in prokaryotic protein synthesis for CSIR NET Life Sciences preparation.
Introduction
In bacterial translation elongation, tRNA translocation from P site to E site is a critical step powered by GTP hydrolysis. This query—”How many GTP molecules are required for the translocation of tRNA from P site to E site during translation elongation process in bacteria?”—is common in CSIR NET Life Sciences exams. Understanding the role of EF-G and GTP ensures accurate peptide chain extension.
Translation Elongation Overview
Translation elongation in bacteria involves three main steps: aminoacyl-tRNA binding (EF-Tu, 1 GTP), peptide bond formation (ribozyme-catalyzed, no GTP), and translocation (EF-G, 1 GTP). After peptide bond formation, the ribosome holds peptidyl-tRNA in the A site and deacylated tRNA in the P site. Translocation shifts peptidyl-tRNA to the P site and deacylated tRNA to the E site, advancing mRNA by one codon.
Translocation Mechanism
EF-G binds the pre-translocation ribosome in its GTP-bound form, stabilizing a rotated hybrid state (A/P and P/E positions). GTP hydrolysis by EF-G unlocks the ribosome, biases forward tRNA-mRNA movement via a power stroke and Brownian ratchet, and allows EF-G·GDP release. The deacylated tRNA fully moves from P to E site during this single GTP-dependent event; no additional GTP is needed for E site occupancy or exit.
GTP Requirement Details
Exactly one GTP molecule is hydrolyzed per translocation cycle by EF-G. Studies confirm GTP hydrolysis accelerates translocation and ensures EF-G dissociation, but binding alone promotes movement—hydrolysis mainly prevents reversal. Total GTP per elongation cycle: 2 (EF-Tu + EF-G).
MCQ Options Analysis
Assuming standard CSIR NET-style options (1, 2, 0, or more):
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1 GTP: Correct. Matches EF-G catalysis for P-to-E tRNA shift.
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2 GTP: Incorrect. Confuses with full elongation cycle (EF-Tu + EF-G); translocation uses only EF-G.
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0 GTP: Wrong. Spontaneous translocation is slow; GTP hydrolysis is essential for efficiency.
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More than 1: Incorrect. No evidence for extra GTP in bacterial P-to-E movement.
This distinction is key for exams, as eukaryotic eEF2 uses one GTP similarly.
