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Question #45799
The Question
During endurance training, skeletal muscles can undergo phenotypic switching from fast-twitch (white) to slow-twitch (red) fibers. This involves the epigenetic silencing of the fast-twitch Myosin Heavy Chain (MHC-II) gene. Which of the following best explains the molecular mechanism of this repression and its direct consequence on the sliding filament theory?
Options
- A.
Removal of acetyl groups from histone tails increases their positive charge, tightly binding the MHC-II promoter DNA to silence it, which subsequently lowers the rate of ATP hydrolysis during cross-bridge cycling.
- B.
Acetylation of lysine and arginine residues in the histone octamer increases its affinity for negatively charged DNA, silencing the MHC-II gene and reducing the frequency of the power stroke.
- C.
Epigenetic methylation of the MHC-II gene directly alters the allosteric structure of the actin-binding site on the myosin head, converting it to a slow-twitch phenotype.
- D.
Silencing of the MHC-II gene decreases the release of calcium ions from the sarcoplasmic reticulum, which directly slows down the binding of calcium to Troponin subunit C.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Myosin_Heavy_Chain_Gene|Chromatin_Remodeling|Transcription_Factors
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating Molecular Basis of Inheritance (Histone charge and packaging) with Locomotion and Movement (Muscle fiber types and ATPase activity).
Students often confuse the effect of acetylation (which activates transcription by neutralizing histone positive charge) with deacetylation (which represses).
Furthermore, they must connect the silencing of the fast-twitch MHC gene to its physiological outcome: a slower rate of ATP hydrolysis at the myosin cross-bridge.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Locomotion and Movement - Class 11 |
| Concept | Cross-bridge Cycling Energy |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |