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Question #46862
The Question
During an in vitro experiment, an isolated skeletal muscle fiber is subjected to a severe drop in physiological pH (acidosis). Under a polarized light microscope, the distinct striation pattern collapses, characterized by the 'fuzzing' and disappearance of the H-zone and I-bands. This structural loss occurs entirely independent of calcium influx or ATP hydrolysis. What is the primary molecular mechanism responsible for this specific structural collapse?
Options
- A.
The low pH induces spontaneous release of Ca²⁺ from the sarcoplasmic reticulum, leading to maximal overlap of actin and myosin filaments.
- B.
The acidic pH alters the zwitterionic state of constituent amino acids, disrupting the electrostatic interactions that maintain the tertiary structure of myofilaments.
- C.
Acidosis denatures the troponin complex, permanently unmasking the myosin-binding sites on F-actin and causing irreversible cross-bridge cycling.
- D.
The pH shift directly hydrolyzes the phosphodiester bonds within the heavy meromyosin (HMM) component, detaching the globular heads.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Skeletal Muscle Striation Pattern|Amino Acid Zwitterion Equilibrium|Actin|Myosin|pH homeostasis
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating the 'Biomolecules' concept of pH-dependent zwitterion equilibrium with the 'Locomotion and Movement' concept of sarcomere architecture.
Common Misconception: Students memorize that the H-zone and I-band disappear during maximal muscle contraction (Sliding Filament Theory).
Therefore, they will reflexively jump to Option A (calcium release/overlap), failing to read the constraint that this collapse is independent of ATP/Ca²⁺ and is instead a biochemical denaturation event.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Structural Organisation in Animals - Class 11 |
| Concept | Skeletal Muscle Striation Pattern |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |