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Question #45798
The Question
In an experimental setup, a cardiac muscle fiber is treated with a pharmacological agent that completely inhibits its G-protein coupled secondary messenger cascade, effectively preventing the release of calcium ions from the sarcoplasmic reticulum. The intracellular fluid is artificially maintained with high concentrations of ATP. Under these conditions, which of the following accurately describes the physiological state of the myofilaments?
Options
- A.
The myosin heads remain firmly bound to actin, creating a state of rigor because the chemomechanical coupling is disrupted.
- B.
Myosin heads hydrolyze ATP and remain in a high-energy 'cocked' state with ADP and inorganic phosphate bound, but cannot form cross-bridges.
- C.
The absence of calcium directly inhibits the ATPase activity of the heavy meromyosin (HMM), preventing ATP hydrolysis.
- D.
Tropomyosin undergoes a conformational shift to unmask the active sites, but the lack of calcium prevents the execution of the power stroke.
Check Your Answer
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
Myosin_ATPase|cAMP|Calcium_Release
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between the biochemical activation of myosin (which requires ATP hydrolysis) and the structural availability of actin (which requires Calcium-dependent unmasking).
A common misconception is that if muscle contraction fails, ATP hydrolysis itself must be blocked, or students confuse the conditions required for rigor mortis (lack of ATP) with flaccid paralysis (lack of Ca2+).
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 |