Joints and muscle movement — A/L Biology

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1 question with a worked solution

1. According to the sliding filament model of skeletal muscle contraction, what direct event causes the myosin head to detach from the active binding site on actin?
   1. A) Binding of a new ATP molecule to the myosin head
   2. B) Hydrolysis of bound ATP into ADP and inorganic phosphate
   3. C) Release of calcium ions from the sarcoplasmic reticulum
   4. D) Phosphorylation of troponin by creatine kinase
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   Correct answer: A) Binding of a new ATP molecule to the myosin head

   Following the power stroke, a new molecule of ATP binds to the nucleotide-binding site on the myosin head. This causes an allosteric conformational change that drastically reduces myosin's affinity for actin, causing the cross-bridge to detach. Without ATP, detachment cannot occur (rigor mortis).

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   Step 1: Cross-bridge cycle steps: - Cocking: ATP hydrolysis energizes myosin head. - Attachment: Ca²⁺ exposes binding site; myosin attaches to actin. - Power stroke: ADP + Pi release causes power stroke. - Detachment: Binding of fresh ATP detaches myosin from actin. Answer: Binding of a new ATP molecule to the myosin head.
   Modelled on: the A/L Biology examination pattern

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Where does Joints and muscle movement fit in the syllabus?

Year 2 · Term 1