The roles of actin, myosin, calcium ions and ATP in myofibril contraction
Muscle fibres contract when two proteins, actin and myosin, repeatedly grab and pull past each other. Calcium ions start the process, and ATP powers each pull.
Formula
ATP → ADP + Pᵢ (hydrolysis powers myosin head movement)
Real World
Usain Bolt's 9.58-second 100 m sprint required billions of actin–myosin cross-bridge cycles firing almost simultaneously across his leg muscles, each one powered by a single ATP molecule.
Exam Focus
State the sequence precisely: calcium release → binding-site exposure → cross-bridge formation → power stroke → ATP-driven detachment → re-cocking.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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