Biological Systems MCAT Practice Exam

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Study for the Biological Systems MCAT Exam. Ace your test with flashcards and multiple choice questions, including hints and explanations. Be prepared for your exam!

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In the muscle contraction cycle, which event follows ATP binding to the myosin head?

Power stroke occurs
Myosin head releases actin
Calcium binds to troponin
Actin slides over myosin

The correct answer is: Myosin head releases actin

In the muscle contraction cycle, the event that occurs after ATP binding to the myosin head is that the myosin head releases actin. When ATP binds to the myosin head, it causes a conformational change that reduces the affinity of the myosin head for the actin filament. This dissociation is crucial as it allows the cycle to continue; without the release of actin, the muscle contraction could not proceed to the next steps. Subsequently, ATP is hydrolyzed to ADP and inorganic phosphate, which then leads to the re-cocking of the myosin head and its preparation for a new binding with actin. This sequence is vital for the overall process of muscle contraction, where the coordinated interactions between myosin and actin filaments are essential for muscle movement. Understanding this step is key as it highlights the role of ATP not just as an energy source, but also as a necessary component for the proper functioning of the myosin-actin interaction during muscle contraction.