Multiple Choice
Which of the following types of cell signaling involves a cell releasing a signal molecule that binds to receptors on its own surface, thereby affecting itself?
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10. Cell Signaling
Introduction to Cell Signaling
Multiple Choice
Which of the following best describes the role of calcium ions (\(\mathrm{Ca^{2+}}\)) in the sliding filament model of muscle contraction?
A
They inhibit the interaction between actin and myosin by blocking the binding sites.
B
They provide the energy required for the myosin head to detach from actin.
C
They directly hydrolyze ATP to power the sliding of filaments.
D
They bind to troponin, causing a conformational change that exposes myosin-binding sites on actin.
Verified step by step guidance1
Understand the sliding filament model of muscle contraction: This model explains how muscles contract by the interaction of actin and myosin filaments. Myosin heads bind to actin filaments, forming cross-bridges, and then pull the actin filaments inward, shortening the muscle fiber.
Recognize the role of calcium ions (\(\mathrm{Ca^{2+}}\)): Calcium ions are crucial in regulating the interaction between actin and myosin. They do not directly provide energy or hydrolyze ATP but instead play a regulatory role.
Identify the role of troponin and tropomyosin: In a relaxed muscle, tropomyosin blocks the myosin-binding sites on actin. Troponin is a protein complex associated with tropomyosin and actin.
Explain how calcium ions interact with troponin: When calcium ions (\(\mathrm{Ca^{2+}}\)) are released from the sarcoplasmic reticulum during muscle contraction, they bind to troponin. This binding causes a conformational change in the troponin-tropomyosin complex.
Describe the result of calcium binding: The conformational change in troponin moves tropomyosin away from the myosin-binding sites on actin, exposing these sites. This allows myosin heads to bind to actin, initiating the cross-bridge cycle and muscle contraction.
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