With which of the following molecules does Ca2+ released from the sarcoplasmic reticulum bind?
A
Myosin
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B
Actin
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C
Troponin
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D
Tropomyosin
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Solution
The correct option is C Troponin The thin filaments in muscle fibres are made of F-actin (filamentous actin), tropomyosin, and troponin proteins. F-actin and tropomyosin are long molecules wound around each other. Troponin is a much smaller protein molecule and is located at regular intervals on the thin filament. When an action potential arrives, calcium ions are released from the sarcoplasmic reticulum into the sarcoplasm. They bind with the troponin molecules, causing the strands of tropomyosin to shift, thereby exposing the myosin-binding sites on the thin filaments. Myosin makes up the thick filaments of the muscle fibres.