Question

With which of the following molecules does $C{a}^{2+}$ released from the sarcoplasmic reticulum bind?

• A. Myosin
• B. Actin
• C. Troponin
• D. Tropomyosin

Answer 1

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.