Which subunit of the troponin regulatory protein complex directly binds calcium ions to initiate cross-bridge formation between actin and myosin?

Answer and explanation

Correct answer: B. Troponin C (TnC)

- Troponin T (): binds to tropomyosin,
- Troponin I (): inhibits the active binding site on actin,
- Troponin C (): contains high-affinity binding sites for ions.
  1. Step 1: The thin myofilament consists of F-actin, tropomyosin, and the heterotrimeric troponin complex.
  2. Step 2: The troponin complex consists of three subunits:
  3. Step 3: When action potentials release from the sarcoplasmic reticulum, binds to , causing a conformational shift that pulls tropomyosin away, unmasking the myosin-binding sites on actin.
Answer
Troponin C (TnC)
Why not the others: 'Troponin T' attaches the troponin complex to the elongated tropomyosin polymer; 'Troponin I' physically blocks the myosin-binding site in the resting state; 'Heavy Meromyosin (HMM)' is a structural component of the thick myosin filament, not the troponin complex.

Practise more Excretory Products, Locomotion and Movement, Neural Control.

Free questions with an explanation for every one, and full timed NEET UG mock tests.

All Excretory Products, Locomotion and Movement, Neural Control questionsTake a mock test

More Excretory Products, Locomotion and Movement, Neural Control questions