Question

The contractile regulatory proteins that mask and unmask active sites in the sarcomere are:

• A. Troponin and tropomyosin
• B. Troponin and myosin
• C. Actin and myosin
• D. Troponin 1 and troponin C

Answer 1

The correct option is A Troponin and tropomyosin

• The contractile regulatory proteins that mask and unmask active sites in the sarcomere are troponin and tropomyosin.
  
• The two tropomyosin filaments run close to the actin filaments throughout its length.
  
• The troponin units are distributed throughout the length of tropomyosin filaments and mask the active binding sites for myosin.
  
• During muscle contraction, the increased calcium ion levels lead to their binding to a subunit of troponin and unmasking the active sites for myosin filaments.
  

So, the correct answer is option A.