Question

Describe the role of specific proteins involved in the muscle contraction process.

Answer 1

The muscle fibres are made up of many fibrils called myofibrils.The myofibrils are divisible into individual filaments made up of contractile proteins-

1. Myosin
2. Actin
3. Tropomyosin
4. Troponin

1)Myosin: It is composed of two large polypeptide heavy chains and four smaller light chains. These polypeptides combine to form a molecule that consists of two globular heads and a long tail.

Function:Each globular head has two important sites:

• Actin binding site ( myosin comes in contact with actin)
• ATPase site (breaks ATP)

2)Actin: These filaments stretch from Z line to the edge of H zone

3)Tropomyosin:It covers the binding site of actin i.e. it prevents interaction between actin and myosin filaments

4)Troponin:It is made up of 3 sub-units-

• Troponin T: It binds the other troponin components to tropomyosin
• Troponin I: It inhibits the ineraction of myosin with actin
• Troponin C:It contains binding site for calcium that initiates the muscle contraction