Contractile Proteins

Introduction:

• In a muscle fibre, there are two types of myofilaments present that are responsible for muscle contraction-
  (a) Thin filaments
  (b) Thick filaments

Explanation

a) Thin filament or Actin filaments

• It contains two polymeric filamentous (‘F’ actin filaments) that are a polymer of globular or G actin monomers helically wound together.
• Lengthwise,2 tropomyosin filaments are coiled around the actin filaments.
• Troponin,a complex protein, is present at regular intervals on the tropomyosin which masks the active binding sites for myosin,at resting state.
• Troponin and tropomyosin are known as regulatory proteins, as they play an important role in muscle contraction by regulating the binding of actin and myosin filaments.
  
  
  
  
   

b. Thick filament or Myosin filaments

• The thick filament is a polymeric protein composed of myosin which consists of monomeric units known as meromyosin.
• Each meromyosin has two important parts
  a) Heavy meromyosin (HMM)- Globular head with a short arm
  b) Light meromyosin (LMM)- Tail
• Cross arm is formed as the HMM component projects outwards at a regular distance and angle from each other from the surface of a polymerized myosin filament.
• Globular head is an active ATPase enzyme. It also provides the binding site for ATP and active sites for actin.
  
  
  
  
   

Frequently Asked Questions: FAQs

Q1 What are the types of myofilaments present in the muscle fibre?
Ans:

• In a muscle fibre, there are two types of myofilaments present that are responsible for muscle contraction-
  a) Thin filaments
  b) Thick filaments

Q2 Name the components of the actin filament.
Ans:

a) Troponin
b) Tropomyosin
c) F-actin

Q3 What are the regulatory proteins responsible for? Name them.
Ans:
Troponin and tropomyosin are known as regulatory proteins, as they play an important role in muscle contraction by regulating the binding of actin and myosin filaments.

Q4 Monomeric unit of myosin / thick filament is __________.
Ans: Meromyosin