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  • Choose the incorrect statementOption: 1 Each  actin is a po

Choose the incorrect statement

Option: 1

Each 'F' actin is a polymer of monomeric 'G' (Globular) actins.


Option: 2

An actin filament is made of two 'F' (filamentous) actins helically wound to each other.


Option: 3

In the resting state a subunit of troponin masks the active binding sites for acting  on the myosin filaments.


Option: 4

Myosin filaments are called thick filaments


Answers (1)

best_answer

 

 

Structure of Contractile Proteins -

Actin Filament:

  • Each actin (thin) filament is made of two ‘F’ (filamentous) actins helically wound to each other. 
  • Each ‘F’ actin is a polymer of monomeric ‘G’ (Globular) actins. 
  • Two filaments of another protein, tropomyosin also run close to the ‘F’ actins throughout its length. 
  • A complex protein Troponin is distributed at regular intervals on the tropomyosin (which bears actin-binding sites)
  • In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.

Myosin Filament:

  • Each myosin (thick) filament is also a polymerised protein. 
  • Many monomeric proteins called Meromyosins constitute one thick filament.
  • Each meromyosin has two important parts, a globular head with a short arm and a tail, the former being called the heavy meromyosin (HMM) and the latter, the light meromyosin (LMM). 
  • The HMM component, i.e.; the head and short arm projects outwards at a regular distance and angle from each other from the surface of a polymerised myosin filament and is known as a cross arm. 
  • The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for actin.

In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments. Hence the correct option is c. 

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Gaurav

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