Tag: structure of muscle

Questions Related to structure of muscle

In a resting muscle fibre, tropomyosin partially covers

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. Ca-binding sites on actin

  2. Ca-binding sites on troponin

  3. Actin binding sites on myosin

  4. Myosin binding sites on actin

Show answer
Correct Option: D
Explanation:
  • The myofibril is composed of two types of filaments. They are thick filament (Myosin) and Thin filament (Actin).
  • 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. In the resting state tropomyosin partially covers myosin binding site on actin.
  • Increase in Ca++ level leads to the binding of calcium with a subunit of troponin i.e troponin-C on actin filaments and thereby remove the masking of active sites for myosin. Utilizing the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge.
  • Hence In a resting muscle fibre, tropomyosin partially covers myosin binding sites on actin.
  • So, the correct answer is 'Myosin binding sites on actin'.

Which one of the following is the thick filament of muscle?

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. Actin

  2. Troponin

  3. Tropomyosin

  4. Myosin

Show answer
Correct Option: D
Explanation:
  • Myofibril is made up of two types of filaments. They are thick filament (myosin) and thin filament (actin). Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively
  • Each myosin (thick) filament is a polymerized protein. Many monomeric proteins called meromyosins constitute one thick filament.
  • Hence myosin is the thick filament of muscle.
  • So, the correct answer is 'Myosin'.

Which one of the following is wrongly matched?

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. Myosin - contractile protein

  2. Tendon - connective tissue

  3. Smooth muscle - involuntary muscle

  4. Troponin - fibrous protein

Show answer
Correct Option: D
Explanation:
A. Myosin are made up of polymerised protein which make thick myofilament. They are found in A- band of sarcomere and are contractile protein.
B. Tendon is dense regular connective tissue which join muscle to bone and made up of white collagen fibres.
C. Smooth muscle is non striated muscle with tapering ends and spindle shaped. They are involuntary muscles which are not under control and do not get fatigue.
D. Thin myofilament is made up of three proteins - actin, tropomyosin and troponin. Actin is a globular protein. Tropomyosin is a fibrous protein. At regular intervals of tropomyosin, a complex protein called troponin. It is a trimeric protein having three units - troponin I, troponin T and troponin C.
So, the correct answer is 'Troponin-fibrous protein'.

The microfilaments of a muscle

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. Are arranged in compartments known as sarcomeres

  2. Are composed of proteins known as actin and myosin

  3. Are the actual contractile elements of the fibre

  4. All of the above

Show answer
Correct Option: D
Explanation:

  • Myofilament is the filaments of myofibrils, constructed from proteins, principally myosin or actin.
  • They are made up of thick and thin myofilament, which helps to give it a striped appearance.
So, the correct option is 'all of the above'.

State whether the following statements are true or false.
Actin is actually a globular protein that assembles as a long beady structure consisting of two helical chains.

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Skeletal muscle is composed of muscle fibres which have smaller units called myofibrils. There are three types of proteins make up each myofibril; they are contractile, regulatory and structural proteins. By contractile proteins, we mean actin (thin filament), a globular protein assembling with a long beady structure consisting chains and myosin (thick filament).

So, the correct option is 'True'.

The functional unit of myofibril is made up of

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. Complete A-band

  2. Complete I-band

  3. Complete I-band and two half A-band

  4. Complete A-band and two half I-band

Show answer
Correct Option: D

The proteins found in the filaments of muscle fibres are

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. Actin and myosin

  2. Myosin and elastin

  3. Actin only

  4. Myelin and tubulin

Show answer
Correct Option: A
Explanation:

Skeletal muscle is composed of muscle fibres which have smaller units called myofibrils. There are three types of proteins make up each myofibril; they are contractile, regulatory and structural proteins. By contractile proteins, we mean actin (thin filament) and myosin (thick filament).

So, the correct option is 'actin and myosin'.

The 'thick' filament in muscles is a polymerised protein of

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. meromyosins

  2. actins

  3. troponins

  4. tropomyosins.

Show answer
Correct Option: A

In the resting muscle fibre, tropomyosin partially covers

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. calcium binding sites on troponin

  2. actin binding sites on myosin

  3. myosin binding sites on actin

  4. calcium binding sites on actin.

Show answer
Correct Option: C
Explanation:

Tropomyosin is a protein found in the actin filaments in muscles. The molecule contains two elongated strands that run along the length of the filament. When the muscle is at rest, the tropomyosin molecule covers the binding site of the actin molecule, where interaction with myosin occurs, On contraction of the muscle, the tropomyosin is displaced by another protein, troponin, allowing the interaction of actin with myosin. So, the correct answer is (c).

Which of the following statements about the molecular arrangement of action and myosin in myofibrils is/are incorrect?
(i) Each actin (thin filament) is made of 2F (filamentous) actins.
(ii) F-actin is the polymer of G (globular) actin.
(iii) 2F-actins are twisted into a helix.
(iv) Two stands of tropomysion (protein) lie in the grooves of F-actin.
(v) Troponin molecurles (complex proteins) are distributed at regular intervals on the tropomyosin.
(vi) Troponin forms the head of the myosin molecule.
(vii) The myosin is a polymerised protein.

zoology locomotion and movement contractile protein structure of muscle muscles and their structure

  1. (i), (ii) and (vi)

  2. (ii), (iv) and (v)

  3. only (vi)

  4. only (iii)

Show answer
Correct Option: A
Explanation:

Following are the incorrect statements about the molecular arrangement of actin and myosin in myofibrils:

(i) Each actin (thin filament) is made of 2F (filamentous) actins.
(ii) F - actin is the polymer of G (globular) actin.
(iii) Troponin forms the head of the myosin molecule.
So, the correct answer is (a).