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[A] : Upon stimulation of a muscle cell...

[A] : Upon stimulation of a muscle cell, cal- cium ions `(Ca^(++))` are released from the sar- coplasmic reticulum.
[R]: In reacting with a protein complex, `Ca^(++)` unmasks myosin binding sites on the ac-tin filaments.

A

If both A and R are true and R is the correct explanation of A

B

If both A and R are true but R is not the correct explanation of A

C

If A is true and R is false

D

If both A and R are false

Text Solution

Verified by Experts

The correct Answer is:
B
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Assertion: on stimulation, a muscle cell releases calcium ions (Ca^(2+)) from sarcoplasmic reticulum. Reason: By reacting with a protien complex, Ca^(2+) uncover active sites on the actin filaments.

Which of the following statements given below are true with reference to muscle contraction. I. Neurotransmitter acetycholine is released as nerve impulse reaches the end of axon and binds to receptor sites of motor end plate. II. Action potential passes from motor end plate over sarcoplasmic and then into the T-tubules and sarcoplasmic reticulum. III. Calcium ion are released into the sarcoplasm bind to troponin, causing a change in its shape and position. IV. Myosin cross bridges are able to bind to exposed active sites of actin. Choose the correct option.

The steps involved in the mechanism of muscle contraction are given below. Arrange the steps in proper sequential order and select the correct option. I. Release of calcium ions in the sarcoplasm. II. Signal sent by the CNS via a motor neuron. III. Binding of calcium with a subunit of troponin on actin filaments. IV. Generation of the action potential in the sarcolemma. V. Binding of myosin head to the exposed active sites on actin to form a cross-bridge. VI. Inward pulling of ‘Z’ line attached to actin causing shortening of the sarcomere. VII. Pulling of the attached actin filaments towards the centre of 'A' band. VIII. Release of neurotransmitter acetylcholine and generation of the action potential in the sarcolemma.

Go through the following statements During muscle contraction, the width of A-band remains constant while I-band shortens. During muscle contraction, the Ca^(2+) released from the SR bind to the troponin component of thin filament The process of muscle contraction is faster in smooth muscle as they have a well developed sarcoplasmic reticulum. The red muscle fibres have abundant mitochondria, low glycogen and poorly formed sarcoplasmic reticulum.

Read the following statements (i) In cardiac muscle fibres sacroplasmic reticulum is poorly formed (ii)B Blood supply is scanty in case of smooth muscle fibres (iii) Tropomyosin occurs in actin filaments in the form of complexes which are arranged over actin fibres and represent sites where myosin binds to actin. (iv) Salts of citrate and oxalates act as anticoagulants as they precipitate Ca^(2+) Select the correct statements

Assertion : - Ca^(++) play an important role in the muscle contraction. Reason :- Calcium bind with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin.

Select the total number of false statement from the following (i) The globular head is an active ATPase enzyme and has binding sites for ATP and active sites for Myosin. (ii) Each Myosin (think) filament is also a polymerized protine. (iii) Many monomeric proteins celled Meromyosins canstitute one thick filament. (iv) Each meromyosin has two important parts, a globular head with a short arm and a til, the former being Called the heavy meromyosin (HMA) and the latter, the light meromysin (LMN). (v) The HMM component, i.e., the head and short arm projects outwards at regular distance and angle from each other from the surface of a polymerized myosis filament and is known as cross arm

This ion is responsible for unmasking of active sites for myosin during muscle contraction? (A) "K^(+) (B) "Mg^(2+) (C) Ca(2+) (D) "Na^(+)

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