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Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892

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BuyFindarrow_forward

Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

During contraction of skeletal muscle:

a. ATP stimulates Ca2+ to move out of the cytosol, which allowstropomyosin to bind myosin causing contraction of the thinfilament.

b. myosin crossbridges use ATP to relax the molecular spring in the myosin head, which pulls the thick filaments away from the thin actin filaments.

c. actin binds ATP, allowing troponin in the thick filaments toform the myosin crossbridge.

d. action potentials cause the release of Ca2+ allowingtropomyosin fibers to uncover the actin binding sites neededfor the myosin crossbridge.

e. botulinum toxin could increase the release of acetylcholine at the contracting muscle site.

Summary Introduction

Introduction:

The sliding filament model explains that the precise control of muscle contraction starts with action potentials traveling down an efferent neuron through a signaling pathway that causes muscle contractions, which are responsible for the body motions. These neural signals carry information from nerves to muscle fibers and trigger contractions.

Explanation

Justification for the correct answer:

Option (d) states that the action potentials cause the release of Ca2+ allowing tropomyosin fibers to uncover the actin binding sites needed for the myosin crossbridge. According to the sliding filament contractile mechanism, when Ca2+ flows into the cytosol and binds to the troponin molecules of the actin thin filament, a conformational change takes place. This allows the tropomyosin fibers to slide into the grooves of the actin double helix, thus, uncovering the actin’s binding sites for the myosin crossbridge. Hence, option (d) is correct.

Justification for the incorrect answers:

Option (a) states that the sliding filament contractile mechanism is inhibited by the influx of Ca2+ into the muscle fiber cytosol. It is not a true statement as it is in contradiction to the actual process explained above. So, it is an incorrect option.

Option (b) states that the myosin crossbridges use ATP (adenosine triphosphate) to relax the molecular spring in the myosin head, which pulls the thick filaments away from the thin actin filaments...

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