During the cross-bridge in muscle cells, myosin motors hydrolyzes ATP as a fuel to create a pulling force on actin fibers. Please describe 1) the myosin motors undergo different steps of ATP hydrolysis 2) the state of the ATP nucleotide affects the binding and position of the myosin motor with respect to the actin fiber

During the cross-bridge in muscle cells, myosin motors hydrolyzes ATP as a fuel to create a pulling force on actin fibers. Please describe 1) the myosin motors undergo different steps of ATP hydrolysis 2) the state of the ATP nucleotide affects the binding and position of the myosin motor with respect to the actin fiber

Human Physiology: From Cells to Systems (MindTap Course List)

9th Edition

ISBN:9781285866932

Author:Lauralee Sherwood

Publisher:Lauralee Sherwood

Chapter8: Muscle Physiology

Section: Chapter Questions

Problem 2TAHL

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As mentioned in class, one additional major use of ATP in skeletal muscle (besides powering the myosin heads) is the recycling of calcium ions back into the sarcoplasmic reticulum after depolarization. The resting concentration of Ca++ in the muscle cell cytoplasm is about 50-100 nM, and the spike concentration after depolarization is about 10-20 μΜ. a) Consider a single sarcomere. What is the number of free calcium ions within the sarcomere at rest? What is the number of free calcium ions after depolarization? b) The major ion pump responsible for calcium ion recycling is SERCA (sarco/endoplasmic reticulum calcium ATPase). SERCA uses one molecule of ATP to pump two calcium ions, and the resting level can be restored in about 10-20 ms. How many molecules of ATP are used in a single sarcomere for pumping calcium in a single "twitch"? c) Assume that a single "twitch" is sufficient to drive one sarcomere from its fully extended length (about 2.5 µm) to its fully contracted length (about 1…
The sliding-filament model of skeletal-muscle contraction assumes a sliding or slipping of interdigitating filaments of actin and myosin. Electron micrographs show that during contraction the actin and my-osin filaments remain of constant length while the distance between Z lines shortens. Explain how this happens in terms of the molecular structure of the muscle filaments. What is the role of regulatory pro-teins (troponin and tropomyosin) in contraction?
The ability of myosin to walk along an actin filament may be observed with the aid of an appropriately equipped microscope. Describe how such assays are typically performed. Why is ATP required in these assays? How can such assays be used to determine the direction of myosin movement or the force produced by myosin?
A few hours after the death of an animal, the corpse will stiffen as a result of continued contraction of muscle tissue (this state is called rigor mortis). This phenomenon is the result of the loss of ATP production in muscle tissue. (a) Consult Figure 7.48 and describe, in terms of the six-step model of mus- de contraction, how a lack of ATP in sarcomeres would result in rigor mortis. (b) The Ca* transporter in sarcomeres that keeps the [Ca*)-10-7 M requires ATP to drive transport of Ca* ions across the membrane of the sarcoplasmic reticulum. How would a loss of this Ca* transport func- tion result in the initiation of rigor mortis? (c) Rigor mortis is maximal at - 12 hrs after death, and by 72 hrs is no longer observed. Propose an explanation for the disappearance of rigor mortis after 12 hrs.
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Pluripotent stem cells undergo a number of changes as they progress through developmental stages to become the terminally differentiated cell type known as a skeletal muscle myofiber. a) Describe the stages and key anatomic and functional changes that occur during differentiation of myofibers. b) Despite the fact that myofibers are terminally differentiated, muscle can regenerate itself following a trauma or injury. Describe how this can occur.
During an experiment, the protein troponin from a skeletal muscle fiber was removed. This resulted in the permanent exposure of the actin binding site. Predict how cross-bridge cycling in this skeletal muscle fiber would be affected in the absence of troponin.
Describe the movement of myosin along an actin filament. Outline the primary molecular steps and explain how this process is used by cells. How many actin monomers within an actin filament would a myosin molecule need to ratchet in order to contract a cell by approximately 1 um? How fast could a non-muscle cell make this contraction compared to a muscle cell if the relative rates of myosin walks on F-actin are 4.5 um/sec and 0.04 um/sec for myosin II and I respectively?
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What is the reaction catalyzed by the ATPase domain of myosin?
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Discuss the steps in the hydrolysis of ATP by myosin and how these steps are coupled to the binding and unbinding of actin, promoting mechanical motion.