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 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?

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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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?
Certain multi-headed myosins bind cooperatively to actin filaments. The binding interaction is mainly electrostatic in nature, so the presence of additional salt (ions) in solution can interfere with binding; ions will tend to associate with charged residues on the two proteins, blocking electrostatic attractions that would otherwise take place. Briefly describe the expected shape of the binding curve for one of these myosins, and what will happen to the shape when the salt concentration increases.
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…
Myosin II has a duty ratio of 10 percent, and its step size is 8 nm. In contrast, myosin V has a much higher duty ratio (about 70 percent) and takes 36-nm steps as it walks down an actin filament. What differences between myosin II and myosin V account for their different properties?
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?
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.
During the cross-bridge in muscle cells, myosin motors hydrolyzes ATP as a fuel to create a pulling force on actin fibers. Please describe1) the myosin motors undergo different steps of ATP hydrolysis2) the state of the ATP nucleotide affects the binding and position of the myosin motor with respect to the actin fiber
A typical relaxed sarcomere is about 2.3 µm in length and contracts to about 2 µm in length. Within the sarcomere, the thin filaments are about 1 um long and the thick filaments are about 1.5 um long. (a) Describe the overlap of thick and thin filaments in the relaxed and contracted sarcomere. (b) An individual "step" by a myosin head in one cycle pulls the thin filament about 15 nm. How many steps must each actin fiber make in one contraction?
What is the main order histological structure of sarcomere? * Z line bind with actine without interaction with myosin Interaction of actine and myosin with Z line Interaction of myosin and actine with Z line Interaction of Z line with myosin and actine
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.
1. a) Why are muscles not in a contracted state all the time? b) Several hours after the death of an animal, a state of rigor mortis, extreme rigidity of the body, occurs. With respect to myosin and actin filaments, why does this occur? What causes the body to relax more later in time? Explain.
Skeletal muscle cells undergo contractions based on a molecular mechanism involving: 1)the sliding of actin and myosin filaments past each other without any change in filament length 2) the shortening of actin filaments following direct interaction with myosin 3) dynamic instability of microtubules 4)none