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.

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.

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 2SQE

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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 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?
With regard to muscle contraction, which of the following is an INCORRECT statement with regard to the interactions of filaments that occur in the sarcomere? A. When muscles are relaxed tropomyosin blocks binding sites on actin subunits, which keeps cross-bridges from forming. B. The myosin heads conduct a power stroke motion to slide when bound to actin, to move the "thin" filaments towards the center of the sarcomere. C. During contraction, actin subunits are removed from the ends of the "thin" filaments to shorten actin polymers, thus reducing the length of the sarcomere. D. "Thick" filaments are anchored at the M-line, while "thin" filaments are anchored at the Z-line. E. Numerous myosin heads engage with the actin filaments simultaneously, such that there is no back-slipping during the contraction process.
Myosin II action differs from that of kinesin in that one of the kinesin heads is always in contact with a microtubule, whereas both myosin heads become completely detached from the actin ﬁlament. How are these differences correlated with the two types of motor activities in which these proteins engage?
In the sliding filament theory of contraction, what prevents the filaments from sliding back to their original positions each time a myosin head releases to bind to next actin binding site?
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?
Why is myosin II the only myosin capable of producing contractile force?
Which of these statements about the molecular structure of myofilaments is true?a. Tropomyosin has a binding site for Ca2+.b. The head of the myosin molecule binds to an active site on G actin.c. ATPase is found on troponin.d. Troponin binds to the rodlike portion of myosin.e. Actin molecules have a hingelike portion, which bends and straightensduring contraction.
When ADP and Pi are bound to myosin in the cross-bridge cycle... (MULTIPLE SELECT) A. There is no force production and myosin is not bound to actin B. There is no force production and myosin is bound to actin C. There is force production and myosin is not bound to actin D. If its smooth muscle, a second phosphate might be bound to the light chain E. The cross-bridge is in a state of rigor mortis F. There is force production and myosin is bound to actin
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In bending in the binding of the myosin head of the free binding site of the actin filament results in the contraction of the muscle
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