4. Myosin myopathies are a suite of diseases caused by genetic mutation of the myosin head in muscle myosin filaments. Affected people experience muscle weakness that may lead to the inability to climb and lift as well as a waddling gait. Armel and Leinwand (2009) stated that "Mutations in the myosin head are thought to affect the ATPase and actin- binding properties of the molecule." Use a diagram to explain the possible consequences of mutations in the myosin head on muscle activity and their link with the symptoms of affected people. 3
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Step 1: The myosin head is a crucial component of muscle myosin filaments that is responsible for interacting with actin filaments during muscle contraction. Show more…
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Describe how the thin actin filament and the myosin head of a thick filament interact during one contraction cycle by arranging the steps below in the correct order. In this case, assume the following: ATP has just bound to a myosin head, causing the myosin head to dissociate from the thin filament in a sarcomere. Ca2+ is bound to the regulatory protein troponin on the thin filaments so that troponin has changed shape and pulled the tropomyosin filament away from the myosin binding sites on actin. For this question, you will use each answer once and only once. Step 1: [Choose] Step 2: [Choose] Step 3: [Choose] Step 4: [Choose] Step 5: [Choose] Step 6: [Choose] Step 7: [Choose]
Supreeta N.
An abundant myosin-family member, myosin $\mathrm{V}$ is isolated from brain tissue. This myosin has a number of unusual properties. First, on the basis of its amino acid sequence, each heavy chain has six tandem binding sites for calmodulin-like light chains. Second, it forms dimers but not higher-order oligomers. Finally, unlike almost all other myosin-family members, myosin V is highly processive. The rate of ATP hydrolysis by myosin has been examined as a function of ATP concentration, as shown in graph A. (FIGURE CAN'T COPY) (a) Estimate the values of $k_{\text {cat }}$ and $K_{\mathrm{M}}$ for ATP. With the use of optical-trap measurements, the motion of single myosin V dimers could be followed, as shown in graph B. (FIGURE CAN'T COPY) (b) Estimate the step size for myosin V. The rate of ADP release from myosin V is found to be approximately 13 molecules per second. (c) Combine the observations about the amino acid sequence of myosin, the observed step size, and the kinetics results to propose a mechanism for the processive motion of myosin V.
The myosin head is bound to ATP, ADP, and Pi when it is in the low energy conformation, and it is bound to the thin filament. No nucleotide. The myosin head is bound to ADP and Pi when it is in the extended, high energy conformation. ATP, ADP, and Pi. The myosin head is bound to ADP and Pi during the power stroke. Cross-bridge formation occurs when the myosin head is bound to no nucleotide. ADP and Pi. The absence of ATP would prevent the myosin head from detaching from the thin filament. The myosin head is bound to ATP when it is in the low energy conformation and is not bound to the thin filament.
Adi S.
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