BIOL 201 Lecture 14: Myosin & Muscle

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19 Apr 2018

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Motor proteins are responsible for converting chemical energy like atp into mechanical work. Myosin can translocate actin filaments across a glass slide. Myosin ii forms bundles that pull the filaments inward causing the muscle cell to shorten/contract. Muscles are made of billions of contractile bundles of muscle fibers. Within each muscle fiber, there is a multinucleated muscle cell. Myoblasts fuse together to form one long multinucleated cell. Within a cross section of each multinucleated cell, there are a large number of myofibrils. Within each myofibril, you have a structure known as a sarcomere. The defining boundaries of a sarcomere are known as z disk. Myosin filaments located within the dark region (thick filaments) & actin filaments rils. nts. Myosin filaments located within the dark region (thick filaments) & actin filaments are in the light region (thin filaments). Are the basic unit of the sliding filament theory. When a muscle is stretched, z disks would be the furthest apart.

Related Questions

1)Describe the directions in which the two motor proteins, kinesin and dynein, travel along a microtubule. Which of the two proteins moves materials towards the Golgi and which moves materials away from the Golgi? Lastly, what is the speed of kinesin dependent on?

2)What are microfilaments crucial for? How do they self-assemble? Which end do they prefer to elongate from?

3)Describe what types of filaments are in each of the bands of the sarcomere. As a muscle fiber is shortened, describe what happens to each of the bands in the sarcomere as the Z lines move inwards.

4)Describe the role of calcium ions in muscle contraction.

5)List the various types of actin-binding proteins

6) A. What are 3 functions of the cytoskeleton?

B.What are the three filaments that compose the cytoskeleton, and what are they composed?

7)How do they see the internal structures of cells in the microscope? What do proteins get labeled with?

8)Myosin II action (Figure 9.61) differs from that of kinesin (Figure 9.15) 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?

9)If a myofibril were pulled so that the sarcomeres increased in length by approximately 50 percent, what effect would you expect this to have on the contractile ability of the myofibril? Why? What effects would this have on the H, A, and I bands?

10)Because cytoplasmic vesicles are seen to move in both directions within an axon, can you conclude that some microtubules are oriented with their plus end facing the axon terminus and others oriented with the opposite polarity? Why or why not?

1. Each muscle fiber is a bundle of myofibrils. Eachmyofibril is a series of sarcomeres. Thus, a muscle fiber contractswhen each sarcomere within a series contracts simultaneously. Suchcoincidence is mirrored by each myobril within the muscle fiber.What enables the extent to which molecular motors contractsimultaneously within an innervated muscle fiber?

a. the frequency of acetylcholine secretion within theneuromuscular synapse

b. the frequency of Ca²⁺ oscillations within themuscle fiber

2. A living muscle fiber experiences dynamic frequencies ofCa²⁺ oscillations. In effect, Ca²⁺ acts as asecond messenger when it disperses throughout the fluid-filledspaces between actin and myosin filaments. What is the source ofthis second message?

a. extracellular fluid b.sarcoplasmic reticulum

3. Why might a muscle fiber need an ample amount ofNa⁺,K⁺-ATPase on itssurface?

a. as evident by the value of the cellâs membrane potential,muscle fibers are leaky to Na⁺

b. to counter the effect of numerous action potentials persecond

4. Assume that you could âseeâ nicotinic acetylcholine receptorswithin the musculature. How would they be arranged spatially?

a. evenly distributed on the cellâs surface like voltage-gatedNa⁺ and K⁺ channels

b. in dense arrays within the motor end plate

5. Assume that you could âseeâ neurosecretion fromÎ±-motor neurons within the musculature of an animal standing still.What would this âlookâ like?

a. uniform, baseline secretion throughout the musculature

b. enhanced acetylcholine secretion within antigravity muscles,baseline secretion elsewhere

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BIOL 201 Lecture 14: Myosin & Muscle

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