A typical relaxed sarcomere is about 2.3 μm in length and contracts to about2 μm in length. Within the sarcomere, the thin filaments are about 1 μmlong and the thick filaments are about 1.5 μm 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 filamentabout 15 nm. How many steps must each actin fiber make in one contraction?

A typical relaxed sarcomere is about 2.3 μm in length and contracts to about2 μm in length. Within the sarcomere, the thin filaments are about 1 μmlong and the thick filaments are about 1.5 μm 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 filamentabout 15 nm. How many steps must each actin fiber make in one 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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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?
A typical relaxed sarcomere is about 2.3 um in length and contracts to about 2 um 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 con- tracted sarcomere. (b) An individual "step" by a myosin head in one cycle pulls the thin fila- ment about 15 nm. How many steps must each actin fiber make in one contraction?
Which of the following regions of a sarcomere at rest is characterized by the presence of myosin only? a) A band b) H zone c) I band d) Z line
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.
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…
28) the large protein that attaches to myosin and stabilizes it when the sarcomere shortens is: a) M line b) H zone c) I band d) A band
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
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.
Give typed explanation Put the events of a single cross-bridge cycle in the proper order. Start with Calcium is released from the sarcoplasmic reticulum. a) myosin binds to actin b) ATP binds to myosin, cross-bridge disconnect c) ATP splits into ADP and Pi d) Myosin head re-energized, repositions into high energy state e) Calcium resequestered into sarcoplasmic reticulum f) Cross-bridge power stroke g) Calcium binds to troponin , and actin binding sites are exposed
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 organization of myosin in smooth and striated muscle: A.) differ because smooth muscle lacks sarcomeres B.) is identical but the organization of actin is different C.) is identical but the isoforms of myosin differ D.) differ because striated muscle myosin forms filaments but smooth muscle myosin does not ATP is required for: a.) the phosphorylation of the myosin head in smooth muscle b.) the movement of tropomyosin on the actin filament c.) the swing of the myosin lever arm d.) A and B e.) tethering troponin I to troponin C
2) Paula is a scientist who is developing a drug called Fremtol that will be used to treat muscle spasms. This drug acts on specific skeletal muscles to (1) block the release of Ca2+ ions from the sarcoplasmic reticulum, (2) inhibit the pivoting ability of the myosin heads of the thick filaments, and (3) block the production of ATP by the mitochondria in skeletal muscles. By using this drug, contraction of certain skeletal muscle fibers is reduced, which keeps those muscles from producing spasms. In the above scenario, Fremtol’s effect of blocking the release of Ca2+ ions from the sarcoplasmic reticulum would most directly prevent which the following? a. activation of tropomyosin b. activation of troponin c. activation of actin d. All of the above e. None of the above