BIOLOGY:CONCEPTS+APPL.(LOOSELEAF)
10th Edition
ISBN: 9781305967359
Author: STARR
Publisher: CENGAGE L
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Chapter 32, Problem 2CT
After death, a person no longer makes ATP, so calcium stored in the sarcoplasmic reticulum diffuses down its concentration gradient into the muscle cytoplasm. This result is rigor mortis----an unbreakable state of muscle contraction that stiffens the body for a few days until muscles begin to decay. Explain why this contraction occurs.
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You are a brilliant (but evil) biochemist who is developing a toxin that can be used to paralyze skeletal muscle. Using your knowledge of how muscle contraction happens at the cellular and molecular levels, identify two steps in the sequence of events necessary for the contraction that could be disrupted to cause paralysis, and explain why each disruption would prevent muscle contraction.
After death, a person no longer makes ATP, and calcium stored in the specialized endoplasmic reticulum of muscle fibers diffuses down its concentration gradient into the muscle cytoplasm. The result is rigor mortis—an unbreakable state of muscle contraction. Explain why the contraction occurs and why it is irreversible.
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…
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- 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 abovearrow_forwardImpairment of intracellular calcium homeostasis in muscle fibers lead to chronic, severe muscle dysfunction. Impaired Calcium ATPase activity can lead to abnormal, persistent elevation of intracellular calcium concentrations. Explain how persistently high intracellular calcium concentration would affect cross-bridge formation, and muscle contractions, and muscle tension? (Mention the effects on the steps involved cross bridge formation, and muscle contraction/relaxation cycle, and overall muscle tension).arrow_forwardIn muscle cells, magnesium ions compete with calcium ions for binding sites on troponin molecules. If a person has too high a concentration of magnesium ions in the blood, magnesium ions can prevent calcium ions from binding troponin. A) What effect would this have on muscle contraction (strengthen, weaken, or no effect)? B) Use your knowledge of how muscle fibers contract to explain your answer in part A.arrow_forward
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