Nokea
At the skeletal muscle sarcomere, Ca2+ ions do each of the following, except:
- A. Bind to troponin to help uncover tropomyosin
- B. Help expose active sites on actin strands
- C. Is stored in the sarcoplasmic reticulum at terminal cisternae
- D. Helps break the ATP into ADP + inorganic phosphate readying the myosin head to bind another active site
Correct Answer: d
Rationale: Rationale for Correct Answer (D):
1. Ca2+ ions do not directly break down ATP into ADP + inorganic phosphate at the sarcomere.
2. This breakdown occurs through the enzymatic action of myosin ATPase.
3. Ca2+ ions primarily bind to troponin to initiate muscle contraction by moving tropomyosin.
4. Ca2+ ions help expose active sites on actin, facilitating cross-bridge formation.
Summary of Incorrect Choices:
A. Correct - Ca2+ binds to troponin to move tropomyosin, not to uncover it.
B. Correct - Ca2+ aids in exposing active sites on actin, not troponin.
C. Correct - Ca2+ is stored in the sarcoplasmic reticulum, but it is released into the cytoplasm to trigger muscle contraction, not stored in the terminal cisternae.
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- A. parathyroid hormone
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Correct Answer: B
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- A. Nodules.
- B. Islets of Langerhans.
- C. Pancreatic medulla.
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Correct Answer: B
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Why are the hormones cortisol, glucagon, epinephrine, and growth hormone referred to as counter regulatory hormones?
- A. Decrease glucose production
- B. Stimulate glucose output by the liver
- C. Increase glucose transport into the cells
- D. Independently regulate glucose level in the blood
Correct Answer: B
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Peptide hormones _______________.
- A. are hydrophilic
- B. cannot enter the target cell
- C. bind to a receptor on the cell surface
- D. all of these
Correct Answer: D
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