Which of the following ions binds to the troponin complex, initiating muscle contraction?
Potassium.
Calcium.
Phosphorus.
Sodium.
The Correct Answer is B
Calcium ions play a crucial role in initiating muscle contraction.
When a muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm.
Some of this calcium attaches to troponin, which causes it to change shape. This shape change exposes binding sites for myosin on the actin filaments.
Myosin’s binding to actin causes cross-bridge formation, and muscle contraction begins.
The other ions mentioned in the question do not have this specific role in muscle contraction.
Potassium ions are important for maintaining the resting membrane potential of cells, but they do not bind to the troponin complex.
Phosphorus ions are important for energy metabolism but do not bind to the troponin complex.
Sodium ions are important for generating action potentials but do not bind to the troponin complex.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
The best reason for the prolonged preservation of the body is that it was frozen in the cold temperature of the Alps shortly after he died and remained frozen until it was found.
Freezing can preserve a body by slowing down or stopping the decomposition process.
Choice A is not correct because the food that the person ate would not have contained toxins that killed the bacteria that would have otherwise destroyed the body.
Choice B is not correct because the arrow wound would not have caused blood to flow out of the body in a way that would have cleared enzymes that break down tissue from the body.
Choice D is not correct because ultraviolet rays at high altitude would not have caused all of the body’s molecules to be preserved.
Correct Answer is D
Explanation
Viruses lack the essential machinery needed to reproduce by themselves.
In fact, viruses can only reproduce after infecting a living cell - a process called viral replication.
Once inside a living cell, viruses re-program the cell’s machinery to produce viral proteins and genetic material to make new copies of themselves.
Choice A, Bacteria, is not the correct answer because bacteria have their own metabolic pathways and can reproduce outside of a host cell.
Choice B, Protozoa, is also not the correct answer because protozoa are single-celled eukaryotes that have their own metabolic pathways and can reproduce outside of a host cell.
Choice C, Helminths, is not the correct answer because helminths are multicellular parasitic worms that have their own metabolic pathways and can reproduce outside of a host cell.
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