Which does NOT depict a way in which Ca2+ ions regulate muscle contraction? Sele

Question

Which does NOT depict a way in which Ca2+ ions regulate muscle contraction? Select one: Actin microfilaments become dissociated from tropomyosin and troponin following Ca2+-binding. Ca2+-binding regulates the tread milling function of actin microfilaments. Depolarization of the resting membrane potential of a muscle fiber increases cytosolic Ca2+ levels. None of these statements accurately depict the role of Ca2+ ions in muscle contraction. Microtubules are important for transporting cargo in nerve ell axons, as diagrammed in the figure. Notice that the two types of cargo (black and grey) are traveling in opposite directions. Which of the following statements is FALSE? The black cargo and the grey cargo are moving along microtubules of opposite polarity. The black cargo and the grey cargo require ATP hydrolysis of their motion. The black cargo moving toward the axon terminal is attached to the tail domain of a motor protein. The grey cargo is attached to dynein. Which of the following would NOT constitute a question germane to the completion of the cell cycle? Are the conditions favorable for cell growth and proliferation? Is all of the DNA free of any damage? Has all of the DNA been replicated at least one or more times? Are all of the chromosomes correctly aligned at the metaphase plate?

Explanation / Answer

1. b

troponin and tropomyosin are proteins of actin thin filaments. they bind to actin and block the myosin binding sites of actin. upon calcium binding, they dissociate and allow actin to bind with myosin.

depolarization of skeletal muscle causes opening of voltage gated calcium channels and allows influx of extracellular calcium into cytoplasm.

2. a (most probably)

polarity plays an important role in determining the direction of movement along microtubules. it decides the orientation of microtubules in axons i.e, plus ends oriented away from cell body. but may be bo role in transporting molecules.

in vitro experiments demonstrated that fast axonal transport requires energy from ATP hydrolysis.

kinesin proteins move cargoes from cell body to tip. the cargoes are attached to the tail domain of kinesins.

dynein proteins help in retrograde transport i.e, towards cell body. grey cargoes are moving towards cell body and thus assisted by dyneins.

3. c

DNA will be replicated only once per cell cycle. so the question should be " has all the DNA been replicated?"

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