18. Which of the following best describes the behavior of a gated channel? (a) i

Question

18. Which of the following best describes the behavior of a gated channel?
(a) it stays open continuously when stimulated
(b) it opens more frequently in response to a given stimulus
(c) it opens more widely as the stimulus becomes stronger
(D) it remains closed if unstimulated
19. The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use?
(a) voltage gated
(b) extracellular ligand gated
(c) intracellular ligand gated
(d) stress gated
20. Voltage gated channels contain charged protein domains, which are sensitive to changes in the membrane potential. By responsding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold?
(a) some channels remain closed ans some open completely
(b) all channels open completely
(c) all channels open partly, to the same degree
(d) all channels open partly, each to a different degree
21. If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected?
(a) the membrane potential is not affected by Na+
(b) it becomes more negative
(c) it becomes more positive
(D) it is permanently reset.
22. Neurotransmitter are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane (a) TRUE (b) FALSE
23. Action potentials are usually mediated by voltage gated Ca2+ channels (a) TRUE (b) FALSE
24. Voltage gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon (a) TRUE (b) FALSE
25. voltage gated K+ channels also open immediated in response to local depolarization, reducing the magnitude of the action potential (a) TRUE (b) FALSE
26. Most proteins destined to enter the endoplasmic reticulum _______.
(a) are transported across the membrane after their synthesis is complete
(b) are synthesized on free ribosomes in the cytosol
(c) begin to cross the membrane while still being synthesized
(d) remain within the endoplasmic reticulum
27. In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins?
(a) the nucleus
(b) on the rough ER
(c) in the cytosol
(d) in the lumen of the ER
28. What is the role of the nuclear localization sequence in a nuclear protein?
(a) it is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore
(b) it is a hydrophobic sequence that enables the protein to enter the nuclear membranes
(c) it aids in protein unfolding so that the protein can thread through nuclear pores
(d) it prevents the protein from diffusing out of the nucleus through nuclear pores.

Explanation / Answer

18. (d) Remain closed if unstimulated 19. (a) voltage-gated 20. (b) channels open completely 21. (c) the membrane potential becomes more positive 22. (b) false 23. (a) true 24. (a) true 25. (b) false 26. (c) enter the ribosome as they are being synthesized 27. (c) in the cytosol 28. (a) bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore I am confident about these answers.

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