1. The plasma membrane of liver cells contains a glucose uniport that transports
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Question
1. The plasma membrane of liver cells contains a glucose uniport that transports glucose by facilitated diffusion. When the [glucose] is higher inside the liver cell than the [glucose] outside the liver cell, the glucose uniport will
A. couple the transport of glucose out of the cell to the hydrolysis of ATP
B. couple the transport of glucose into the cell to the hydrolysis of ATP
C. switch to a closed conformation, allowing no transport of glucose
D. transport glucose out of the cell by passive transport
E. transport glucose in of the cell by passive transport
2. Unlike the positive charged ion shown in the middle diagram of figure 11-4B, K+ is higher in concentration inside the cell. How will the membrane potential of a cell at rest (shown in both the middle and right-hand diagrams of Figure 11-4B) affect the electrochemical gradient for K+?
A. The membrane potential will increase the electrochemical gradient
B. The membrane potential will decrease the electrochemical gradient
C. The membrane potential will have no effect on the electrochemical gradient
3. Which of the following proteins carries out active transport?
A. gluclose symport
B. Bacteriorhodopsin
C. ABC transporter
D. NA K pump
E. All of the above
4. Aquaporin will not transport Na+ ions because
A. Two asparagine residues in the channel prevent the passage of Na+ ions by binding the oxygen of each water molecule as it passes by
B. Na+ ions are repelled by the positive charges at the entrance to the channel
C. Na+ ions cannot make contact with the carbonyl (C=O) groups on all four sides of the channel
D. The passage of Na+ ions is energetically unfavorable because one side of the channel is hydrophobic in nature
5. The acetylcholine receptor is different from other channel proteins we have discussed, such as the K+ leak channel, because
A. The acetylcholine channel is composed of a single polypeptide rather than multiple subunits
B. The acetylcholine channel transports Na+ ions against the concentration gradient for sodium
C. The acetylcholine channel has a much smaller diameter than other channel proteins
D. The acetylcholine channel transports ions with their associated shell of water molecules
E. The acetylcholine channel is always open, and never switches to a closed conformation
6. After opening briefly along the axon of a neuron, voltage-gated ion channels switch to an inactivated conformation that slowly returns to the original closed conformation of the protein. This slow change in conformation, requiring about a millisecond, is important because
A. all of the ions that were transported across the membrane when the ion channels were open must be actively transported back to the other side of the membrane, restoring the original concentration gradient, before the ion channels can open again
B. ATP hydrolysis is necessary to drive this energetically unfavorable change in conformation
C. it prevents the action potential from reversing direction and traveling back toward the cell body of the neuron
D. the channel protein must be dephosphorylated in order to complete the transport process and return to the original nonphosphorylated conformation
Explanation / Answer
1.
Uniport is a passive transporter that is involved in transport of sugars and amino acids. Glucose uniport is the transporter, which is specific to glucose and transports glucose by facilitated diffusion in liver, erythrocytes, and other cells.
If glucose concentration is high outside the cell when compared to inside, then the glucose binds to a site on outside of protein and is transported into the cell by a process called passive diffusion. In contrast, if glucose concentration is high inside the cell when compared to outside, then the glucose binds to an inside site of protein and is transported out the cell by a process called passive diffusion.
Hence, the correct option among the following is D.
2.
Membrane potential is defined as the voltage difference across the plasma membrane.
In the given case, it is stated that the concentration of potassium ions is high inside
Hence, the correct option among the following is B.
3.
The active transport requires energy in the form of ATP. In this case, the molecules move against the concentration gradient and require carrier protein.
Hence, the correct option among the following is E.
4.
Aquaporins are the channels that are involved in flow of water through cell membrane. The factors that hinder the transport of ions through channels are membrane potential and concentration gradient.
Hence, the correct option among the following is E.
5.
The correct option among the following is B.
6.
The correct option among the following is C.
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