Chapter 12
9 Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell? (a) Na+ (b) K+ (c) Ca2+ (d) Cl-
(a) Na+
41 Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding 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 and 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.
(a) Some channels remain closed and some open completely.
59 The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions? (a) acetylcholine (b) glutamate (c) GABA (d) glycine
(a) acetylcholine
17 Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________. (a) active transport. (b) free diffusion. (c) facilitated diffusion. (d) passive transport.
(a) active transport.
2 Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found? (a) an aquaporin (b) a sodium channel (c) a calcium channel (d) a proton channel
(a) an aquaporin
5 We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which of the following has the lowest rate of diffusion across an artificial membrane? Why? (a) glucose (b) water (c) glycerol (d) ethanol
(a) glucose
16 Transporters, in contrast to channels, work by ________________. (a) specific binding to solutes. (b) a gating mechanism. (c) filtering solutes by charge. (d) filtering solutes by size.
(a) specific binding to solutes.
27 You have generated antibodies that recognize the extracellular domain of the Ca2+-pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+? (a) Ca2+-pumps in vesicle membranes keep cytosolic calcium levels low. (b) Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low. (c) Ca2+-pumps in the Golgi apparatus keep cytosolic calcium levels low. (d) Ca2+ concentrations in the cytosol increase at a steady rate.
(b) Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low.
3 Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion? (a) HCO3- (b) Cl- (c) PO43- (d) OH-
(b) Cl-
14 Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? Explain your answer. (a) Mg2+ (b) H+ (c) K+ (d) Cl-
(b) H+
36 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.
(b) It opens more frequently in response to a given stimulus.
8 Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell? (a) Na+ (b) K+ (c) Ca2+ (d) Cl-
(b) K+
20 Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is not one of the common ways to perform active transport? (a) Na+-coupled (b) K+-coupled (c) ATP-driven (d) light-driven
(b) K+-coupled
62 Which of the following statements best reflects the nature of synaptic plasticity? (a) New synapses are created due to the postnatal generation of neurons. (b) Synaptic response changes in magnitude depending on frequency of stimulation. (c) There is a change in the type of neurotransmitter used at the synapse. (d) Neuronal connections are pruned during normal development.
(b) Synaptic response changes in magnitude depending on frequency of stimulation.
45 When using the Nernst equation to calculate membrane potential, we are making several assumptions about conditions in the cell. Which of the following is not a good assumption? (a) The temperature is 37°C. (b) The plasma membrane is primarily permeable to Na+. (c) At rest, the interior of the cell is more negatively charged than the exterior. (d) K+ is the principal positive ion in the cell.
(b) The plasma membrane is primarily permeable to Na+.
35 Which of the following occur without coupling transport of the solute to the movement of a second solute? (a) import of glucose into gut epithelial cells (b) export of Ca2+ from the cytosol (c) export of H+ from animal cells for pH regulation (d) the export of Na+ from cells to maintain resting membrane potential
(b) export of Ca2+ from the cytosol
30 Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for _____________. (a) maintaining osmotic balance. (b) preventing Ca2+ from altering the activity of molecules in the cytosol. (c) providing enzymes in the endoplasmic reticulum with Ca2+ ions that are necessary for their catalytic activity. (d) maintaining a negative membrane potential.
(b) preventing Ca2+ from altering the activity of molecules in the cytosol.
10 Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following negatively charged ions is not primarily used to buffer positive charges inside the cell? (a) PO43- (b) OH- (c) Cl- (d) HCO3-
(c) Cl-
46 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.
(c) It becomes more positive.
42 When the net charge on either side of the plasma membrane is zero, what else is true? (a) There is an equal number of K+ ions on each side of the plasma membrane. (b) The K+ leak channels are open. (c) The electrochemical potential across the membrane is zero. (d) The resting membrane potential is between -20 mV and -200 mV.
(c) The electrochemical potential across the membrane is zero.
12 Which of the following statements about resting membrane potential is not true? (a) The resting membrane potential for most animal cells is 0 mV, because the positive and negative ions are in balance. (b) The resting membrane potential for most animal cells is positive, because Na+ ions are so plentiful inside cells. (c) The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell. (d) At the resting membrane potential, no ions enter or exit the cell.
(c) The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell.
66 Which of the following gated ion channels are involved in inhibitory synaptic signaling? (a) voltage-gated Na+ channels (b) voltage-gated Ca2+ channels (c) glycine-gated Cl- channels (d) glutamate-gated cation channels
(c) glycine-gated Cl- channels
15 Some cells have aquaporins—channels that facilitate the flow of water molecules through the plasma membrane. For these cells, what regulates the rate and direction of water diffusion across the membrane? (a) aquaporin conformation (b) resting membrane potential (c) solute concentrations on either side of the membrane (d) availability of ATP
(c) solute concentrations on either side of the membrane
21 The Na+-K+ ATPase is also known as the Na+-K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP? (a) Na+ is bound (b) ADP is bound (c) the pump is phosphorylated (d) the pump changes conformation
(c) the pump is phosphorylated
63 Approximately, how many distinct synapses are established on the dendrites and cell body of a motor neuron in the spinal cord? (a) tens (b) hundreds (c) thousands (d) millions
(c) thousands
11 Negatively charged ions are required to balance the net positive charge from metal ions such as K+, Na+, and Ca2+. Which of the following negatively charged ions is the most abundant outside the cell and which ion does most often neutralize (written in parentheses)? (a) Cl- (Ca2+) (b) PO43- (K+) (c) PO43- (Ca2+) (d) Cl- (Na+)
(d) Cl- (Na+)
28 Cells make use of H+ electrochemical gradients in many ways. Which of the following proton transporters is used to regulate pH in animal cells? (a) light-driven pump (b) H+ ATPase (c) H+ symporter (d) Na+-H+ exchanger
(d) Na+-H+ exchanger
48 In a method called patch-clamping, a glass capillary can be converted into a microelectrode that measures the electrical currents across biological membranes. Which of the following is not true about the patch-clamp method? (a) The glass capillary adheres to a "patch" of membrane through the application of suction. (b) The aperture in the glass capillary used to make a microelectrode is about 1 μm in diameter. (c) If the experimental conditions are held constant, fluctuations in electrical currents across the patch of membrane are still observed. (d) Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.
(d) Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.
29 Which of the following statements is true? (a) Amoebae have transporter proteins that actively pump water molecules from the cytoplasm to the cell exterior. (b) Bacteria and animal cells rely on the Na+-K+ pump in the plasma membrane to prevent lysis resulting from osmotic imbalances. (c) The Na+-K+ pump allows animal cells to thrive under conditions of very low ionic strength. (d) The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.
(d) The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.
51 Which of the following statements does not accurately describe the events involved in the propagation of an action potential? (a) An initial influx of Na+ through a small cluster of channels causes local depolarization of the membrane. (b) Local depolarization causes nearby Na+ channels to open. (c) Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished. (d) The opening of transmitter-gated K+ channels helps to repolarize the membrane.
(d) The opening of transmitter-gated K+ channels helps to repolarize the membrane.
43 K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell? (a) They set the K+ concentration gradient to zero. (b) They set the membrane potential to zero. (c) They disrupt the resting membrane potential. (d) They keep the electrochemical gradient for K+ at zero.
(d) They keep the electrochemical gradient for K+ at zero.
64 Which of the following statements about GABA receptors is not true? (a) They are located on postsynaptic membranes. (b) They are ligand-gated channels. (c) They inhibit synaptic signaling. (d) They promote neuronal uptake of Na+.
(d) They promote neuronal uptake of Na+.
60 Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential? (a) by closing Na+ channels (b) by preventing the secretion of excitatory neurotransmitters (c) by opening K+ channels (d) by opening Cl- channels
(d) by opening Cl- channel
6 Below is a list of molecules with different chemical characteristics. Knowing that all molecules will eventually diffuse across a phospholipid bilayer, select the option below that most accurately predicts the relative rates of diffusion of these molecules (fastest to slowest). alanine estrogen propanol sodium (a) alanine > propanol > sodium > estrogen (b) sodium > propanol > alanine > estrogen (c) estrogen > propanol > sodium > alanine (d) estrogen > propanol > alanine
(d) estrogen > propanol > alanine
13 A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell's demise? (a) toxic buildup of carbon dioxide inside the cell (b) toxic buildup of ethanol inside the cell (c) diffusion of ATP out of the cell (d) inability to import sugar into the cell
(d) inability to import sugar into the cell
39 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
(d) stress-gated
52 Which of the following is required for the secretion of neurotransmitters in response to an action potential? (a) neurotransmitter receptors (b) Na+-K+ pumps (c) voltage-gated K+ channels (d) voltage-gated Ca2+ channels
(d) voltage-gated Ca2+ channels
7 A molecule moves down its concentration gradient by __________________ transport, but requires __________________ transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a __________________ pathway through the membrane for specific polar solutes or inorganic ions. __________________ are highly selective in the solutes they transport, binding the solute at a specific sterm-18ite and changing conformation so as to transport the solute across the membrane. On the other hand, __________________ discriminate between solutes mainly on the basis of size and electrical charge. active, hydrophilic, passive, ion channels, transporter proteins
A molecule moves down its concentration gradient by _passive_ transport, but requires _active_ transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a _hydrophilic_ pathway through the membrane for specific polar solutes or inorganic ions. _Transporter proteins_ are highly selective in the solutes they transport, binding the solute at a specific site and changing conformation so as to transport the solute across the membrane. On the other hand, _ion channels_ discriminate between solutes mainly on the basis of size and electrical charge.
38 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Gap junctions are large pores that connect the cytosol to the extracellular space. B. Aquaporin channels are found in the plasma membrane, and allow the rapid passage of water molecules and small ions in and out of cells. C. The ion selectivity of a channel depends solely on the charge of the amino acids lining the pore inside the channel. D. Most ion channels are gated, which allows them to open and close in response to a specific stimulus, rather than allowing the constant, unregulated flow of ions.
A. False. Gap junctions are used to connect the cytosol of adjacent cells, allowing the sharing of ions and small metabolites. Because gap junctions are large channels, if they were open while facing the extracellular environment, the ability of the plasma membrane to serve as a permeability barrier would be greatly reduced. B. False. Charged molecules (even protons, which are very small) are not able to pass through aquaporins. C. False. Selectivity depends on three parameters: the diameter, shape, and charge of the ion trying to pass through the pore of the channel. D. True.
18 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient. B. Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied. C. The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient. D. The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter.
A. False. This describes coupled transport, which is one type of active transport. Facilitated diffusion can also be called passive transport, in which a solute always moves down its concentration gradient. B. True. C True. D. False. Glucose is an uncharged molecule, and its import is not directly affected by the voltage difference across the membrane if glucose is being transported alone. If the example given were the Na/glucose symporter, we would have to consider the charge difference across the membrane.
50 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane. B. Action potentials are usually mediated by voltage-gated Ca2+ channels. C. Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon. D. Voltage-gated K+ channels also open immediately in response to local depolarization, reducing the magnitude of the action potential.
A. True. B. False. Action potentials are usually mediated by voltage-gated Na+ channels. C. True. D. False. Voltage-gated K+ channels respond more slowly than the voltage-gated Na+ channels. Because voltage-gated K+ channels do not open until the action potential reaches its peak, they do not affect its magnitude. Instead, they help to restore the local membrane potential quickly while the voltage-gated Na+ channels are in the inactivated conformation.
1 Indicate whether the following statements are true or false. If a statement is false, explain why it is false. A. CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes. B. The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content. C. Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them. D. Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell.
A. True. B. False. The primary difference between cell membranes and artificial membranes is that cell membranes have proteins responsible for creating a selective permeability, which varies with the location and function of the membrane. C. False. Transporters work by changing conformation after specific binding of the solute to be transported. Channels exclude molecules on the basis of size and charge, but do not depend on specific recognition of the molecules moving through. D. True.
26 Indicate whether the statements below are true or false. If a statement is false, explain why it is false. A. The extracellular concentration of Ca2+ is approximately 104-fold higher than the concentration of Ca2+ in the cytosol. B. The low cytosolic Ca2+ concentration sensitizes the cell to an influx of Ca2+, ensuring a rapid response to environmental stimuli. C. Cytosolic Ca2+ concentration is kept low by the use of chelators such as EDTA. D. The primary mechanism by which Ca2+ acts as a signaling molecule is by increasing the net charge in the cytosol.
A. True. B. True. C False. Ca2+ concentrations in the cytosol are kept low by the action of ATP-driven calcium pumps in the endoplasmic reticulum membrane and the plasma membrane. D. False. Ca2+ binds tightly to many proteins in the cell, which in turn changes their activity. This interaction is the primary mechanism by which Ca2+ signaling occurs.
4 Circle the molecule in each pair that is more likely to diffuse through the lipid bilayer. A. amino acids or benzene B. Cl- or ethanol C. glycerol or RNA D. H2O or O2 E. adenosine or ATP
A. benzene (small nonpolar versus larger uncharged) B. ethanol (polar versus charged) C. glycerol (small polar versus very large, highly charged) D. O2 (nonpolar versus polar) E. adenosine (polar versus highly charged)
40 For each of the following sentences, fill in the blank with the appropriate type of gating for the ion channel described. A. The acetylcholine receptor in skeletal muscle cells is a(n) _________ ion channel. B. _________ ion channels are found in the hair cells of the mammalian cochlea. C. _________ ion channels in the mimosa plant propagate the leaf-closing response. D. _________ ion channels respond to changes in membrane potential. E. Many receptors for neurotransmitters are _________ ion channels.
A. ligand-gated B. stress-gated C. voltage-gated D. voltage-gated E. ligand-gated
22 If ATP production is blocked in an animal cell, the cell will swell up. Explain this observation.
ATP is required to power the Na+-K+ pump, which is necessary for maintaining osmotic balance. The pump requires ATP hydrolysis to drive its pumping cycle. So, in the absence of ATP production, the Na+ concentration inside the cell will increase. This is followed by passive diffusion of water across the membrane, causing the cell to swell.
19 It is thought that the glucose transporter switches between two conformational states in a completely random fashion. How is it possible for such a system to move glucose across the membrane efficiently in a single direction?
Although the opening of the glucose transporter on one side of the membrane or the other is random, the binding of glucose into the binding site of the transporter is not a random event. The affinity between the glucose molecule and the transporter governs the binding event: transporter + glucose ↔ transporter-glucose At high glucose concentrations, the complex formation is favored; at low glucose concentrations, dissociation of glucose from the transporter is favored. So, as long as there is a large concentration gradient, efficient transport can occur by the simple rules of binding equilibria.
31 For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its __________________ gradient. On the other hand, for a charged molecule, the __________________ must also be considered. The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the __________________ gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called __________________ transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute. When this transporter moves both ions in the same direction across the membrane, it is considered a(n) __________________; if the ions move in opposite directions, the transporter is considered a(n) __________________. antiport, coupled, membrane potential, electrochemical, symport, concentration,
For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its "concentration" gradient. On the other hand, for a charged molecule, the "membrane potential" must also be considered. The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the "electrochemical' gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called "coupled" transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute. When this transporter moves both ions in the same direction across the membrane, it is considered a "symport"; if the ions move in opposite directions, the transporter is considered an "antiport."
34 Describe the process by which gut epithelial cells use transporters to take up ingested glucose (against the concentration gradient) and to distribute glucose to other tissues by moving it back out of the cell (down the concentration gradient).
Gut epithelial cells use two different transporters to take glucose up from the gut and distribute it into the bloodstream and to other tissues. These transporters are located at opposite sides of the cell: the apical side of the cell (which faces the gut) contains a Na+glucose symporter. This symporter couples the entry of Na+ down its electrochemical gradient to the active import of glucose against its concentration gradient. The Na+glucose symporter is restricted to the apical side of the cell by tight-junction complexes in the plasma membrane, which link neighboring epithelial cells together. On the basolateral side of the cell, there is another transporter that facilitates movement of glucose down its concentration gradient, out of the cell. This transporter is a uniporter that only transports glucose in one direction: from the cytosol to the extracellular matrix. The location of this uniporter is also restricted by the presence of the tight junctions, so that the epithelial cell will not transport glucose back into the lumen of the gut.
58 The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. How is the chemical signal converted into an electrical signal in the postsynaptic muscle cell?
Most neurotransmitter receptors function as ligand-gated ion channels. These ion channels are similar to voltage-gated channels, except that they do not open in response to a change in voltage across the membrane, but to the binding of a neurotransmitter. In the neuromuscular junction, the neurotransmitter acetylcholine binds to the acetylcholine receptor, which allows Na+ to enter the muscle cell, altering its membrane potential. In this way, a chemical signal (acetylcholine) is converted back into an electrical signal (change in membrane potential).
61 Neurons communicate with each other through specialized sites called __________________. Many neurotransmitter receptors are ligand-gated ion channels that open transiently in the __________________ cell membrane in response to neurotransmitters released by the __________________ cell. Ligand-gated ion channels in nerve cell membranes convert __________________ signals into __________________ ones. Neurotransmitter release is stimulated by the opening of voltage-gated __________________ in the nerve-terminal membrane. postsynaptic, Ca2+ channels, presynaptic, chemical, synapses, electrical
Neurons communicate with each other through specialized sites called "synapses." Many neurotransmitter receptors are ligand-gated ion channels that open transiently in the "postsynaptic" cell membrane in response to neurotransmitters released by the "presynaptic" cell. Ligand-gated ion channels in nerve cell membranes convert "chemical" signals into "electrical" ones. Neurotransmitter release is stimulated by the opening of voltage-gated "Ca2+ channels" in the nerve-terminal membrane.
57 The action potential is a wave of __________________ that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is __________________ negative than the resting membrane potential. The action potential is propagated by the opening of __________________gated channels. During an action potential, the membrane potential changes from __________________ to __________________. The action potential travels along the neuron's __________________ to the nerve terminals. Neurons chiefly receive signals at their highly branched __________________. axon, less, positive, dendrites, depolarization, negative, voltage
The action potential is a wave of "depolarization" that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is "less" negative than the resting membrane potential. The action potential is propagated by the opening of "voltage"-gated channels. During an action potential, the membrane potential changes from "negative" to "positive". The action potential travels along the neuron's "axon" to the nerve terminals. Neurons chiefly receive signals at their highly branched "dendrites".
32 The movement of glucose into the cell, against its concentration gradient, can be powered by the co-transport of Na+ into the cell. Explain this movement with respect to the net entropy of the system (that is, thermodynamics).
The movement of Na+ ions from an area that has a high Na+ concentration to a new area of low Na+ concentration is energetically favorable because the net entropy in the system is increasing. As long as the difference in Na+ ion concentration across the membrane is large, the entropic factor will be sufficient to drive the import of glucose into the cell, which represents a decrease in entropy with respect to the population of glucose molecules inside the cell.
65 Describe how synaptic signaling is influenced by the action of tranquilizers (such as Valium®) compared to the effects of antidepressants (such as Prozac®).
Tranquilizers promote inhibitory signaling at the synapse. They do this by making GABA-gated channels open more easily in response to the inhibitory neurotransmitter GABA. This channel, when open, allows Cl- to flow into the neuron, making the cell more difficult to depolarize. Antidepressants are used to enhance the neuronal signaling in neurons that have serotonin receptors. Prozac® specifically blocks the reuptake of serotonin in the synaptic cleft. This results in a net increase in serotonin available for excitatory signaling to the postsynaptic neuron.
