Cell Bio Exam 3 (ch 11-14)

In this illustration of the structure of ATP synthase, which of the components rotate? Choose one or more: 1 2 3 4 5

1 5

Assume five molecules of FADH2 are made in the citric acid cycle in a given amount of time. How many NADH are made during the same time interval?

15

Most of the energy released by oxidizing glucose is saved in the high-energy bonds of what molecules? Choose one: H2O and CO2 GDP and other activated carriers O2 ATP and other activated carriers ADP and other activated carriers

ATP and other activated carriers

Mutation in the hemoglobin gene can cause sickle-cell anemia. The defective protein found in sickle-cell anemia causes red blood cells to "sickle"—become a misshapen C shape. These misshapen cells abnormally stick to each other and can become trapped by leukocytes (white blood cells) that are rolling or paused on the endothelial cells lining the vessel. This causes blockages of small blood vessels, causing severe pain and strokes called vaso-occlusive crisis. A new drug that binds and blocks selectin proteins is in phase III clinical trials to test for improvement in patients' symptoms. Why might this be an effective treatment for vaso-occlusive crisis? Choose one: A. Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells. B. Blocking selectins would block the ability of selectin to bind carbohydrates on the surface of red blood cells, preventing the blockage. C. Blocking selectins would reduce activation of pain sensors in the blood vessels. D. Blocking selectins on red blood cells would prevent the red blood cells from binding to the blood vessel endothelial cells, preventing the blockage of red blood cells.

A. Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells.

Which of the following is supported by the information in the figure? Choose one or more: A. Sodium and potassium are involved in co-transport. B. Nucleotides enter the cell by facilitated diffusion. C. Glucose enters the cell by simple diffusion.

A. Sodium and potassium are involved in co-transport. B. Nucleotides enter the cell by facilitated diffusion.

Which of the following statements correctly describe an aspect of converting light to chemical energy in chloroplasts? Choose one or more: A. The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space. B. Photosystem II is used to produce NADPH directly from NADP+ and two electrons. C. Light excites electrons in photosystem II only. D. Excited electrons are passed through an electron transport chain.

A. The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space. D. Excited electrons are passed through an electron transport chain.

Which organelle is important for controlling the concentration of calcium ions in the cytosol? Choose one: A. endoplasmic reticulum B. Golgi apparatus C. lysosome D. nucleus

A. endoplasmic reticulum

A group of researchers wanted to sort different white blood cell types (monocytes, lymphocytes, and granulocytes) apart from each other based on size differences and to remove unwanted contaminating red blood cells. After a particular manipulation, the red blood cells lysed. The remaining white blood cells increased in size and, more importantly, the size differences among cells increased, allowing for size-based sorting (which requires minimum size differences among cells). What manipulation did the researchers use to increase cell size? Choose one: A. placing cells in an environment with a lower solute concentration than that in the cells B. placing cells in an environment with a higher solute concentration than that in the cells C. placing cells in an environment with lower temperatures than the cells were previously exposed to D. patch-clamp recording to monitor ion channel activity

A. placing cells in an environment with a lower solute concentration than that in the cells

The drug 2,4-dinitrophenol (DNP) makes the mitochondrial inner membrane permeable to H+. The resulting disruption of the proton gradient inhibits the mitochondrial production of ATP.What additional effect would DNP have on the transport of ATP out of the mitochondrial matrix? Choose one: ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane. None, because ATP export is not coupled to the movement of protons across the inner membrane. None, because the inner membrane is permeable to ATP. ATP transport will decrease because less ATP will be available to diffuse across the inner membrane. ATP transport will increase because ATP synthase will be forced to operate in the "reverse" direction.

ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane.

Antimycin A is a piscicide (fish poison) used to manage fisheries and kill invasive species. Antimycin A blocks the transfer of electrons through the cytochrome b-c1 complex. What components of the electron transport chain are bound to high-energy electrons after treating a mitochondrion with antimycin A? Choose one: A. All three complexes and NADH are bound to high-energy electrons. B. NADH and the NADH dehydrogenase complex are bound to high-energy electrons while O2 and the cytochrome c oxidase complex are not. C. None of the complexes are bound to high-energy electrons. D. O2 and the cytochrome c oxidase complex are bound to high-energy electrons while NADH and the NADH dehydrogenase complex are not.

B. NADH and the NADH dehydrogenase complex are bound to high-energy electrons while O2 and the cytochrome c oxidase complex are not.

The FRAP technique occurs in a series of steps. Select every statement that correctly describes a step in the FRAP procedure. Choose one or more: A. The speed of repair of the fluorescent marker is measured. B. The relative mobility of the fluorescently labeled molecule is measured. C. The molecule of interest is fluorescently labeled. D. All fluorescent molecules in the cell are irreversibly bleached.

B. The relative mobility of the fluorescently labeled molecule is measured. C. The molecule of interest is fluorescently labeled.

Your friends are on a low-fat, high-carbohydrate diet, which they claim will prevent fat accumulation within their bodies. They eat tons of pasta and bread without worrying about calorie count. What can you correctly say to your friends about their potential to accumulate lipids on their low-fat diet? Choose one: A. They will not accumulate fats because cells have no way of storing fats. B. They will accumulate fats because cells can convert glycolytic metabolites into lipids. C. They will not accumulate fats because carbohydrates have less energy per gram than fats. D. They will accumulate fats because cells have no way of storing carbohydrates.

B. They will accumulate fats because cells can convert glycolytic metabolites into lipids.

Sodium ions, oxygen (O2), and glucose pass directly through lipid bilayers at dramatically different rates. Which of the following choices presents the correct order, from fastest to slowest? Choose one: A. glucose, oxygen, sodium ions B. oxygen, glucose, sodium ions C. sodium ions, oxygen, glucose D. glucose, sodium ions, oxygen E. oxygen, sodium ions, glucose

B. oxygen, glucose, sodium ions

Which of the following characteristics of K+ channels are important for the selectivity for K+ rather than other ions? Choose one or more: A. Acidic side chains line the wall of the pore. B. Basic side chains line the wall of the pore. C. Carbonyl groups line the wall of the pore. D. Four rigid protein loops line the narrowest part of the pore.

C. Carbonyl groups line the wall of the pore. D. Four rigid protein loops line the narrowest part of the pore.

Ions in solution are found in a hydration shell of water. This shell must be removed for an ion to pass through the channel. How does the K+ channel accomplish removal of the water from the shell around the ion? Choose one: A. The K+ channel has four subunits; one subunit removes the hydration shell as the ion passes through the pore formed by the three other subunits. B. Rigid protein loops strip the hydration shell from the potassium so that the ion is the right diameter to pass through the pore. C. Carbonyl groups lining the wall of the pore can interact with the unsolvated K+ ion, balancing the energy needed to remove the hydration shell. D. The K+ channel uses the energy in ATP hydrolysis to remove the hydration shell from the K+ ion.

C. Carbonyl groups lining the wall of the pore can interact with the unsolvated K+ ion, balancing the energy needed to remove the hydration shell.

Weight loss can occur when glucose is oxidized to CO2 rather than being stored as glycogen. The first step in glucose oxidation is glycolysis. A 1930s diet drug, DNP, made the inner mitochondrial membrane permeable to protons, increasing the rate of glycolysis. What is the explanation for the DNP-induced increase in glycolysis? Choose one: A. High ATP activates phosphofructokinase. B. High AMP inhibits phosphofructokinase. C. High ADP activates phosphofructokinase. D. DNP also makes the inner mitochondrial membrane leaky to glucose, increasing the ability of the mitochondria to perform glycolysis.

C. High ADP activates phosphofructokinase.

This technique has clinical uses. For example, some individuals with high blood pressure (hypertension) have a genetic defect in an epithelial Na+ channel (ENaC) that makes the channel hyperactive (open more than normal). Such individuals can be treated with amiloride, which inhibits sodium ion movement through ENaC. Researchers predicted that amiloride would not effectively treat hypertension in individuals with normal ENaC activity and tested this prediction by analyzing ENaC activity in patch-clamped cells from individuals with high blood pressure, some of whom showed hyperactive ENaC and some of whom showed normal ENaC activity. Which of the following results align with researcher expectations? Choose one or more: A. Patch-clamp data showed hyperactive ENaC prior to amiloride treatment; patient did not benefit from amiloride. B. Patch-clamp data showed normal ENaC activity prior to amiloride treatment; patient benefited from amiloride. C. Patch-clamp data showed hyperactive ENaC prior to amiloride treatment; patient benefited from amiloride. D. Patch-clamp data showed normal ENaC activity prior to amiloride treatment; patient did not benefit from amiloride.

C. Patch-clamp data showed hyperactive ENaC prior to amiloride treatment; patient benefited from amiloride. D. Patch-clamp data showed normal ENaC activity prior to amiloride treatment; patient did not benefit from amiloride.

Why would a cell express the aquaporin protein if water can cross the membrane in the absence of aquaporin? Choose one: A. Aquaporin moves a positively charged ion along with water across the membrane. B. Aquaporin limits the movement of water molecules so they do not move too quickly across the membrane. C. Water molecules cannot cross the membrane in the absence of a pore like aquaporin. D. Aquaporin facilitates the faster movement of water molecules across the membrane.

D. Aquaporin facilitates the faster movement of water molecules across the membrane.

You join a laboratory to study muscle function. You decide to inhibit the pumping of Ca2+ into the sarcoplasmic reticulum to determine how excess cytosolic Ca2+ will affect muscle function. Which of the following strategies would be effective in blocking Ca2+ pumping? Choose one: A. block the hydrolysis of ATP to AMP by the Ca2+ pump B. enhance the binding of ATP to the Ca2+ pump C. block binding of ATP to the pump in the lumen of the sarcoplasmic reticulum D. block the phosphorylation of the conserved aspartate in the Ca2+ pump

D. block the phosphorylation of the conserved aspartate in the Ca2+ pump

How do transporters and channels select which solutes they help move across the membrane? Choose one: A. Channels will allow the passage of any solute as long as it has an electrical charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate. B. Both channels and transporters discriminate between solutes mainly on the basis of size and electric charge. C. Transporters discriminate between solutes mainly on the basis of size and electric charge; channels bind their solutes with great specificity in the same way an enzyme binds its substrate. D. Channels allow the passage of solutes that are electrically charged; transporters facilitate the passage of molecules that are uncharged. E. Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.

E. Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.

For voltage-gated channels, a change in the membrane potential has what effect on the channel? Choose one: A. It changes which ions can pass through the channel. B. It makes the channel more sensitive to the binding of neurotransmitters. C. It changes the width of the channel opening. D. It either opens the channel or closes it, depending on the voltage. E. It alters the probability that the channel will be found in its open conformation.

E. It alters the probability that the channel will be found in its open conformation.

When ATP and food molecules such as fatty acids are abundant, which will occur? Choose one: Enzymes involved in glycolysis will operate in the reverse direction, using pyruvate to produce glucose. Enzymes involved in glycolysis will break down glucose to generate pyruvate. When food and ATP are plentiful, both glycolysis and gluconeogenesis will occur. Enzymes involved in gluconeogenesis will use energy to produce glucose. When food molecules are plentiful, neither glycolysis nor gluconeogenesis will occur.

Enzymes involved in gluconeogenesis will use energy to produce glucose.

Experiments performed by Hans Krebs in the 1930s revealed that the set of reactions that oxidize food molecules and produce CO2 occur in a cycle. In one experiment, Krebs exposed pigeon muscles to malonate, a compound that inhibits succinate dehydrogenase—the enzyme that converts succinate to fumarate, indicated in red in the linear representation of the reactions of the citric acid cycle (below).Which of the following observations, made in malonate-treated muscle, led Krebs to believe that this set of reactions is cyclical? Choose one: If citrate were added, succinate would accumulate. Regardless of what he added, oxaloacetate would accumulate. If succinate were added, fumarate would accumulate. If fumarate were added, succinate would accumulate. Regardless of what he added, large amounts of oxygen would be produced.

If fumarate were added, succinate would accumulate.

When scientists were first studying the fluidity of membranes, they did an experiment using hybrid cells. Certain membrane proteins in a human cell and a mouse cell were labeled using antibodies coupled with differently colored fluorescent tags. The two cells were then coaxed into fusing, resulting in the formation of a single, double-sized hybrid cell. Using fluorescence microscopy, the scientists then tracked the distribution of the labeled proteins in the hybrid cell.Which best describes the results they saw and what they ultimately concluded? Choose one: Initially, the mouse and human proteins intermixed, but over time, they were able to resegregate into distinct membrane domains. This suggests that cells can restrict the movement of membrane proteins. The mouse and human proteins remained confined to the portion of the plasma membrane that derived from their original cell type. This suggests that cells can restrict the movement of their membrane proteins to establish cell-specific functional domains. The mouse and human proteins began to intermix and spread across the surface of the hybrid cell, but over time, one set of proteins became dominant and the other set was lost. This suggests that cells can ingest and destroy foreign proteins. Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins recombined such that they all fluoresced with a single, intermediate color. Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer. At first, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became divided such that half faced the cytosol and half faced the hybrid cell exterior. This suggests that flippases are activated by cell fusion.

Initially, the mouse and human proteins were confined to their own halves of the newly formed hybrid cell, but over time, the two sets of proteins became evenly intermixed over the entire cell surface. This suggests that proteins, like lipids, can move freely within the plane of the bilayer.

What happens to the ATP produced during stage 1 of photosynthesis? Choose one: It is consumed within the chloroplast to fuel electron transport. It is exported from the chloroplast to fuel the plant's metabolic needs. It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate. It is exported from the chloroplast and used to produce sucrose. It is consumed within the chloroplast to produce NADPH.

It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.

Which statement is true of glycogen phosphorylase? Choose one: It stimulates gluconeogenesis. It is inhibited by glucose 6-phosphate, but activated by ATP. It is inhibited by glucose 6-phosphate and by ATP. It is activated by glucose 6-phosphate, but inhibited by ATP. It is activated by glucose 6-phosphate and by ATP.

It is inhibited by glucose 6-phosphate and by ATP.

In most animal cells, which ion can move through "leak" channels? Choose one: Ca2+ H+ Cl- Na+ K+

K+

Although the citric acid cycle itself does not use O2, it requires a functioning electron transport chain (which uses O2) in order to regenerate which molecule for further use in the citric acid cycle? Choose one: ATP FADH2 NAD+ NADH ADP

NAD+

What would be the consequences to NADPH production if the redox potential of pC (plastocyanin) were altered to be more negative than the redox potential of cytochrome b6-f? Choose one: NADPH production would halt since pC would no longer accept electrons from the cytochrome b6-f complex, blocking the electron transport chain. NADPH production would not be altered since NADPH is produced from photosystem I. NADPH production would be higher since pC would be a better electron donor. NADPH would be broken down since the electron transport chain would work backward.

NADPH production would halt since pC would no longer accept electrons from the cytochrome b6-f complex, blocking the electron transport chain.

Lipid bilayers are highly impermeable to which molecule(s)? Choose one: water Na+ and Cl- oxygen steroid hormones carbon dioxide

Na+ and Cl-

In eukaryotic cells, what is the final electron acceptor in the electron transport chain? Choose one: ATP FADH2 CO2 O2 NAD+

O2

Below is a table listing the reactions that constitute the 10 steps of glycolysis, along with the change in free energy (ΔG°) for each step. Based on the data, which steps in glycolysis are effectively irreversible? Choose one: Steps 6 and 7 Steps 5, 7, 8, and 9 Step 1 Steps 1, 3, and 10 Steps 1, 3, 7, and 10 Steps 1, 2, 3, 4, 6, and 10

Steps 1, 3, and 10

In 1925, scientists exploring how lipids are arranged within cell membranes performed a key experiment using red blood cells. Using benzene, they extracted the lipids from a purified sample of red blood cells. Because these cells have no nucleus and no internal membranes, any lipids they obtained were guaranteed to come from the plasma membrane alone.The extracted lipids were floated on the surface of a trough filled with water, where they formed a thin film. Using a movable barrier, the researchers then pushed the lipids together until the lipids formed a continuous sheet only one molecule thick.The researchers then made an observation that led them to conclude that the plasma membrane is a lipid bilayer.Which of the following would have allowed the scientists to come to this conclusion? Choose one: The extracted lipids covered the same surface area as the intact red blood cells. The extracted lipids covered half the surface area of the intact red blood cells. The extracted lipids covered twice the surface area of the intact red blood cells. When pushed together, the extracted lipids dissolved in water.

The extracted lipids covered twice the surface area of the intact red blood cells.

When the transport vesicle shown below fuses with the plasma membrane, which monolayer will face the cell cytosol? Choose one: It depends on whether the vesicle is coming from the endoplasmic reticulum or the Golgi apparatus. It depends on the cargo the vesicle is carrying. Half the time the orange monolayer will face the cytosol, and half the time the blue monolayer will face the cytosol. The orange monolayer will face the cytosol. The blue monolayer will face the cytosol.

The orange monolayer will face the cytosol.

In a patch of animal cell membrane about 10 μm in area, which will be true? Choose one: There will be more proteins than lipids. There will be about an equal number of proteins and lipids. There will be more carbohydrates than lipids. Because the lipid bilayer acts as a two-dimensional fluid, there is no way to predict the relative numbers of proteins and lipids in any patch of cell membrane. There will be more lipids than proteins.

There will be more lipids than proteins.

How do enzymes maximize the energy harvested from the oxidation of food molecules? Choose one: They allow the stepwise oxidation of food molecules, which releases energy in small amounts. They allow a larger amount of energy to be released from food molecules such as glucose. They guarantee that each reaction involved in the oxidation of food molecules proceeds in just one direction. They allow what would otherwise be an energetically unfavorable oxidation reaction to occur. They allow oxidation reactions to take place without an input of activation energy.

They allow the stepwise oxidation of food molecules, which releases energy in small amounts.

Which two-carbon molecule enters the citric acid cycle? Choose one: pyruvate citrate oxaloacetate acetyl CoA carbon dioxide

acetyl CoA

The movement of an ion against its concentration gradient is called what? Choose one: osmosis passive transport facilitated diffusion active transport

active transport

In cells, pyruvate can be converted to which of the following? Choose one or more: alanine lactate acetyl CoA glucose oxaloacetate

alanine lactate acetyl CoA glucose oxaloacetate

The proton gradient that drives ATP synthesis during photosynthesis is generated by which of the following? Choose one: an electron carrier that removes electrons from water an electron carrier that pumps protons out of the thylakoid space into the stroma an electron carrier that pumps protons out of the stroma into the thylakoid space an electron carrier that receives electrons from photosystem I the operation of two photosystems that work in series

an electron carrier that pumps protons out of the stroma into the thylakoid space

The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following? Choose one: eukaryotic cells cells that could pump protons multicellular life hydrothermal vents cells that could use the energy of sunlight to produce NADPH

cells that could pump protons

What determines the direction that glucose is transported across the membrane, through a glucose transporter? Choose one: concentration gradient a molecule's size a molecule's charge membrane potential

concentration gradient

What is the voltage difference across a membrane of a cell called? Choose one: electrical current gradient establishment potential balance membrane potential

membrane potential

Where does the oxidative (oxygen-dependent) stage of the breakdown of food molecules occur in a eukaryotic cell? Choose one: Golgi apparatus mitochondrion cytosol endoplasmic reticulum

mitochondrion

Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA? Choose one or more: oxaloacetate GTP NAD+ ATP O2 GDP

oxaloacetate NAD+ O2 GDP

The NADH generated during glycolysis and the citric acid cycle feeds its high-energy electrons to which of the following? Choose one: the electron transport chain the citric acid cycle ADP FAD H2O

the electron transport chain

In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step? Choose one: the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate the transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP the reversible rearrangement of glucose 6-phosphate to fructose 6-phosphate

the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate

What does the term "gluconeogenesis" refer to? Choose one: the release of glucose from molecules such as glycogen the breakdown of glucose during fermentation the breakdown of glucose during glycolysis the transport of glucose across a cell membrane the synthesis of glucose from small organic molecules such as pyruvate

the synthesis of glucose from small organic molecules such as pyruvate

Why must all living cells carefully regulate the fluidity of their membranes? Choose one or more: to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules to allow cells to function at a broad range of temperatures to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell to constrain and confine the movement of proteins within the membrane bilayer to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides

to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides

In what form do plant and animal cells store fat? Choose one: glycogen phospholipids nitroglycerin triacylglycerol starch

triacylglycerol

When a neuron is activated by a stimulus, its plasma membrane will change until it reaches a membrane potential of about +40 mV. What is special about this value? Choose one: A. It is approximately the membrane potential at which the electrochemical gradient for Na+ is zero. B. It is the threshold potential that opens voltage-gated Na+ channels. C. It is the threshold potential at which voltage-gated Na+ channels close. D. It is approximately the membrane potential at which the electrochemical gradient for K+ is zero. E. It is the opposite of the resting membrane potential.

A. It is approximately the membrane potential at which the electrochemical gradient for Na+ is zero.

What is the name of the specialized junction between a neuron and a target cell? Choose one: A. synapse B. axon C. dendrite D. nerve terminal E. synaptic vesicle

A. synapse

Which of the following mechanisms prevents osmotic swelling in plant cells? Choose one: A. tough cell walls B. the activity of Na+ pumps C. the collection of water in contractile vacuoles D. turgor pressure E. the expulsion of water from contractile vacuoles

A. tough cell walls

Which statements below accurately describe an aspect of the citric acid cycle? Choose one or more: A. The citric acid cycle produces two kinds of high-energy molecules, GTP and NADH. B. Oxaloacetate is regenerated by the end of the citric acid cycle. C. NADH is generated in steps 3, 4, and 8. D. The two carbons that enter as acetyl CoA are released in the same cycle as CO2.

B. Oxaloacetate is regenerated by the end of the citric acid cycle. C. NADH is generated in steps 3, 4, and 8.

Protons are pumped across the mitochondrial inner membrane as electrons are transferred through the mitochondrial electron transport chain. Which of the following statements about proton pumping are correct? Choose one or more: A. Protons are pumped into the matrix of the mitochondria. B. The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane. C. The mitochondria use the proton gradient to synthesize ATP. D. The pH inside the mitochondrial matrix is higher than in the intermembrane space.

B. The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane. C. The mitochondria use the proton gradient to synthesize ATP. D. The pH inside the mitochondrial matrix is higher than in the intermembrane space.

During the activation of a neuron, the action potential propagates in only one direction. How is this achieved in the neuron? Choose one: A. The Na+ channel closes during the action potential and then rapidly returns to the open state after the action potential passes. B. The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes. C. The Na+ channel remains open during the action potential and then rapidly returns to the closed state after the action potential passes. D. The Na+ channel becomes permanently inactivated after the action potential passes.

B. The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes.

In the technique called optogenetics, light-gated Na+ channels are introduced into the brains of living animals. Activation of these channels by light can depolarize the membranes of neurons that contain them, selectively activating these target cells.Since its inception, optogenetics has been expanded to include other types of light-gated channels, such as a channel that is selective for Cl- instead of Na+. If this light-gated Cl- channel were introduced into neurons in a region of the brain that stimulates feeding, what might you expect to see? Choose one: A. In response to light activation, the animals would overeat, even when they are full. B. The animals would avoid eating, even when they are hungry—but only when the channels are activated by light. C. The channels would have no effect on behavior because the animal's normal Na+ channels would allow normal depolarization of neurons that regulate feeding. D. The animals would avoid eating, even when they are hungry. E. The animals would avoid eating, but only during the day.

B. The animals would avoid eating, even when they are hungry—but only when the channels are activated by light.

Your friend now has the pumps successfully pumping ions. She added an equal concentration of both ions to the correct sides of the liposomes along with an excess of the energy source. She is surprised when the pumps stop working after a short time. Which of the following could explain why the transporter stopped pumping ions? Choose one: A. The liposomes ran out of pumps to pump ions. B. The pump ran out of Na+ to pump because it pumps 3 Na+ out for every 2 K+ pumped in. C. The pump ran out of K+ to pump because it pumps 3 K+ out for every 2 Na+ pumped in. D. The pump ran out of both Na+ and K+ because an equal number of both ions is pumped in each cycle.

B. The pump ran out of Na+ to pump because it pumps 3 Na+ out for every 2 K+ pumped in.

Antibiotics should inhibit bacterial cell growth without generating side effects in the human patient, but that is not always the case. Some antibiotics that inhibit bacterial protein synthesis by binding to bacterial ribosomes induce negative side effects in patients. What is the most likely cause of these side effects? Choose one: A. The antibiotics interfere with chloroplast ribosomes. B. The antibiotics interfere with ribosomes attached to the ER, impairing RER function. C. The antibiotics interfere with mitochondrial ribosomes. D. The antibiotics interfere with cytoplasmic ribosomes.

C. The antibiotics interfere with mitochondrial ribosomes.

The epithelial cells that line the gut have glucose-Na+ symport proteins that actively take up glucose from the lumen of the gut after a meal, creating a high glucose concentration in the cytosol. How do these cells release that glucose for use by other tissues in the body? Choose one: A. The cells have glucose channels in their plasma membrane. B. The cells have a glucose pump that expels the glucose needed by other tissues. C. The cells have glucose uniports in their plasma membrane. D. Glucose diffuses down its concentration gradient through the lipid bilayer of the plasma membrane. E. The cells run the glucose-Na+ symport proteins in reverse.

C. The cells have glucose uniports in their plasma membrane.

Which of the following characteristics of aquaporins ensure that the channel selectively transports only water molecules and not other solutes? Choose one or more: A. The channel undergoes conformational changes to push water through the channel. B. A glutamate at the entrance to the channel prevents positive ions from entering the channel. C. The channel has a narrow pore that is only wide enough for a single water molecule to pass through. D. Two asparagines in the center of the pore prevent protons from passing through the channel.

C. The channel has a narrow pore that is only wide enough for a single water molecule to pass through. D. Two asparagines in the center of the pore prevent protons from passing through the channel.

Which membrane would show a more rapid recovery of fluorescence in a FRAP study? Choose one: A. a membrane containing a large amount of cholesterol B. The saturation of fatty acids in a cell membrane does not affect the speed of fluorescence recovery in a FRAP study. C. a membrane containing a larger proportion of unsaturated fatty acids D. a membrane containing a larger proportion of saturated fatty acids E. a membrane containing equal amounts of saturated and unsaturated fatty acids

C. a membrane containing a larger proportion of unsaturated fatty acids

When a neuron has been stimulated by a signal, the change in membrane potential first spreads locally to adjoining regions of the plasma membrane by what means? Choose one: A. action potential B. active transport C. passive spread D. opening of ligand-gated ion channels E. opening of voltage-gated ion channels

C. passive spread

Carbon fixation occurs in the second stage of photosynthesis, during the light-independent reactions of the Calvin cycle. In the first step of this cycle, the enzyme Rubisco adds CO2 to the energy-rich compound ribulose 1,5-bisphosphate, ultimately producing two molecules of 3-phosphoglycerate. In a culture of green alga that is carrying out photosynthesis in the presence of CO2 in the laboratory, what would happen to the levels of ribulose 1,5-bisphosphate and 3-phosphoglycerate in the minutes after the lights were turned off and the cultures were plunged into darkness? Choose one: Ribulose 1,5-bisphosphate would accumulate, but 3-phosphoglycerate would be depleted. Both would be depleted. Nothing would happen because the Calvin cycle is not light-dependent. Both would accumulate. Ribulose 1,5-bisphosphate would be depleted, but 3-phosphoglycerate would accumulate.

Ribulose 1,5-bisphosphate would be depleted, but 3-phosphoglycerate would accumulate.

Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell. How might a cell actively engineer this phospholipid redistribution? Choose one: by inactivating both a flippase and a scramblase in the plasma membrane by inverting the existing plasma membrane by inactivating a scramblase in the plasma membrane by activating a scramblase and inactivating a flippase in the plasma membrane by boosting the activity of a flippase in the plasma membrane

by activating a scramblase and inactivating a flippase in the plasma membrane

You are packing for a hiking trip during which you'll be burning a lot of calories with physical activity. You want to pack as efficiently as possible since you need to carry a tent and all your food. You can get the most calories out of 5kg of food if it is in the form of: glycogen glucose fat starch

fat

After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule? Choose one: glucose glycogen fatty acids pyruvate amino acids

fatty acids

Under anaerobic conditions, which metabolic pathway regenerates the supply of NAD+ needed for glycolysis? Choose one: citric acid cycle breakdown of amino acids breakdown of fats fermentation formation of acetyl CoA

fermentation

When food is plentiful, animals can store glucose as what? Choose one: glycogen or starch acetyl CoA glycogen glucose 6-phosphate starch

glycogen