Bio 222 exam 2
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.
The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes.
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.
The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.
Tetrodotoxin is a potent toxin found in a variety of organisms including the pufferfish. The toxin binds to the extracellular side of the Na+ channel and prevents channel opening. This leads to paralysis of muscles, including the diaphragm. Death from respiratory failure can occur after ingestion of as little as 1 mg of the toxin. Why does this toxin cause paralysis? Choose one: A. The Na+ channel does not open wide enough to allow enough Na+ through the channel. B. The membrane depolarization is not amplified along the axon. C. The axon membranes become over-depolarized. D. The Na+ channels remain in the inactive, refractory state.
The membrane depolarization is not amplified along the axon.
In the final stage of the oxidation of food molecules, a gradient of protons is formed across the inner mitochondrial membrane, which is normally impermeable to protons. If cells were exposed to an agent that causes the membrane to become freely permeable to protons, which of the following effects would you expect to observe? (a) The ratio of ATP to ADP in the cytoplasm would fall. (b) NADH would build up. (c) Carbon dioxide production would cease. (d) The consumption of oxygen would fall.
The ratio of ATP to ADP in the cytoplasm would fall.
What is true of the organelles that produce ATP in eukaryotic animal cells? Choose one: A. They have a separate set of DNA that contains many of the same genes found in the nucleus. B. They harbor eukaryotic-like biosynthetic machinery for making RNA and protein. C. They contain the same genes as the chloroplasts of plant cells. D. They reproduce sexually. E. They evolved from bacteria engulfed by ancestral cells billions of years ago.
They evolved from bacteria engulfed by ancestral cells billions of years ago.
In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. The energy of the thioester bond is harnessed in step 5. What is the energy used for? (a) to generate a molecule of GTP (b) to generate a molecule of ATP (c) to generate a proton gradient (d) to generate a molecule of NADH
To generate a molecule of GTP
Which two-carbon molecule enters the citric acid cycle? Choose one: pyruvate oxaloacetate citrate acetyl CoA carbon dioxide
acetyl CoA
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
active transport
Which of the following cells rely exclusively on glycolysis to supply them with ATP? (a) anaerobically growing yeast (b) aerobic bacteria (c) skeletal muscle cells (d) plant cells
anaerobically growing yeast
The link between bond-forming reactions and membrane transport processes in the mitochondria is called __________________. (a) chemiosmotic coupling (b) proton pumping (c) electron transfer (d) ATP synthesis
chemiosmotic coupling
Which component of the electron-transport chain is required to combine the pair of electrons with molecular oxygen? (a) cytochrome c (b) cytochrome b-c1 complex (c) ubiquinone (d) cytochrome c oxidase
cytochrome c oxidase
Which of the following processes generates the largest number of ATP molecules? Choose one: gluconeogenesis citric acid cycle electron transport chain fermentation glycolysis
electron transport chain
The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that ________________. (a) more free energy is released for a given amount of glucose oxidized (b) no energy is lost as heat (c) energy can be extracted in usable amounts (d) more CO2 is produced for a given amount of glucose oxidized
energy can be extracted in usable amounts
On a diet consisting of nothing but protein, which of the following is the most likely outcome? (a) loss of weight because amino acids cannot be used for the synthesis of fat (b) muscle gain because the amino acids will go directly into building muscle (c) tiredness because amino acids cannot be used to generate energy (d) excretion of more nitrogenous (ammonia-derived) wastes than with a more balanced diet
excretion of more nitrogenous (ammonia-derived) wastes than with a more balanced diet
Under anaerobic conditions, which metabolic pathway regenerates the supply of NAD+ needed for glycolysis? Choose one: fermentation breakdown of fats formation of acetyl CoA citric acid cycle breakdown of amino acids
fermentation
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
glucose
Which of the following polymer of glucose is used as a vehicle to store energy reserves in animal cells? (a) glucagon (b) glycogen (c) starch (d) glycerol
glycogen
Which of the following processes do not take place in the mitochondria? (a) citric acid cycle (b) conversion of pyruvate to activated acetyl groups (c) oxidation of fatty acids to acetyl CoA (d) glycogen breakdown
glycogen breakdown
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
inability to import sugar into the cell
In humans, glycogen is a more useful food storage molecule than fat because _____________________. (a) a gram of glycogen produces more energy than a gram of fat (b) it can be utilized to produce ATP under anaerobic conditions, whereas fat cannot (c) it binds water and is therefore useful in keeping the body hydrated (d) for the same amount of energy storage, glycogen occupies less space in a cell than does fat
it can be utilized to produce ATP under anaerobic conditions, whereas fat cannot
In anaerobic conditions, skeletal muscle produces _____________. (a) lactate and CO2 (b) ethanol and CO2 (c) lactate only (d) ethanol only
lactate only
Bongkrekic acid is an antibiotic that inhibits the ATP/ADP transport protein in the inner mitochondrial membrane. Which of the following will allow electron transport to occur in mitochondria treated with bongkrekic acid? (a) placing the mitochondria in anaerobic conditions (b) adding FADH2 (c) making the inner membrane permeable to protons (d) inhibiting the ATP synthase
making the inner membrane permeable to protons
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
Two molecules of CO2 are produced after the completion of a single citric acid reaction cycle. Where does the required oxygen come from? (a) water (b) phosphates (c) molecular oxygen (d) acetyl CoA
molecular oxygen
Glycolysis is an anaerobic process used to catabolize glucose. What does it mean for this process to be anaerobic? (a) No oxygen is required. (b) No oxidation occurs. (c) It takes place in the lysosome. (d) Glucose is broken down by the addition of electrons.
no oxygen is required
The reaction cycle that uses acetyl CoA to generate electron carrier molecules needed in the electron-transport chain is important for powering the cell. Which of the names below is not one of those commonly used to describe this reaction cycle? (a) tricarboxylic acid cycle (b) Krebs cycle (c) oxaloacetic acid cycle (d) citric acid cycle
oxaloacetic acid cycle
Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? (a) the digestion of starch to glucose (b) glycolysis (c) the citric acid cycle (d) oxidative phosphorylation
oxidative phosphorylation
The ethanol in wine and beer is produced from metabolic reactions carried out by the yeast Saccharomyces cerevisiae. Since it is of great commercial value, researchers have studied factors that influence ethanol production. To maximize ethanol yield, which environmental factor should be limiting? Choose one: A. oxygen B. sunlight C. glucose D. carbon dioxide
oxygen
A molecule moves down its concentration gradient by __________________ transport, but requires __________________ transport to move up its concentration gradient
passive and active
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. opening of ligand-gated ion channels B. active transport C. passive spread D. action potential E. opening of voltage-gated ion channels
passive spread
When protons move down their electrochemical gradient into the mitochondrial matrix, what do they do? Choose one: A. consume ATP B. produce ATP C. produce NADH D. move electrons through the respiratory chain D. produce NAD+
produce ATP
The movement of electrons through the electron-transport chain in mitochondria does which of the following? Choose one: A. pumps protons out of the mitochondrial matrix B. produces oxygen C. produces NADH D. pumps ATP across the inner mitochondrial membrane E. consumes ATP
pumps protons out of the mitochondrial matrix
The final metabolite produced by glycolysis is ___________. (a) acetyl CoA (b) pyruvate (c) 3-phosphoglycerate (d) glyceraldehyde 3-phosphate
pyruvate
Which of the following is not an electron carrier that participates in the electron-transport chain? (a) cytochrome (b) quinone (c) rhodopsin (d) copper ion
rhodopsin
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
specific binding to solutes
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
stress-gated
What is the name of the specialized junction between a neuron and a target cell?Choose one: A. synaptic vesicle B. axon C. dendrite D. nerve terminal E. synapse
synapse
The NADH generated during glycolysis and the citric acid cycle feeds its high-energy electrons to which of the following? Choose one: H2O the electron transport chain the citric acid cycle FAD ADP
the electron transport chain
In the reaction cycle involved in the oxidation of pyruvate, what are the advantages of having three enzyme activities contained in a single large complex instead of having three smaller and physically independent enzymes?
the proximity of one enzyme to another increases the overall reaction rate this allows for coordinated control of enzyme activity this allows for channeling of intermediates, minimized side reactions
Glycolysis generates more stored energy than it expends. What is the net number of activated carrier molecules produced in this process (number and type of molecules produced minus the number of those molecules used as input)? (a) 6 ATP, 2 NADH (b) 4 ATP, 4 NADH (c) 2 ATP, 2 NADH (d) 4 ATP, 2 NADH
2 ATP and 2 NADH
Which of the following characteristics of K+ channels are important for the selectivity for K+ rather than other ions? Choose one or more: A. Carbonyl groups line the wall of the pore. B. Basic side chains line the wall of the pore. C. Acidic side chains line the wall of the pore. D. Four rigid protein loops line the narrowest part of the pore.
A and D
What occurs in the first step of the citric acid cycle? Choose one: A. Two molecules of acetyl CoA combine to form oxaloacetate. B. two-carbon molecule is combined with a four-carbon molecule to form citrate. C. CO2 is released. D. ATP is consumed. E. NADH is produced.
A two-carbon molecule is combined with a four-carbon molecule to form citrate.
Which activated carriers are produced by the citric acid cycle? Choose one or more: A. NADH B. NADPH C. FADH2 D. ATP E. GTP F. CO2
A, C, and E
Step 3 in glycolysis requires the activity of phosphofructokinase to convert fructose 6-phosphate into fructose 1,6-bisphosphate. Which of the following molecules is an allosteric inhibitor of this enzyme? (a) Pi (b) AMP (c) ADP (d) ATP
ATP
The conversion of fructose 1,6-bisphosphate is catalyzed by a fructose 1,6-bisphosphatase and is one of the final steps in gluconeogenesis. Which of the following molecules is an allosteric activator of this enzyme? (a) Pi (b) AMP (c) ADP (d) ATP
ATP
Which activated carrier contains a high-energy bond whose hydrolysis releases a large amount of free energy? Choose one: A. ATP B. water C. NADH D. high-energy electrons E. glucose
ATP
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.
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.
Which of these processes require a membrane? Choose one or more: A. generation of ATP by glycolysis B. generation of energy by mitochondria C. generation of ATP by photosynthesis in plants D. generation of ATP by photosynthesis in bacteria E. generation of ATP by oxidative phosphorylation
B, C, D, and E
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
Benzene,
Fatty acids can easily be used to generate energy for the cell. Which of the following fatty acids will yield more energy? Explain your answer. (a) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH=CH-COOH (b) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH (c) CH3-CH=CH-CH2-CH2-CH2-CH2-CH=CH-COOH (d) CH3-CH2-CH2-CH2-CH2-CH2-CH2-COOH
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH
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. Carbonyl groups lining the wall of the pore can interact with the unsolvated K+ ion, balancing the energy needed to remove the hydration shell. 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. 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. D. The K+ channel uses the energy in ATP hydrolysis to remove the hydration shell from the K+ ion.
Carbonyl groups lining the wall of the pore can interact with the unsolvated K+ ion, balancing the energy needed to remove the hydration shell.
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-
Cl
In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. What molecule provides the sulfhydryl group necessary to form the thioester bond? (a) pyruvate (b) acetyl CoA (c) CoA (d) cysteine side chain in the catalytic pocket
CoA
What catabolic process uses substrate-level phosphorylation, and how many ATP molecules are generated in this way in the reaction pathway?
Glycolysis uses substrate-level phosphorylation and generates two ATP molecules for each glucose molecule oxidized to pyruvate molecules (four total ATPs, but two of these are hydrolyzed in the first several steps).
During electron transport, which serves as a ready source for protons that can be pumped across the membrane? Choose one: A. NADH B. O2 C. H2O D. glucose E. ATP
H2O
In the electron transport chain, the oxygen atoms in O2 become part of which of the following molecules? Choose one: glucose (C6H12O6) H2O NADH ATP CO2
H2O
How does the generation of ATP by oxidative phosphorylation differ from ATP generation by substrate-level phosphorylation?
In oxidative phosphorylation, molecular oxygen is required to produce ATP, by means of multistage, chemiosmotic process (see Chapter 14), while in substrate- level phosphorylation the energy released by the enzyme-catalyzed oxidation of a substrate generates ATP directly.
Some bacteria can live both aerobically and anaerobically. How does the ATP synthase in the plasma membrane of the bacterium help such bacteria to keep functioning in the absence of oxygen?
In the absence of oxygen, the respiratory chain no longer pumps protons, and thus no proton electrochemical gradient is generated across the bacterial membrane. In these conditions, the ATP synthase uses some of the ATP generated by glycolysis in the cytosol to pump protons out of the bacterium, thus forming the proton gradient across the membrane that the bacterium requires for importing vital nutrients by coupled transport.
For voltage-gated channels, a change in the membrane potential has what effect on the channel? Choose one: A. It makes the channel more sensitive to the binding of neurotransmitters. B. It changes which ions can pass through the channel. C. It changes the width of the channel opening. D. It alters the probability that the channel will be found in its open conformation.E. It either opens the channel or closes it, depending on the voltage.
It alters the probability that the channel will be found in its open conformation.E. It either opens the channel or closes it, depending on the voltage.
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.
It becomes more positive
What purpose does the phosphorylation of glucose to glucose 6-phosphate by the enzyme hexokinase serve as the first step in glycolysis? (a) It helps drive the uptake of glucose from outside the cell. (b) It generates a high-energy phosphate bond. (c) It converts ATP to a more useful form. (d) It enables the glucose 6-phosphate to be recognized by phosphofructokinase, the next enzyme in the glycolytic pathway.
It helps drive the uptake of glucose from outside the cell.
Which is not true about the acetylcholine receptor on vertebrate muscle cells? Choose one: A. It does not discriminate between Na+, K+, and Ca2+. B. Even with acetylcholine bound, it flickers randomly between open and closed states. C. It depolarizes the muscle cell membrane when bound to acetylcholine. D. It is a voltage-gated cation channel.E. Its pore includes negatively charged amino acid side chains at both ends.
It is a voltage-gated cation channel.E. Its pore includes negatively charged amino acid side chains at both ends.
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.
It opens more frequently in response to a given stimulus.
in most animal cells, which ion can move through "leak" channels?Choose one: H+ Cl- Ca2+ Na+ K+
K+
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
K+-coupled
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: NADH NAD+ ADP FADH2 ATP
NAD+
NADH contains a high-energy bond that, when cleaved, donates a pair of electrons to the electron-transport chain. What are the immediate products of this bond cleavage? (a) NAD+ + OH- (b) NAD+ + H- (c) NAD- + H+ (d) NAD + H
NAD+ + H-
In the final step of the citric acid cycle, oxaloacetate is regenerated through the oxidation of malate and coupled with the production of what other molecule? (a) FADH (b) NADH (c) GTP (d) CO2
NADH
Pyruvate can be converted into many other molecules by various biosynthetic and metabolic pathways, which makes it a central hub in the regulation of cellular metabolism. Which of the following molecules is not made from pyruvate? (a) oxaloacetate (b) ethanol (c) lactate (d) NADH
NADH
Most of the energy for the synthesis of ATP comes from which molecule? Choose one: A. FADH2 produced by the citric acid cycle B. NADH produced by the citric acid cycle C. NADH produced by the conversion of pyruvate to acetyl CoA D. GTP produced by the citric acid cycle E. NADH produced by glycolysis
NADH produced by the citric acid cycle
In eukaryotic cells, what is the final electron acceptor in the electron transport chain? Choose one: ATP NAD+ FADH2 CO2 O2
O2
In oxidative phosphorylation, ATP production is coupled to the events in the electron-transport chain. What is accomplished in the final electron transfer event in the electron-transport chain? (a) OH- is oxidized to O2. (b) Pyruvate is oxidized to CO2. (c) O2 is reduced to H2O. (d) NAD+ is reduced to NADH.
O2 is reduced to H2O
Where does oxidative phosphorylation take place, and what other processes are required for this to occur?
Oxidative phosphorylation takes place in mitochondria as part of multi-stage oxidation process. First the citric acide cycle generates NADH and FADH2, which donate their high-energy electrons to the electron-transport chain. These electrons ultimately reduce molecular oxygen to water, and the energy of their oxidation is used to pump protons across a membrane. The proton gradient thereby produced is in turn harnessed by the enzyme ATP synthase to drive the production of ATP from ADP and inorganic phosphate.
In which of the four compartments of a mitochondrion are each of the following located? A. porin B. the mitochondrial genome C. citric acid cycle enzymes D. proteins of the electron-transport chain E. ATP synthase F. membrane transport protein for pyruvate
Porin
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.
Some channels remain closed and some open completely.