Chapter 13: How Cells Obtain Energy from Food

(Q009) The conversion of glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate in step 6 of glycolysis generates a "high-energy" phosphoanhydride bond. Which of the following BEST describes what happens to that bond in step 7? - It is hydrolyzed to drive the formation of ATP. - It is hydrolyzed to drive the formation of NADH. - It is hydrolyzed to generate pyruvate. - It is oxidized to CO2.

- It is hydrolyzed to drive the formation of ATP.

(Q040) 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? - The ratio of ATP to ADP in the cytoplasm would fall. - NADH would build up. - Carbon dioxide production would cease. - The consumption of oxygen would fall.

- The ratio of ATP to ADP in the cytoplasm would fall.

(Q018) Which of the following cells rely exclusively on glycolysis to supply them with ATP? - anaerobically growing yeast - aerobic bacteria - skeletal muscle cells - plant cells

- anaerobically growing yeast

(Q048) In humans, glycogen is a more useful food-storage molecule than fat because - a gram of glycogen produces more energy than a gram of fat. - it can be utilized to produce ATP under anaerobic conditions, whereas fat cannot. - it binds water and is therefore useful in keeping the body hydrated. - 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.

(Q006) 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)? - 6 ATP, 2 NADH - 4 ATP, 4 NADH - 2 ATP, 2 NADH - 4 ATP, 2 NADH

2 ATP, 2 NADH

(Q025) Pyruvate must move from the cytosol into the mitochondria, where it is oxidized to form CO2 and acetyl CoA by the pyruvate dehydrogenase complex. How many different enzymes and what total number of polypeptides, respectively, are required to perform this oxidation process in the mitochondrion? - 1; 60 - 3; 3 - 3; 26 - 3; 60

3; 60

(Q029) The citric acid cycle is a series of oxidation reactions that removes carbon atoms from substrates in the form of CO2. Once a molecule of acetyl CoA enters the citric acid cycle, how many complete cycles are required for both of the carbon atoms in its acetyl group to be oxidized to CO2? - 1 - 2 - 3 - 4

4

(Q032) In step 3 of the citric acid cycle, the oxidation of isocitrate and the production of CO2 are coupled to the reduction of NAD+, generating NADH and an α-ketoglutarate molecule. In the isocitrate molecule shown in Figure 13-32, which carbon is lost as CO2 and which is converted to a carbonyl carbon? - 4 and 5 - 6 and 5 - 5 and 4 - 6 and 4

6 and 4

(Q043) 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? - Pi - AMP - ADP - ATP

ATP

(Q044) The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate 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? - Pi - AMP - ADP - ATP

ATP

(Q026) The citric acid cycle is a critical sequence of reactions for energy production, which take place in the matrix of the mitochondria. The reaction cycle requires materials from the cytosol to be converted into acetyl CoA, which represents the starting point of a new cycle. Which of the following statements about acetyl CoA is TRUE? - Amino acids can be converted into acetyl CoA. - Pyruvate is converted into acetyl CoA in the cytosol. - Triacylglycerol molecules are transported into the mitochondrial matrix and cleaved by lipases to produce acetyl CoA. - Oxaloacetate is converted directly into acetyl CoA to feed the citric acid cycle.

Amino acids can be converted into acetyl CoA.

(Q033) 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. Which molecule provides the sulfhydryl group necessary to form the thioester bond? - pyruvate - acetyl CoA - CoA - cysteine side chain in the catalytic pocket

CoA

(Q017) What purpose does the phosphorylation of glucose to glucose 6-phosphate by the enzyme hexokinase serve as the first step in glycolysis? - It helps drive the uptake of glucose from outside the cell. - It generates a high-energy phosphate bond. - It converts ATP to a more useful form. - 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.

(Q023) The simultaneous oxidation and phosphorylation of glyceraldehyde 3-phosphate forms a highly reactive covalent thioester bond between a cysteine side chain (reactive group -SH) on the enzyme (glyceraldehyde 3-phosphate dehydrogenase) and the oxidized intermediate (see the arrow in Figure 13-23A). If the enzyme had a serine (reactive group -OH) instead of a cysteine at this position, which could form only a much lower energy bond to the oxidized substrate (see the arrow in Figure 13-23B), how might this new enzyme act? - It would oxidize the substrate and phosphorylate it without releasing it. - It would oxidize the substrate but not release it. - It would phosphorylate the substrate on the 2 position instead of the 1 position. - It would behave just like the normal enzyme.

It would oxidize the substrate but not release it.

(Q021) Glyceraldehyde 3-phosphate dehydrogenase operates by stripping a hydride ion from its substrate. Which molecule is the recipient of the proton and two electrons during this transfer? - oxygen - acetyl CoA - NAD+ - FADH

NAD+

(Q036) In the final step of the citric acid cycle, oxaloacetate is regenerated through the oxidation of malate and this is coupled with the production of which other molecule? - FADH - NADH - GTP - CO2

NADH

(Q047) 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? - oxaloacetate - ethanol - lactate - NADH

NADH

Glycolysis is an anaerobic process used to catabolize glucose. What does it mean for this process to be anaerobic? - No oxygen is required. - No oxidation occurs. - It takes place in the lysosome. - Glucose is broken down by the addition of electrons.

No oxygen is required.

(Q010) Steps 7 and 10 of glycolysis result in substrate-level phosphorylation. Which of the following best describes this process? - ATP is being hydrolyzed to phosphorylate the substrate. - The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP. - Two successive phosphates are transferred, first to AMP, then to ADP, finally forming ATP. - The substrate is hydrolyzed using ATP as an energy source.

The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP.

(Q031) In step 2 of the citric acid cycle, the enzyme aconitase generates isocitrate from citrate. Which of the following statements about this reaction is TRUE? - There is a substantial free-energy difference between the reactants and products of this reaction. - The unbonded electrons from hydroxide ions provide energy for this reaction. - The aconitase enzyme functions as a mutase in this reaction. - The reaction sequence first generates one molecule of water and then consumes one molecule of water.

The reaction sequence first generates one molecule of water and then consumes one molecule of water.

(Q022) The first energy-generating steps in glycolysis begin when glyceraldehyde 3-phosphate undergoes an energetically favorable reaction in which it is simultaneously oxidized and phosphorylated by the enzyme glyceraldehyde 3-phosphate dehydrogenase to form 1,3-bisphosphoglycerate, with the accompanying conversion of NAD+ to NADH. In a second energetically favorable reaction catalyzed by a second enzyme, the 1,3-bisphosphoglycerate is then converted to 3-phosphoglycerate, with the accompanying conversion of ADP to ATP. Which of the following statements is TRUE about this reaction? - The reaction glyceraldehyde 3-phosphate → 1,3-bisphosphoglycerate should be inhibited when levels of NADH fall. - The ΔG° for the oxidation of the aldehyde group on glyceraldehyde 3-phosphate to form a carboxylic acid is more negative than the ΔG° for ATP hydrolysis. - The energy stored in the phosphate bond of glyceraldehyde 3-phosphate contributes to driving the reaction forward. - The cysteine side chain on the enzyme is oxidized by NAD+.

The ΔG° for the oxidation of the aldehyde group on glyceraldehyde 3-phosphate to form a carboxylic acid is more negative than the ΔG° for ATP hydrolysis.

(Q030) In step 1 of the citric acid cycle, citrate is generated by the enzyme citrate synthase. The enzyme combines the two-carbon acetyl group from acetyl CoA and the four-carbon oxaloacetate. What is the source of energy that drives this reaction forward? - a high-energy phosphodiester bond - a transfer of high-energy electrons - a high-energy thioester bond - the heat of molecular collision

a high-energy thioester bond

(Q008) In step 4 of glycolysis, a six-carbon sugar (fructose 1,6-bisphosphate) is cleaved to produce two three-carbon molecules (dihydroxyacetone phosphate and glyceraldehyde 3-phosphate). Which enzyme catalyzes this reaction? - aldolase - phosphoglucose isomerase - enolase - triose phosphate isomerase

aldolase

(Q012) Which of the following descriptions best matches the function of a mutase? - an enzyme that catalyzes the rearrangement of bonds within a single molecule - an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule - an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion - an enzyme that catalyzes the addition of phosphate groups to other molecules

an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule

(Q011) Which of the following descriptions best matches the function of a kinase? - an enzyme that catalyzes the rearrangement of bonds within a single molecule - an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule - an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion - an enzyme that catalyzes the addition of phosphate groups to other molecules

an enzyme that catalyzes the addition of phosphate groups to other molecules

(Q013) Which of the following descriptions best matches the function of a dehydrogenase? - an enzyme that catalyzes the rearrangement of bonds within a single molecule - an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule - an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion - an enzyme that catalyzes the addition of phosphate groups to other molecules

an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion

(Q050) Which of the following descriptions best matches the function of an isomerase? - an enzyme that catalyzes the rearrangement of bonds within a single molecule -an enzyme that removes a specific chemical group from a molecule - an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion - an enzyme that catalyzes the addition of phosphate groups to other molecules

an enzyme that catalyzes the rearrangement of bonds within a single molecule

(Q020) Select the best option to fill in the blanks of the following statement: Fermentation is a/an __________ process that converts __________into carbon dioxide and __________. - anaerobic, pyruvate, ethanol - anaerobic, lactate, ethanol - eukaryotic, glyceraldehyde 3-phosphate, ethanol - prokaryotic, lactate, propanol

anaerobic, pyruvate, ethanol

(Q024) In the absence of oxygen, yeast cells can switch to a completely anaerobic metabolism called fermentation. Which of the following is a final product of fermentation in yeast? - a - b - c - d

b

(Q028) 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

b. CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH

(Q041) Pyruvate is an important metabolic intermediate that can be converted into several other compounds, depending on which enzyme is catalyzing the reaction. Which of the following CANNOT be produced from pyruvate in a single enzyme-catalyzed reaction? - lactate - oxaloacetate - citrate - alanine

citrate

(Q007) Which of the following steps or processes in aerobic respiration include the production of carbon dioxide? - breakdown of glycogen - glycolysis - conversion of pyruvate to acetyl CoA - oxidative phosphorylation

conversion of pyruvate to acetyl CoA

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 - more free energy is released for a given amount of glucose oxidized. - no energy is lost as heat. - energy can be extracted in usable amounts. - more CO2 is produced for a given amount of glucose oxidized.

energy can be extracted in usable amounts.

(Q014) On a diet consisting of nothing but protein, which of the following is the most likely outcome? - loss of weight because amino acids cannot be used for the synthesis of fat - muscle gain because the amino acids will go directly into building muscle - tiredness because amino acids cannot be used to generate energy - 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

(Q046) The intermediates of the citric acid cycle are constantly being depleted because they are used to produce many of the amino acids needed to make proteins. The enzyme pyruvate carboxylase converts pyruvate to oxaloacetate to replenish these intermediates. Bacteria, but not animal cells, have additional enzymes that can carry out the reaction acetyl CoA + isocitrate → oxaloacetate + succinate. Which of the following compounds will NOT support the growth of animal cells when used as the major source of carbon in food, but will support the growth of nonphotosynthetic bacteria? - pyruvate - glucose - fatty acids - fructose

fatty acids

(Q035) Step 6 of the citric acid cycle is catalyzed by succinate dehydrogenase. Keeping in mind that dehydrogenases catalyze redox reactions, which are the products of the reaction in which succinate is oxidized? - fumarate, NADH - fumarate, FADH2 - fumarate, FADH2 - succinyl CoA, NADH

fumarate, FADH2

(Q016) Which reaction does the enzyme phosphoglucose isomerase catalyze? - glucose → glucose 6-phosphate - fructose 6-phosphate → fructose 1,6-bisphosphate - glucose 6-phosphate → fructose 6-phosphate - glucose → glucose 1-phosphate

glucose 6-phosphate → fructose 6-phosphate

(Q045) Which of the following polymers of glucose is used as a vehicle to store energy reserves in animal cells? - glucagon - glycogen - starch - glycerol

glycogen

(Q015) Which of the following processes do NOT take place in the mitochondria? - citric acid cycle - conversion of pyruvate to activated acetyl groups - oxidation of fatty acids to acetyl CoA - glycogen breakdown

glycogen breakdown

(Q049) The concentration of H+ ions inside the mitochondrial matrix is lower than it is in the cytosol or the mitochondrial intermembrane space. What would be the IMMEDIATE effect of a membrane-permeable compound that carries and releases protons into the mitochondrial matrix? - inhibition of the electron-transport chain - inhibition of ATP synthesis - increased import of ADP into the matrix - inhibition of the citric acid cycle

inhibition of ATP synthesis

(Q019) In anaerobic conditions, skeletal muscle produces - lactate and CO2. - ethanol and CO2. - lactate only - ethanol only.

lactate only.

(Q042) When glucose is being used up and not replaced from food intake, the blood sugar level can be maintained by synthesizing glucose from smaller molecules such as pyruvate or lactate. This process is called gluconeogenesis. Which organ is principally responsible for supplying glucose to the rest of the body when glucose reserves are low? - liver - pancreas - spleen - gall bladder

liver

(Q037) The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. What compound served as the inhibitor? - malonate - malate - fumarate - succinate

malonate

Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? - the digestion of starch to glucose - glycolysis - the citric acid cycle - oxidative phosphorylation

oxidative phosphorylation

(Q005) The final metabolite produced by glycolysis is - acetyl CoA. - pyruvate - 3-phosphoglycerate. - glyceraldehyde 3-phosphate.

pyruvate

(Q004) Foods are broken down into simple molecular subunits for distribution and use throughout the body. Which type of simple subunits, listed below, is used preferentially as an energy source? - simple sugars - proteins - free fatty acids - glycerol

simple sugars

(Q039) The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. Which product in the reaction pathway builds up when the inhibitor is added? - citrate - succinate - fumarate - malate

succinate

(Q038) The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. Which enzyme was inhibited? - aconitase - isocitrate dehydrogenase - malate dehydrogenase - succinate dehydrogenase

succinate dehydrogenase

(Q034) 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? - to generate a molecule of GTP - to generate a molecule of ATP - to generate a proton gradient - to generate a molecule of NADH

to generate a molecule of GTP

(Q027) The citric acid cycle is a series of oxidation reactions that removes carbon atoms from substrates in the form of CO2. Where do the oxygen atoms in the carbon dioxide molecules come from? - water - phosphates - molecular oxygen - acetyl CoA

water