Chapter 13 How Cells Obtain Energy from Food
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.Figure (a) b.Figure (b) c.Figure (c) d.Figure (d)
Figure (b)
Do you expect the cell to produce more ATP from one glucose molecule or from one fatty acid molecule? Explain your answer.
More ATP is produced from fat catabolism than from glucose catabolism. Most ATP is generated in the mitochondria, and the amount depends on the production of the NADH and FADH2 cofactors in the Krebs cycle. The Krebs cycle relies on the input of acetyl CoA. Each glucose molecule can be converted into two acetyl CoA molecules. A molecule of fat will have three fatty acid chains, with an average length of 12-16 carbons. Even if we assume very short fatty acid chains of six carbons each (the length of a glucose molecule), this would mean the production of three acetyl CoA molecules per chain, and nine total for the triacylglycerol.
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? a.FADH b.NADH c.GTP d.CO2
NADH
Which reaction does the enzyme phosphoglucose isomerase catalyze? a. glucose → glucose 6-phosphate b. fructose 6-phosphate → fructose 1,6-bisphosphate c. glucose 6-phosphate → fructose 6-phosphate d. glucose → glucose 1-phosphate
glucose 6-phosphate → fructose 6-phosphate
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
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? a.liver b.pancreas c.spleen d.gall bladder
liver
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? a.malonate b.malate c.fumarate d.succinate
malonate
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 final metabolite produced by glycolysis is a.acetyl CoA. b.pyruvate. c.3-phosphoglycerate. d.glyceraldehyde 3-phosphate.
pyruvate
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? a.citrate b.succinate c.fumarate d.malate
succinate
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? a.aconitase b.isocitrate dehydrogenase c.malate dehydrogenase d.succinate dehydrogenase
succinate dehydrogenase
In anaerobic conditions, skeletal muscle produces a.lactate and CO2. b.ethanol and CO2. c.lactate only. d.ethanol only.
lactate only
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? a.1 b.2 c.3 d.4
4
Indicate whether the following statements are TRUE or FALSE. If a statement is false, explain why it is false. A.The proteins of the electron-transport chain remove a pair of high-energy electrons from the cofactors NADH and FADH2, after which the electrons move across the inner mitochondrial membrane to maintain the voltage gradient. B.Gluconeogenesis is a linear reaction pathway that the cell employs to generate glucose from pyruvate and is exactly the reverse of the reactions in the glycolytic pathway. C.With respect to the amount of energy stored in molecules of the body, 6 g of glycogen is the equivalent of 1 g of fat. D.Glycogen phosphorylase cleaves glucose monomers from the glycogen polymer, phosphorylating them at the same time so that they can be fed unchanged into the glycolytic pathway.
A.False. Although the proteins of the electron-transport chain collect electrons from the NADH and FADH2 cofactors, these high-energy electrons go through a series of transfers along the electron-transport chain. The energy released with each transfer moves protons across the inner mitochondrial membrane. It is this proton gradient that provides the energy to synthesize ATP. B.False. Gluconeogenesis can begin with pyruvate as a building block to make glucose, but there are three reactions in glycolysis that are irreversible because of a large free-energy barrier. Alternative enzymes and reaction pathways are used to bypass this problem, and they require the input of energy in the form of ATP and GTP. C.True. D.False. When glycogen phosphorylase cleaves a glucose monomer from glycogen, the product is glucose 1-phosphate. Before it can be used in glycolysis, it needs to be isomerized to glucose 6-phosphate.
Anaerobically growing yeast further metabolizes the pyruvate produced by glycolysis to CO2 and ethanol as part of a series of fermentation reactions. A.What other important reaction occurs during this fermentation step? B.Why is this reaction (that is, the answer to part A) essential for the anaerobically growing cell?
A.NADH → NAD+. B.Under anaerobic conditions, it is the only means of regenerating the NAD+ required for glycolysis, the main energy-generating pathway of an anaerobically growing yeast cell.
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 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? a.Pi b.AMP c.ADP d.ATP
ATP
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? a.Amino acids can be converted into acetyl CoA. b.Pyruvate is converted into acetyl CoA in the cytosol. c.Triacylglycerol molecules are transported into the mitochondrial matrix and cleaved by lipases to produce acetyl CoA. d.Oxaloacetate is converted directly into acetyl CoA to feed the citric acid cycle.
Amino acids can be converted into acetyl CoA.
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?
By co-localizing three enzyme activities in a large, layered complex, the substrates are already bound and properly positioned for rapid enzyme catalysis, and the free energy released by one reaction can be readily harnessed for the next.
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? a. It is hydrolyzed to drive the formation of ATP. b. It is hydrolyzed to drive the formation of NADH. c. It is hydrolyzed to generate pyruvate. d. It is oxidized to CO2.
It is hydrolyzed to drive the formation of ATP.
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? a.oxygen b.acetyl CoA c.NAD+ d.FADH
NAD+
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
Glycolysis and the citric acid cycle comprise two different sets of oxidation reactions. The reaction sequence for glycolysis is linear, whereas the reaction sequence for the citric acid cycle forms a circle. How does this difference in the arrangement of reactions influence the rate of these processes when an excess amount of a single intermediate is added?
Primarily, what is seen is that the citric acid cycle occurs more rapidly after the addition of any one of the intermediates. This means that if one intermediate is added, levels of all of them increase. In glycolysis, the intermediates downstream of the intermediate being added will be affected.
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.a high-energy phosphodiester bond b.a transfer of high-energy electrons c.a high-energy thioester bond d.the heat of molecular collision
a high-energy thioester bond
Which of the following descriptions best matches the function of an isomerase? a.an enzyme that catalyzes the rearrangement of bonds within a single molecule b.an enzyme that removes a specific chemical group from a molecule c.an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion d.an enzyme that catalyzes the addition of phosphate groups to other molecules
a. an enzyme that catalyzes the rearrangement of bonds within a single molecule b.an enzyme that removes a specific chemical group from a molecule
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? a. aldolase b. phosphoglucose isomerase c. enolase d. triose phosphate isomerase
aldolase
Which of the following descriptions best matches the function of a mutase? a. an enzyme that catalyzes the rearrangement of bonds within a single molecule b. an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule c. an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion d. 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
Which of the following descriptions best matches the function of a kinase? a. an enzyme that catalyzes the rearrangement of bonds within a single molecule b. an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule c. an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion d. an enzyme that catalyzes the addition of phosphate groups to other molecules
an enzyme that catalyzes the addition of phosphate groups to other molecules
Which of the following descriptions best matches the function of a dehydrogenase? a. an enzyme that catalyzes the rearrangement of bonds within a single molecule b. an enzyme that catalyzes a change in the position of a specific chemical group within a single molecule c. an enzyme that catalyzes the oxidation of a molecule by removing a hydride ion d. 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
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
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
Which of the following polymers of glucose is used as a vehicle to store energy reserves in animal cells? a.glucagon b.glycogen c.starch d.glycerol
glycogen
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? a.inhibition of the electron-transport chain b.inhibition of ATP synthesis c.increased import of ADP into the matrix d.inhibition of the citric acid cycle
inhibition of ATP synthesis
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, 2 NADH
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? a.1; 60 b.3; 3 c.3; 26 d.3; 60
3; 60
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? a.4 and 6 b.6 and 5 c.5 and 4 d.6 and 4
6 and 4
For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. amino acidsgalactosenucleotides carbon fixationglucoseoxidative phosphorylation citric acid cycleglycogen pyruvate fatty acidinsulinstarch fermentationlactatetriacylglycerol A carbon atom in a CO2 molecule in the atmosphere eventually becomes a part of one of the enzymes that catalyzes glycolysis in one of your cells. The CO2 first enters a cell in a corn leaf, where photosynthesis fixes the carbon to make it part of a sugar molecule; this travels from the leaf to an ear of corn, where it is stored as part of a polysaccharide __________ molecule in the corn seed. You then eat a corn chip made from the corn seed. You digest the corn seed, and the free __________ travels in your bloodstream, eventually being taken up by a liver cell and stored as __________. When required, this storage molecule breaks down into glucose 1-phosphate, which enters the glycolytic pathway. Glycolysis produces __________, which is converted into acetyl CoA, which enters the __________. Several intermediates in this process can provide the carbon skeleton for the production of __________, which are then incorporated into the enzymes that catalyze steps in glycolysis.
A carbon atom in a CO2 molecule in the atmosphere eventually becomes a part of one of the enzymes that catalyzes glycolysis in one of your cells. The CO2 first enters a cell in a corn leaf, where photosynthesis fixes the carbon to make it part of a sugar molecule; this travels from the leaf to an ear of corn, where it is stored as part of a polysaccharide starch molecule in the corn seed. You then eat a corn chip made from the corn seed. You digest the corn seed, and the free glucose travels in your bloodstream, eventually being taken up by a liver cell and stored as glycogen. When required, this storage molecule breaks down into glucose 1-phosphate, which enters the glycolytic pathway. Glycolysis produces pyruvate, which is converted into acetyl CoA, which enters the citric acid cycle. Several intermediates in this process can provide the carbon skeleton for the production of amino acids, which are then incorporated into the enzymes that catalyze steps in glycolysis.
Indicate whether the following statements are TRUE or FALSE. If a statement is false, explain why it is false. A.During glycolysis, glucose molecules are broken down to yield CO2 and H2O. B.The cleavage of fructose 1,6-bisphosphate yields two molecules of glyceraldehyde 3-phosphate. C.Anaerobic respiration is not the same as fermentation, as only the former requires an electron-transport chain. D.When subjected to anaerobic conditions, glycolysis in mammalian cells continues and causes a buildup of pyruvate in the cytosol. E.The pyruvate dehydrogenase complex catalyzes three different, but linked, enzymatic reactions. F.Amino acids can be transported into the mitochondria and converted into acetyl CoA.
A.False. At the end of a series of the 10 different reactions involved in glycolysis, the final products are two molecules of pyruvate. Pyruvate will later be broken down into CO2 and H2O in the citric acid cycle. B.False. When fructose 1,6-bisphosphate is cleaved, the products are dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Only after the subsequent isomerization of dihydroxyacetone phosphate is the second molecule of glyceraldehyde 3-phosphate produced. C.True. D.False. Under anaerobic conditions, mammalian cells convert pyruvate to lactate in a fermentation process. The lactate is subsequently excreted from the cell. E.True. F.True.
You are stranded on an island with no way to communicate or signal for help. Your only hope is that somebody has tracked your last known location and will begin a search from there. Nevertheless, it will be a while before you have a chance of seeing another person. You have found a fresh stream of water at the center of the island, but other than green leafy plants, food options appear nonexistent. A.What substances are used as energy stores within your body? In which organs? B.Which will be used first in the absence of ingesting external sources of energy? How long will this source last? C.What other substance will your body then turn to? On average, how long before you run out of that fuel source? Explain why this second fuel source is a better choice than the first-used source as your long-term energy store. D.What enzyme is required for the breakdown and usage of the energy source you listed in part B? If you are a person with a deficiency in that enzyme, how does this affect your other estimates?
A.Glycogen (a polymer of glucose, stored in the liver and skeletal muscle) and triacylglycerol (storage molecule for fatty acids in adipose) are the fuel molecules you have stored. The protein in your skeletal muscle can be broken down as the last fuel option your body has available. B.Glycogen in the liver will be the first fuel source consumed. This will be burned within the first 12-24 hours. Glycogen stored in your skeletal muscle tissue will be used as the liver glycogen levels go down, as your system attempts to maintain normal blood glucose levels. C.The triacylglycerol (TAG) molecules in adipose cells will be used as glycogen levels wane. These lipids are cleaved into glycerol and free fatty acids, and the fatty acids are released into the bloodstream for use by the rest of your body. TAG is a better storage molecule because fatty acid metabolism is more efficient (yields more ATP per molecule than glucose) and can be stored in a smaller volume. Glycogen is highly hydrated, and takes up more intracellular space than lipid droplets. Lipid stores could fuel your body as long as one month, depending on the net volume of lipids stored and your level of activity. D.Glycogen is broken in to glucose subunits by glycogen phosphorylase. A deficiency in this enzyme would mean that your ability to break down glycogen is impaired. In order to supplement the fuel to meet your body's needs, you may burn fatty acids more quickly. You should also expect your glycogen stores to last longer in both the liver and skeletal muscle.
Indicate whether the following statements are TRUE or FALSE. If a statement is false, explain why it is false. A.CO2 and H2O are generated during the oxidation of food molecules. B.Activated carrier molecules store heat energy for the cell to use later. C.Catabolism is a general term that refers to the processes by which large molecules are synthesized from smaller molecules. D.The oxidation of sugar is an energetically favorable process.
A.True. B.False. Activated carriers have high-energy bonds that can drive other reactions when broken. Heat may be released during these reactions and may increase the reaction rates, but is not a form of energy that is stored in biological systems. C.False. Catabolism comprises the metabolic reactions that are involved in breaking large molecules into smaller molecules. Anabolism encompasses the reverse types of reactions: synthesizing larger molecules from smaller molecules. D.True.
For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. Biological systems __________ hydrocarbons in stepwise __________ reactions. Glucose is the preferred energy source in eukaryotes, and must be converted into __________ before it can be transported across the __________ mitochondrial membrane for use in the citric acid cycle. The citric acid cycle is critical for the mitochondrion's subsequent production of __________. ATP catabolic inner outer permeable acetyl CoA electrons isomerize oxidize protons anabolic glycolysis kinase peptides pyruvate anaerobic GTP NADH
Biological systems oxidize hydrocarbons in stepwise catabolic reactions. Glucose is the preferred energy source in eukaryotes, and must be converted into pyruvate before it can be transported across the inner mitochondrial membrane for further oxidation in the citric acid cycle. The citric acid cycle is critical for the mitochondrion's subsequent production of ATP.
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
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? a.pyruvate b.acetyl CoA c.CoA d.cysteine side chain in the catalytic pocket
CoA
It can be useful to analyze the steps of glycolysis with respect to the four basic types of enzymes required by this central catabolic pathway and to consider whether each enzyme produces or harvests the energy of an activated carrier. For each step of glycolysis (see Figure 13-60 or Panel 13-1), indicate which type of enzyme (of the four listed below and in Table 13-60) is required—or if none apply. Also, indicate whether an activated energy carrier is involved, and, if so, how. Step 1__________ Step 2__________ Step 3__________ Step 4__________ Step 5__________ Step 6__________ Step 7__________ Step 8__________ Step 9__________ Step 10__________
Enzyme types: kinase, isomerase, mutase, dehydrogenase ANS: Step 1 kinase, energy in the form of ATP consumed Step 2 isomerase Step 3 kinase, energy in the form of ATP consumed Step 4 none of the above Step 5 isomerase Step 6 dehydrogenase, energy in the form of NADH produced Step 7 kinase (catalyzing its reverse reaction)*; energy in the form of ATP produced Step 8 mutase Step 9 none of the above Step 10 kinase (catalyzing its reverse reaction)*; energy in the form of ATP produced
Name the catabolic process that use substrate-level phosphorylation, identify where it takes place and how it is connected to oxidative phosphorylation.
Glycolysis employs substrate-level phosphorylation. The process occurs in the cytosol and generates a net total of two ATP molecules for each glucose molecule. The connection to oxidative phosphorylation is through the product of glycolysis: 2 pyruvate molecules for each glucose molecule. Pyruvate is shuttled into the mitochondria and converted into acetyl CoA. This acetyl CoA is oxidized in the citric acid cycle to generate the high-energy electrons in NADH and FADH2 that feed the electron-transport chain in the mitochondrial inner membrane that drives oxidative phosphorylation.
For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase may be used more than once. ADP FADH2 H+ moderately protons ATP favorable higher NADH severely cytosol glucose lower NAD+ slightly electrons GTP matrix Piun favorable High-energy electrons are transferred through a series of molecules, and the energy released during these transfers is used to generate a gradient of __________, or __________. Because their concentration is __________ outside than inside the mitochondria, the flow of __________, or __________, down the concentration gradient is energetically very __________ and can thus be coupled to the production of ATP from ADP. Thus, oxidative phosphorylation refers to the oxidation of __________ and __________ molecules and the phosphorylation of __________. Without this process, the yield of ATP from each glucose molecule would be __________ decreased.
High-energy electrons are transferred through a series of molecules, and the energy released during these transfers is used to generate a gradient of protons, or H+. Because their concentration is higher outside than inside the mitochondria, the flow of protons, or H+, down the concentration gradient is energetically very favorable and can thus be coupled to the production of ATP from ADP. Thus, oxidative phosphorylation refers to the oxidation of NADH and FADH2 molecules and the phosphorylation of ADP. Without this process, the yield of ATP from each glucose molecule would be severely decreased.
Provide a brief description of the process by which the body derives energy from food. Include in your description the three stages of catalysis, and delineate the input and output that connect each stage.
In the first stage of catabolism, polymers are broken down into smaller subunits in the digestive system, which stretches from the mouth to the gut. Proteins are converted to amino acids, fats to fatty acids and glycerol, and carbohydrates simple sugars, including the monosaccharide glucose. In the second stage of catabolism, these simple subunits are further broken down to generate the activated carrier acetyl CoA. Acetyl CoA is the molecular input for the third stage of metabolism. In the last stage of catabolism, the acetyl CoA is oxidized to CO2, coupled to the production of large amounts of ATP, which is used as chemical energy for the cell.
Although ATP and NADH are both important activated carrier molecules, ATP hydrolysis provides the direct molecular energy for most biochemical reactions. Why do the mitochondria also need to generate high levels of NADH?
NADH is an activated carrier molecule used as a cofactor for many enzymes that catalyze redox reactions. NADH also donates electrons to the electron-transport chain, which is essential for the production of ATP.
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.
Where does oxidative phosphorylation take place and what materials are the reactants and the products in this process?
Oxidative phosphorylation takes place in mitochondria as part of a multistage oxidation process. First, the citric acid 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 resulting proton gradient is harnessed by the enzyme ATP synthase to drive the production of ATP from ADP and Pi.
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.
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? a.There is a substantial free-energy difference between the reactants and products of this reaction. b.The unbonded electrons from hydroxide ions provide energy for this reaction. c.The aconitase enzyme functions as a mutase in this reaction. d.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.
Steps 7 and 10 of glycolysis result in substrate-level phosphorylation. Which of the following best describes this process? a. ATP is being hydrolyzed to phosphorylate the substrate. b. The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP. c. Two successive phosphates are transferred, first to AMP, then to ADP, finally forming ATP. d. The substrate is hydrolyzed using ATP as an energy source.
The substrate is hydrolyzed using ATP as an energy source.
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? a.The reaction glyceraldehyde 3-phosphate → 1,3-bisphosphoglycerate should be inhibited when levels of NADH fall. b.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. c.The energy stored in the phosphate bond of glyceraldehyde 3-phosphate contributes to driving the reaction forward. d.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.
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? a.lactate b.oxaloacetate c.citrate d.alanine
citrate
Which of the following steps or processes in aerobic respiration include the production of carbon dioxide? a. breakdown of glycogen b. glycolysis c. conversion of pyruvate to acetyl CoA d. 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 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
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? a.pyruvate b.glucose c.fatty acids d.fructose
fatty acids
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? a.fumarate, NADH b.fumarate, FADH2 c.fumarate, FADH2 d.succinyl CoA, NADH
fumarate, NADH
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 binds water and is therefore useful in keeping the body hydrated.
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? a.simple sugars b.proteins c.free fatty acids d.glycerol
simple sugars
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
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? a.water b.phosphates c.molecular oxygen d.acetyl CoA
water
Select the best option to fill in the blanks of the following statement: Fermentation is a/an __________ process that converts __________into carbon dioxide and __________. a.anaerobic, pyruvate, ethanol b.anaerobic, lactate, ethanol c.eukaryotic, glyceraldehyde 3-phosphate, ethanol d.prokaryotic, lactate, propanol
anaerobic, pyruvate, ethanol
