Questions and Answers of Biochemistry Concepts And Connections

Would eating candy bars, high in sucrose rather than complex carbohydrates, help build up glycogen stores?
Would it be advantageous to consume a candy bar with a high refined-sugar content immediately before you start the strenuous hike in Question 9?Question 9You are planning to go on a strenuous hike
The concentration of lactate in blood rises sharply during a sprint and declines slowly for about an hour afterward.What causes the rapid rise in lactate concentration? What causes the decline in
A researcher claims to have discovered a variant form of glycogen. The variation is that it has very few branches (every 50 glucose residues or so) and that the branches are only three residues long.
What is the source of the energy needed to incorporate glucose residues into glycogen? How is it used?
Why is it useful to have a primer in glycogen synthesis?
Is the glycogen synthase reaction exergonic or endergonic? What is the reason for your answer?
Briefly describe “going for the burn” in a workout in terms of the material in this chapter.
Suggest a reason why sugar nucleotides, such as UDPG, play a role in glycogen synthesis, rather than sugar phosphates, such as glucose-6-phosphate.
What reactions in this chapter require acetyl-CoA or biotin?
What is the role of biotin in gluconeogenesis?
How does the role of glucose-6-phosphate in gluconeogenesis differ from that in glycolysis?
Avidin, a protein found in egg whites, binds to biotin so strongly that it inhibits enzymes that require biotin.What is the effect of avidin on glycogen formation? On gluconeogenesis?On the pentose
How does the hydrolysis of fructose-1,6-bisphosphate bring about the reversal of one of the physiologically irreversible steps of glycolysis?
How does fructose-2,6-bisphosphate play a role as an allosteric effector?
What is the Cori cycle?
Earlier biochemists called substrate cycles “futile cycles.” Why might they have chosen such a name? Why is it something of a misnomer?
How can different time scales for response be achieved in control mechanisms?
Why would you expect to see that reactions of substrate cycles involve different enzymes for different directions?
Suggest a reason or reasons why the Cori cycle takes place in the liver and in muscle.
How is it advantageous for animals to convert ingested starch to glucose and then to incorporate the glucose into glycogen?
How does control of the glucose-6-phosphatase reaction differ from that of the fructose-1,6-bisphosphatase reaction?
How does the action of allosteric effectors differ in the reactions catalyzed by phosphofructokinase and fructose-1,6-bisphosphatase?
Name two forms of control of enzymatic action. Which of the two is more important in control of glycogen breakdown?
What role does insulin play in glycogen synthesis?
What roles do glucagon and epinephrine play in glycogen breakdown?
How do glucagon and epinephrine differ in chemical structure?
What are four possible metabolic fates of glucose-6-phosphate?
Show how the pentose phosphate pathway, which is connected to the glycolytic pathway, can do the following.(a) Make both NADPH and pentose phosphates, in roughly equal amounts(b) Make mostly or
What is a major difference between transketolase and transaldolase?
Using the Lewis electron-dot notation, show explicitly the transfer of electrons in the following redox reactionThe lactone is a cyclic ester that is an intermediate in the production of
Does thiamine pyrophosphate play a role in the reactions of the pentose phosphate pathway? If so, what is that role?
Suggest a reason why a different reducing agent (NADPH) is used in anabolic reactions rather than NADH, which plays a role in catabolic ones.
Why is it reasonable to expect that glucose- 6-phosphate will be oxidized to a lactone rather than to an open-chain compound?
Which pathways are involved in the anaerobic metabolism of glucose? Which pathways are involved in the aerobic metabolism of glucose?
How many ATPs can be produced from one molecule of glucose anaerobically? Aerobically?
What are the different names used to describe the pathway discussed in this chapter?
What is meant by the statement that a pathway is amphibolic?
In what part of the cell does the citric acid cycle take place?Does this differ from the part of the cell where glycolysis occurs?
How does pyruvate from glycolysis get to the pyruvate dehydrogenase complex?
What electron acceptors play a role in the citric acid cycle?
What three molecules produced during the citric acid cycle are an indirect or direct source of high-energy compounds?
Briefly describe the dual role of lipoic acid in the pyruvate dehydrogenase complex.
What is the advantage to the organization of the PDH complex?
In the PDH reaction alone, we can see cofactors that come from four different vitamins. What are they?
Prepare a sketch showing how the individual reactions of the three enzymes of the pyruvate dehydrogenase complex give rise to the overall reaction.
Why is the reaction catalyzed by citrate synthase considered a condensation reaction?
With respect to stereochemistry, what is unique about the reaction catalyzed by aconitase?
In which steps of the aerobic processing of pyruvate is CO2 produced?
In which steps of the aerobic processing of pyruvate are reduced electron carriers produced?
What type of reaction is catalyzed by isocitrate dehydrogenase and α-ketoglutarate dehydrogenase?
What does it mean when an enzyme is called a synthetase?
Give an example of substrate-level phosphorylation in a pathway other than the citric acid cycle.
Why can we say that production of a GTP is equivalent to production of an ATP?
ATP is a competitive inhibitor of NADH binding to malate dehydrogenase, as are ADP and AMP. Suggest a structural basis for this inhibition.
Is the conversion of fumarate to malate a redox (electron transfer) reaction? Give the reason for your answer.
Which steps of aerobic metabolism of pyruvate through the citric acid cycle are control points?
Describe the multiple ways that PDH is controlled.
What are the two most common inhibitors of steps of the citric acid cycle and the reaction catalyzed by pyruvate dehydrogenase?
Acetyl-CoA and succinyl-CoA are both high energy thioesters, but their chemical energy is put to different uses. Elaborate.
Some reactions of the citric acid cycle are endergonic. Show how the overall cycle is exergonic.
Which enzymes of the citric acid cycle are missing from the glyoxylate cycle?
What are the unique reactions of the glyoxylate cycle?
Why is it possible for bacteria to survive on acetic acid as a sole carbon source, but not human beings?
The intermediates of glycolysis are phosphorylated, but those of the citric acid cycle are not. Suggest a reason why.
Discuss oxidative decarboxylation, using a reaction from this chapter to illustrate your points.
Many soft drinks contain citric acid as a significant part of their flavor. Is this a good nutrient?
What are the anaplerotic reactions in mammals?
Why is the citric acid cycle considered part of aerobic metabolism, even though molecular oxygen does not appear in any reaction?
Using the information in Table 20.2, calculate ΔG°' for the following reaction: 2 Cyt aa, [oxidized; Fe (III)] + 2 Cyt b [reduced; Fe (II)] → 2 Cyt aas [reduced; Fe (II)] + 2 Cyt b [oxidized; Fe
Why is it reasonable to compare the electron transport process to a battery?
Calculate E°' for the following reaction: NADH + H+ + O₂ → NAD+ + H₂O
Calculate E°' for the following reaction: NADH + H+ + Pyruvate → NAD+ + Lactate
Calculate E°' for the following reaction: Succinate + O₂ → Fumarate + H₂O 2
What do cytochromes have in common with hemoglobin or myoglobin?
How do the cytochromes differ from hemoglobin and myoglobin in terms of chemical activity?
Which of the following does not play a role in respiratory complexes: cytochromes, flavoproteins, iron–sulfur proteins, or coenzyme Q?
Do any of the respiratory complexes play a role in the citric acid cycle? If so, what is that role?
Do all the respiratory complexes generate enough energy to phosphorylate ADP to ATP?
Cytochrome oxidase and succinate-CoQ oxidoreductase are isolated from mitochondria and are incubated in the presence of oxygen, along with cytochrome c, coenzyme Q, and succinate. What is the overall
What is the advantage of having mobile electron carriers in addition to large membrane-bound complexes of carriers?
What is the advantage of having a Q cycle in electron transport in spite of its complexity?
Why do the electron-transfer reactions of the cytochromes differ in standard reduction potential, even though all the reactions involve the same oxidation–reduction reaction of iron?
Is there a fundamental difference between the one- and two-electron reactions in the electron transport chain?
What is the underlying reason for the differences in spectroscopic properties among the cytochromes?
What would be some of the challenges involved in removing respiratory complexes from the inner mitochondrial membrane in order to study their properties?
Describe the role of the F1 portion of ATP synthase in oxidative phosphorylation.
Is mitochondrial ATP synthase an integral membrane protein?
In what sense is mitochondrial ATP synthase a motor protein?
What is the approximate P/O ratio that can be expected if intact mitochondria are incubated in the presence of oxygen, along with added succinate?
Briefly summarize the main arguments of the chemiosmotic coupling hypothesis.
Why does ATP production require an intact mitochondrial membrane?
Briefly describe the role of uncouplers in oxidative phosphorylation.
What role does the proton gradient play in chemiosmotic coupling?
Why was dinitrophenol once used as a diet drug?
Criticize the following statement: “The role of the proton gradient in chemiosmosis is to provide the energy to phosphorylate ADP.”
What is the experimental evidence that mitochondria can change conformation during respiration?
Is it possible to have proton pumping in the absence of electron transport?
The malate–aspartate shuttle yields about 2.5 moles of ATP for each mole of cytosolic NADH. Why does nature use the glycerol–phosphate shuttle, which yields only about 1.5 moles of ATP?
What is the difference in the requirement for a primer in RNA transcription compared to DNA replication?

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