Chapter 19 QUESTIONS

• Which of the following enzymesdoes not use NAD+ for oxidation?

A. Alpha-Ketoglutarate Dehydrogenase complex.

• Which of these enzymes is most similar to pyruvate dehydrogenase?

A. Alpha-Ketoglutarate Dehydrogenase complex.

• Which of the following is true regarding the control of pyruvate dehydrogenase?

A. It is inhibited by ATP

• When acetyl-CoA reacts with oxaloacetate to form citrate

A. a new carbon-carbon bond is formed

• The reactions in which succinate is converted to oxaloacetate are, in order

A. an oxidation, a dehydration, and an oxidation

• The intracellular site of the glyoxylate cycle is

A. glyoxysomes only.

• Which of the following enzymes is allosterically activated by NAD+?

A. isocitrate dehydrogenase

• Which enzymes in the citric acid cycle catalyze oxidative decarboxylation reactions?

A. isocitrate dehydrogenase and the a-ketoglutarate dehydrogenase complex

The citric acid cycle is amphibolic, meaning

A. it plays a role in both anabolism and catabolism.

• Which of the following enzymes is allosterically inhibited by ATP?

A. pyruvate dehydrogenase complex

• The citric acid cycle is considered part of aerobic metabolism even though oxygen does not appear explicitly in any reaction because

A. the NADH and FADH2 produced are reoxidized in the electron transport chain linked to oxygen

• A control point outside the citric acid cycle is the reaction catalyzed by

A. the pyruvate dehydrogenase complex.

• The order of compounds and intermediates found in the citric acid cycle is as follows:

Aconitate ® IsoCitrate ® a-Ketoglutarate ®Fumarate ® Malate ® Oxaloacetate

Which of the following statements concerning the citric acid cycle as the central metabolic pathway is true?

All of these

• Thiamine pyrophosphate carries a ____ carbon unit.

B. 2

• The immediate electron acceptor for the majority of the oxidative reactions of the citric acid cycle is

B. NAD.

• There is a cyclic reaction in which pyruvate becomes oxaloacetate. The oxaloacetate is converted to malate and then back to pyruvate.

B. NADH is converted to NADPH in this cycle.

• Which of the following is not a reaction occurring during oxidative decarboxylation of pyruvate?

B. Oxidation of an acetate group.

• Release of succinate from succinyl-CoA can be coupled to GTP synthesis because:

B. The thioester bond between succinate and CoA has a large -DG of hydrolysis.

• The conversion of citrate to isocitrate is remarkable because

B. a chiral center is introduced in a molecule that did not have one previously.

• The acetyl group is carried on lipoic acid as

B. a thioester.

• A unique feature of the glyoxylate cycle is that it allows the organisms that possess this pathway to

B. produce carbohydrates from fats.

• In which cellular location do the majority of the reactions of the citric acid cycle take place?

B. the mitochondrial matrix.

• An organism that undergoes the glyoxylate cycle can make sugar from fat because:

B. the unique reactions of the glyoxylate cycle bypass the two decarboyxlation reactions of the citric acid cycle

• The anaplerotic reactions associated with the citric acid cycle are the result of

B. the use of many of the citric acid cycle intermediates in anabolism

• "Energy charge" in a cell is a measure of

C. ATP/ADP ratios.

• In the classical equation for respiration:Glucose + 6O2 --> 6CO2 + 6H2O, the following molecules are found directly in the citric acid cycle:

C. CO2 and H2O

• Which of the following statements concerning the glyoxylate pathway is False?

C. It does not occur in the mitochondria.

• Which of the following enzymes is the only membrane-bound enzyme in the citric acid cycle?

C. Succinate Dehydrogenase.

• In muscle cells, the following reaction proceeds as written, i.e.,from left to right, despite havingDG°' » +30 kJ/mol. How can this occur? malate + NAD+ ® oxaloacetate + NADH + H+

C. The concentration of malate must be higher than oxaloacetate for this reaction to occur in the cell.

• All but one of the enzymes of the citric acid cycle are found in this part of the mitochondrion:

C. The mitochondrial matrix.

• A cell in an active metabolic state has

C. a low (ATP/ADP) and a low (NADH/NAD+) ratio.

• Which of the following enzymesis not a control point of the citric acid cycle?

C. aconitase

• Which coenzyme listed below isnot associated with the a-ketoglutarate dehydrogenase complex?

C. biotin

• Which of the following is a source of NADPH?

C. both of the above

• The glyoxylate cycle occurs in

C. plants and bacteria.

• Which of the following enzymes contains a non-heme iron?

C. succinate dehydrogenase

• Which of the reactions of the citric acid cycle requires FAD as a coenzyme?

C. the conversion of succinate to fumarate

• The reaction in which malate is oxidized to oxaloacetate is not thermodynamically favored. It takes place because

C. the product is continuously used up in the next reaction of the cycle, which is thermodynamically favored.

• The conversion of malate to oxaloacetate has a high +DG (it is endergonic). It can take place because:

D. . The oxaloacetate product is used up in the subsequent reaction.

• Fluorine is related to the citric acid cycle because:

D. all of these

• Most of the products of the catabolism of sugars, fats and amino acids enter the citric acid cycle as:

D. all of these

• The enzymes involved in the pyruvate dehydrogenase complex are

D. associated with each other in a cubical array

• In the conversion of succinyl-CoA to succinate, GTP is produced from GDP in a reaction in which the source of the added phosphate is

D. inorganic phosphate ion.

• In the glyoxylate cycle, acetyl-CoA reacts with glyoxylate to produce

D. malate

• Which of the following cannot cross the inner mitochondrial membrane?

D. oxaloacetate

• The glyoxylate pathway bypasses part of the citric acid cycle by converting isocitrate to glyoxylate and

D. succinate

• The reaction of the citric acid cycle that does not take place in the mitochondrial matrix is the one catalyzed by:

D. succinate dehydrogenase

• Which of the following reactions involves substrate-level phosphorylation?

D. succinyl-CoA ® succinate

• Which of the following vitamins and enzyme cofactors are used by the pyruvate dehydrogenase complex during oxidative decarboxylation?

E. All of these

• Which of the following describes a use for acetyl-CoA as an important intermediate in metabolism?

E. All of these are reasons why acetyl-CoA is a central molecule in metabolism.

• Which of the following is not a component of the pyruvate dehydrogenase complex?

E. aconitase

• Intermediates of the citric acid cycle are especially important in the synthesis of fatty acids and amino acids. T/F

FALSE

• Lipoic acid is a required vitamin in the human diet. T/F

FALSE

• One round of the citric acid cycle generates about ten equivalents of ATP. T/F

FALSE

• The citric acid cycle uses anaplerotic reactions to get rid of the many intermediates of the cycle that accumulate during catabolism of amino acids. T/F

FALSE

• The enzyme "aconitase" is also known as "condensing enzyme" T/F

FALSE

• The iron ion, which is part of succinate Tdehydrogenase, is bonded to heme. T/F

FALSE

• The only difference between succinate and fumarate is the geometry around their double bonds, one contains a cis double bond and the other contains a trans double bond. T/F

FALSE

The citric acid cycle is the only metabolic pathway that can be used both as an anabolic and as a catabolic pathway. T/F

False

• Each of the enzymes of the pyruvate dehydrogenase complex requires a different vitamin. T/F

TRUE

• Glyoxysomes are named for the fact that they contain the glyoxylate pathway. T/F

TRUE

• The "energy charge" in a cell is important in the control of metabolism. T/F

TRUE

• The production of malate in the glyoxylate pathway is important, since it can be readily converted to phosphoenolpyruvate and then to sugars. T/F

TRUE

• Weight loss in humans can be difficult to achieve, since we lack the ability to convert our fats to sugars, and it is difficult to change our metabolism to using fats as a primary energy source. T/F

TRUE

• When the citric acid cycle is not functioning, the most common fate of acetyl-CoA from sugar metabolism in humans is the formation of fatty acids or cholesterol. T/F

TRUE