Deck 14: Carbohydrate Metabolism

Question 1

Which enzyme uses cellular NADPH to regenerate reduced glutathione?

A) glucose-6-phosphate dehydrogenase
B) glutathione peroxidase
C) glutathione reductase
D) hemoglobin

Answer 1

glutathione reductase

Question 2

Which enzyme in the pentose phosphate pathway catalyzes the following reaction?

A) glucose-6-phosphate dehydrogenase
B) transaldolase
C) 6-phosphogluconate dehydrogenase
D) ribulose-5-phosphate epimerase

Answer 2

6-phosphogluconate dehydrogenase

Question 3

Which of the following molecules is found in the nonoxidative phase of the pentose phosphate pathway?

A) glucose-6-phosphate
B) sedoheptulose-7-phosphate
C) phosphoenolpyruvate
D) CO₂

Answer 3

sedoheptulose-7-phosphate

Question 4

If the ratio of NADP⁺ to NADPH were high, the

A) net production of ATP would occur.
B) pentose phosphate pathway oxidative phase would be activated.
C) cellular levels of nucleotides would have to increase from an activated pentose phosphate pathway.
D) pentose phosphate pathway would be inhibited.

Question 5

What molecule activates the pentose phosphate pathway?

A) NADP⁺
B) ribulose-5-phosphate
C) ADP
D) NADH

Question 6

The pentose phosphate pathway occurs in the

A) cytoplasm.
B) nucleus.
C) Golgi apparatus.
D) mitochondria.

Question 7

The products of the oxidative portion of the pentose phosphate pathway are carbon dioxide and

A) 2 NADH + 1 hexose phosphate.
B) 2 NADP⁺ + 1 pentose phosphate.
C) 2 NADPH + 1 hexose phosphate.
D) 2 NADPH + 1 pentose phosphate.

Question 8

Starting from the oxidative phase of the pentose phosphate pathway, how many ATP and high-energy reduced molecules, respectively, are made in going from one glucose molecule to glyceraldehyde-3-phosphate and fructose-6-phosphate?

A) 0; 0
B) 0; 2
C) 2; 0
D) 2; 2

Question 9

Which of the following molecules is found in the nonoxidative phase of the pentose phosphate pathway?

A) ATP
B) NADPH
C) fructose-6-phosphate
D) CO₂

Question 10

Which of the following is NOT a role played by the pentose phosphate pathway?

A) converting pyruvate into TCA cycle intermediates
B) making NADPH for other metabolic pathways
C) converting 6C glucose into 5C ribose
D) converting DNA backbone sugars into glycolysis intermediates

Question 11

The pentose phosphate pathway

A) resembles the TCA cycle in that it couples the loss of CO₂ with the formation of NADH.
B) allows 5C sugars to converge with or diverge from the glycolysis pathway.
C) contains 2C, 3C, 4C, 5C, 6C, and 7C sugar molecules.
D) enables the production of ATP from glucose.

Question 12

Which of the following metabolites is NOT a gluconeogenesis substrate in humans?

A) pyruvate
B) lactate
C) oxaloacetate
D) acetate

Question 13

Which is the substrate or product of the reactions that comprise the oxidative branch of the pentose phosphate pathway?

A) sedoheptulose-7-phosphate
B) glyceraldehyde-3-phosphate
C) ribulose-5-phosphate
D) ribose-5-phosphate

Question 14

How would individuals with decreased levels of the pentose phosphate enzyme glucose-6-phosphate dehydrogenase respond to oxidative stress?

A) Higher than normal levels of NADPH would accumulate.
B) They would not have the ability to regenerate reduced glutathione as rapidly.
C) They would rapidly neutralize cellular levels of H₂O₂ and other reactive oxygen species.
D) They would compensate with higher than normal levels of pentose phosphate pathway activity.

Question 15

The main function of the pentose phosphate pathway is to provide

A) the cell with backup capability when glycolysis is inhibited.
B) energy and reducing power.
C) a mechanism for the utilization of the carbon skeletons of excess amino acids.
D) a source of ribose and NADPH.

Question 16

Which enzyme class catalyzes the following pentose phosphate pathway reaction?

A) lyase
B) transferase
C) oxidoreductase
D) isomerase

Question 17

The pentose phosphate pathway

A) can be used to make seduheptulose-7-phosphate for use in RNA and DNA synthesis.
B) is linked at its start and at its end to the glycolysis pathway.
C) converges glycolysis intermediates with TCA cycle intermediates.
D) occurs in the mitochondrial matrix of cells.

Question 18

What enzyme class in the nonoxidative phase of the pentose phosphate pathway allows for the reaction of ribose-5-phosphate and xylulose-5-phosphate to produce glyceraldehyde-3-phosphate and seduheptulose-7-phosphate?

A) isomerase
B) hydrolase
C) transferase
D) oxidoreductase

Question 19

Which enzyme class catalyzes the following pentose phosphate pathway reaction (note that there may be some missing reactants and products)?

A) lyase
B) isomerase
C) transferase
D) oxidoreductase

Question 20

Which enzyme in the pentose phosphate pathway is regulated to control flux through the pathway?

A) glucose-6-phosphate dehydrogenase
B) transaldolase
C) 6-phosphogluconate dehydrogenase
D) ribulose-5-phosphate epimerase

Question 21

In the reaction catalyzed by pyruvate carboxylase (the first reaction in gluconeogenesis), CO₂ is

A) lost from oxaloacetate.
B) activated by ATP energy.
C) activated by the cofactor NADH.
D) added to the phosphoenolpyruvate product.

Question 22

What molecules are missing from boxes in the gluconeogenesis reaction shown below?

A) Ser-P_i; Ser-P_i
B) H₂O; P_i
C) ADP; ATP
D) ATP; ADP

Question 23

Two moles of pyruvate molecules running through the gluconeogenesis pathway to give 1 mole of glucose requires the hydrolysis of moles of ATP equivalents.

A) 0
B) 2
C) 4
D) 6

Question 24

Which pathway is opposite to gluconeogenesis?

A) TCA cycle
B) glycogen synthesis pathway
C) pentose phosphate pathway
D) glycolysis pathway

Question 25

Which correctly describes the role of the transport system shown below?

A) It provides an alternate fate for pyruvate degradation.
B) It provides a source of NADH for gluconeogenesis via malate transport.
C) It converts NADH equivalents into reduced forms of carbon.
D) It allows for pyruvate transport into and out of the mitochondria.

Question 26

How many moles of NADH are required in gluconeogenesis to convert 2 moles of pyruvate molecules into 1 mole of glucose?

A) 0
B) 1
C) 2
D) 4

Question 27

The first two reactions of gluconeogenesis are required to reverse reaction 10 (or the last reaction) of glycolysis. How many ATP equivalents are used by these first two reactions of gluconeogenesis?

A) 1
B) 2
C) 3
D) 4

Question 28

In the gluconeogenesis pathway, the enzyme glucose-6-phosphatase reverses which step in glycolysis?

A) the formation of glucose
B) the reaction catalyzed by pyruvate dehydrogenase
C) the reaction catalyzed by hexokinase
D) the formation of fructose-1,6-bisphosphate

Question 29

Gluconeogenesis is favored when citrate levels are , when AMP levels are __________, and when ATP levels are _.

A) low; low; high
B) high; low; high
C) low; high; low
D) high; high; low

Question 30

Gluconeogenesis would most likely be allosterically activated simultaneously along with which other metabolic process?

A) glycolysis
B) pentose phosphate pathway
C) glycogen synthesis
D) TCA cycle

Question 31

Which of the following metabolites has carbon atoms that can end up in glucose via the gluconeogenesis pathway in humans?

A) CO₂
B) glycerol
C) ATP
D) NADH

Question 32

Cytoplasmic levels of NADH must be maintained in order for gluconeogenesis to occur. What generates NADH for this pathway?

A) the glycolysis pathway
B) the TCA cycle
C) the mitochondrial electron transport chain
D) the movement of NADH equivalents from inside the mitochondria via malate transport

Question 33

The regulated reactions of gluconeogenesis have/are

A) large positive $\Delta$ G values.
B) those that are counter to regulated reactions in glycolysis.
C) reversible reactions.
D) activated by molecules indicating a low energy charge in the cell.

Question 34

The hormone insulin activates phosphofructokinase 2 (2PFK2). This leads to a(n) __________ in concentration of fructose 2,6 bisphosphate, which favors the __________
Pathway.

A) increase; glycolysis
B) increase; gluconeogenesis
C) decrease; glycolysis
D) decrease; gluconeogenesis

Question 35

The gluconeogenesis pathway

A) converts NADH into NAD⁺ so that glycolysis can continue.
B) provides energy for the cell.
C) increases the ratio of ATP to ADP in the cell.
D) converts two 3C sugars into a 6C sugar.

Question 36

How many of the 10 glycolysis reactions use the same enzyme in the gluconeogenesis pathway?

A) 10
B) 7
C) 5
D) 3

Question 37

The conversion of pyruvate to phosphoenolpyruvate (PEP) in gluconeogenesis

A) requires the net input of two equivalents of NADH.
B) occurs in two steps and is catalyzed by the enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase.
C) is a thermodynamically spontaneous reaction that gives rise to a stable product.
D) requires lactate as a precursor.

Question 38

Of the four molecules listed below, three of them reciprocally regulate phosphofructokinase 1 (PFK1) and fructose-1,6-bisphosphatase. Which molecule does NOT fit?

A) pyruvate
B) fructose-2,6-bisphosphate
C) citrate
D) AMP

Question 39

The gluconeogenesis reaction shown below is missing some reactants and products. What class of enzyme catalyzes this reaction?

A) lyase
B) hydrolase
C) transferase
D) oxidoreductase

Question 40

Which enzyme in the glycolysis pathway catalyzes a reaction that requires two enzymes to reverse in the gluconeogenesis pathway?

A) pyruvate kinase
B) phosphofructokinase I
C) pyruvate dehydrogenase
D) glycogen phosphorylase

Question 41

Which of the following molecules would activate phosphofructokinase 1 (PFK1)?

A) NADH
B) AMP
C) ATP
D) pyruvate

Question 42

Which pair of opposite enzymes in the glycolysis and gluconeogenesis pathway are not allosterically regulated but rather regulated by compartmentalization?

A) pyruvate kinase/PEP carboxykinase
B) phosphofructokinase 1/fructose-1,6-bisphosphatase
C) phosphofructokinase 2/fructose-2,6-bisphosphatase
D) hexokinase/glucose-6-phosphatase

Question 43

What triggers the Cori cycle?

A) a buildup of cellular NAD⁺
B) oxygen-limited working muscle cells
C) low levels of glucose in the muscle cells
D) elevated glucagon levels

Question 44

In the elongation of glycogen, activated glucose units are attached to which hydroxyl of the terminal residue of the growing glycogen chain?

A) C-1
B) C-3
C) C-4
D) C-6

Question 45

In the breakdown of glycogen by glycogen phosphorylase, the immediate predominant product is

A) glucose.
B) glucose-1-phosphate.
C) UDP-glucose.
D) glucose-6-phosphate.

Question 46

Which of the following molecules would inhibit the last reaction of glycolysis?

A) ATP
B) glucose
C) AMP
D) NAD⁺

Question 47

The Cori cycle

A) requires both glycolysis and gluconeogenesis pathways.
B) removes lactic acid from liver cells and delivers it to muscle cells.
C) involves the regeneration of NADH equivalents for the working muscles.
D) converts glucose into lactic acid.

Question 48

In the glycogenesis pathway, which enzyme catalyzes the formation of $\alpha$ (1,6) linkages?

A) debranching enzyme
B) glycogen synthase
C) glycogen phosphorylase
D) branching enzyme

Question 49

What controls the activity of the opposing enzymes hexokinase and glucose-6-phosphatase from the glycolysis and gluconeogenesis pathways?

A) levels of ATP
B) cellular compartmentalization and separation of the two enzymes
C) fructose-2,6-bisphosphate concentration
D) phosphorylation of the enzymes

Question 50

Which molecule allosterically activates pyruvate carboxylase?

A) AMP
B) NAD⁺
C) epinephrine
D) acetyl-CoA

Question 51

The enzymes that catalyze the regulated steps in glycolysis are

A) phosphofructokinase, pyruvate dehydrogenase, and lactate dehydrogenase.
B) hexokinase, phosphofructokinase, and pyruvate dehydrogenase.
C) aldolase, phosphofructokinase, and pyruvate kinase.
D) hexokinase, phosphofructokinase, and pyruvate kinase.

Question 52

The branching enzyme of glycogen synthesis is involved in

A) making the $\alpha$ (1,6) branch points.
B) making $\alpha$ (1,4) linkages at the branch points.
C) breaking the $\alpha$ (1,6) branches and smoothing out the glycogen chain.
D) transferring $\backsim$ 3 glucose units from a branch point to the end of a growing glycogen chain.

Question 53

How many high-energy NTP molecules are hydrolyzed for each glucose monomer added to a growing glycogen polymer?

A) 0
B) 1
C) 2
D) 3

Question 54

Which of the following molecules might inhibit the regulated enzymes in glycolysis?

A) NAD⁺
B) ATP
C) AMP
D) fructose-2,6-bisphosphate

Question 55

Which of the following molecules would inhibit the regulated steps in gluconeogenesis?

A) ATP
B) ADP
C) pyruvate
D) NADH

Question 56

In the glycogenesis pathway, what is the leaving group in the last step where glucose is added to the growing glycogen chain?

A) UDP-glucose
B) pi
C) glucose-1-phosphate
D) UDP

Question 57

Which one of the following is involved in the breakdown of glycogen?

A) inorganic phosphate
B) ATP
C) branching enzyme
D) hexokinase

Question 58

The glycogen phosphorylase enzyme

A) makes $\alpha$ (1,4) links at the nonreducing end of glycogen.
B) uses P_i (phosphate) as a nucleophile in the cleavage of glucose units off of the glycogen chain.
C) cleaves the $\alpha$ (1,6) linkages of glucose units in the glycogen polymer.
D) releases free glucose units as its immediate product.

Question 59

The Cori cycle

A) transports pyruvate from working muscles to the liver, where it is converted back to glucose.
B) is important in organisms respiring aerobically.
C) involves the conversion of muscle pyruvate to alanine followed by transport to the liver.
D) relies on functioning lactate dehydrogenase in both muscle and liver tissues.

Question 60

Which hormone slows down glycolysis while stimulating gluconeogenesis through the phosphorylation of phosphofructokinase 2 (PFK2) and fructose-2,6-bisphosphatase?

A) insulin
B) protein kinase
C) ATP
D) glucagon

Question 61

What would happen to cellular glucose-6-phosphate if the pentose phosphate pathway is inhibited?

Question 62

Which statement of the debranching enzyme is true?

A) It catalyzes the addition of free glucose to a nonreducing end of glycogen.
B) Its product is glucose-1-phosphate.
C) It evenly distributes branch points across the glycogen polymer.
D) It is one enzyme with three unique catalytic activities.

Question 63

The hormone insulin stimulates __________ and inhibits __________, leading to a(n) __________ in the glucose levels.

A) glycogen synthase; glycogen phosphorylase; decrease
B) glycogen phosphorylase; glycogen synthase; decrease
C) glycogen synthase; glycogen phosphorylase; increase
D) glycogen phosphorylase; glycogen synthase; increase

Question 64

What class of biomolecule is glycogenin?

A) hormone
B) carbohydrate
C) enzyme
D) lipid

Question 65

In the glycogenesis pathway, the role of the glucose-6-phosphate isomerization reaction is to

A) create a more stable intermediate for the subsequent reaction.
B) decrease the concentration of glucose-6-phosphate, thereby driving the pathway forward.
C) ensure that the charged molecule stays in the cell.
D) prepare the anomeric carbon for nucleophilic attack.

Question 66

In the breakdown of glycogen, the debranching enzyme catalyzes the formation of

A) "glucose-1-phosphate."
B) "glucose."
C) " $\alpha$ (1,6) branched glycogen."
D) "glucose-6-phosphate."

Question 67

Because muscles lack receptors for glucagon, what hormone activates muscle glycogen phosphorylase?

A) insulin
B) adrenaline
C) glycogenin
D) UDP-glucose

Question 68

A patient is found to have a mutated enzyme that results in fewer branch points in glycogen. Which one of the following would best characterize the way in which the patient's glycogen is altered relative to normal glycogen?

A) an increase in the proportion of $\alpha$ (1,6) linkages relative to $\alpha$ (1,4) linkages
B) a change in the stereochemical configuration at the reducing end
C) some $\beta$ (1,4) linkages in place of $\alpha$ (1,4) linkages
D) a decreased ratio of nonreducing to reducing ends

Question 69

Which enzyme catalyzes the following reaction?

A) debranching enzyme
B) glycogen phosphorylase
C) branching enzyme
D) glycogen synthase

Question 70

The role of glycogenin is to

A) catalyze the formation of UDP-glucose.
B) act as a hormone to regulate glucose levels.
C) serve as the origin of the glycogen polymer.
D) enable glycogen to fold properly.

Question 71

The activation of glycogen phosphorylase will lead to a(n) in blood glucose concentrations and is stimulated by the hormone _.

A) decrease; insulin
B) decrease; glucagon
C) increase; insulin
D) increase; glucagon

Question 72

What is the overall net reaction of the pentose phosphate pathway, where glucose-
6-phosphate is entirely converted to CO₂? Please include any cofactors produced for the cell.

Question 73

Why is it important that muscle cells are unresponsive to glucagon?

A) Muscle cells store glycogen for its own energy needs and not the needs of other tissues.
B) The muscles do not store glycogen.
C) The muscles release glucose to other tissues in need.
D) Muscle cells respond to insulin instead.

Question 74

What is the name of the enzyme that removes phosphate groups from the regulated glycogen metabolism enzymes to reverse their activity?

A) phosphorylase kinase
B) protein phosphatase 1
C) insulin
D) protein kinase A

Question 75

McArdle disease is due to a deficiency in muscle glycogen phosphorylase activity. The result of this deficiency is an inability to

A) form $\alpha$ (1,4) linkages in glycogen.
B) form glucose-1-phosphate during the breakdown of glycogen.
C) store glycogen.
D) cleave $\alpha$ (1,6) linkages.

Question 76

What class of enzymes in the oxidative phase of the pentose phosphate pathway is responsible for the production of NADPH?

Question 77

The debranching enzyme does NOT catalyze the

A) formation of $\alpha$ (1,6) linkages.
B) cleavage of $\alpha$ (1,6) linkages.
C) formation of $\alpha$ (1,4) linkages.
D) cleavage of $\alpha$ (1,4) linkages.

Question 78

List the three metabolic molecules that regulate the activity of the pentose phosphate pathway.

Question 79

The branching enzyme

A) couples the formation of glycogen with UDP loss from UDP-glucose.
B) makes $\alpha$ (1,4) linkages with the transfer of seven glucose units.
C) breaks $\alpha$ (1,6) branch points and remakes $\alpha$ (1,4) linkages.
D) catalyzes the cleavage of $\alpha$ (1,4) links and the formation of $\alpha$ (1,6) links.

Question 80

What is the cellular role of glutathione in red blood cells?