Deck 15: Carbohydrate Metabolism I: Major Metabolic Pathways and Their Control

Question 1

The activity of which enzyme would be expected to increase as levels of insulin increase?

A) pyruvate dehydrogenase
B) pyruvate carboxylase
C) glucose 6-phosphatase
D) glycogen phosphorylase
E) PEP carboxykinase

Answer 1

pyruvate dehydrogenase

Question 2

In the glycolytic pathway for conversion of glucose to lactate, an immediate product of the reaction catalyzed by aldolase is

A) fructose 2,6-bisphosphate.
B) fructose 2-phosphate.
C) 3-phosphoglycerate.
D) dihydroxyacetone phosphate.
E) 1,3-diphosphoglycerate.

Answer 2

dihydroxyacetone phosphate.

Question 3

Skeletal muscle glycogen is not a source of blood glucose because skeletal muscle does not contain

A) glucose 6-phosphate dehydrogenase.
B) phosphorylase.
C) phosphoglucomutase.
D) glucokinase.
E) glucose 6-phosphatase.

Answer 3

glucose 6-phosphatase.

Question 4

All of the following are involved in some aspect of galactose metabolism EXCEPT

A) an epimerase.
B) a uridyltransferase.
C) glucose 1-phosphate phosphatase.
D) UDP-glucose.
E) a pyrophosphorylase.

Question 5

Which metabolic process is most markedly impaired in the ABSENCE of insulin?

A) Degradation of glycogen to glucose.
B) Use of acetoacetic acid for energy.
C) Transport of glucose through the muscle cell membranes.
D) Reabsorption of glucose by the renal tubules.

Question 6

Which enzyme is not subject to allosteric regulation?

A) phosphofructokinase
B) hexokinase
C) pyruvate kinase
D) glycogen synthase
E) glucose 6-phosphatase

Question 7

Which of the following compounds is a key intermediate in gluconeogenesis from lactate, pyruvate, alanine, and glutamic acid?

A) ornithine
B) citrate
C) acetyl-CoA
D) oxaloacetate
E) malonyl-CoA

Question 8

Lack of activity of hepatic phosphoglucomutase in a non- fasting subject is most likely to produce a deficiency of

A) pyruvate.
B) ribose 5-phosphate.
C) NADP.
D) NADH.
E) glycogen.

Question 9

Epinephrine stimulates the formation of

A) AMP.
B) the inactive, dephosphorylated form of glycogen synthase.
C) the active, phosphorylated form of phosphorylase.
D) phosphodiesterase.
E) hexokinase.

Question 10

Glycogen phosphorylase catalyzes the following reaction Inorganic phosphate + glycogen (n) -->glucose -phosphate + glycogen (n-) To which enzyme class does it belong?

A) transferase
B) ligase
C) hydrolase
D) lyase
E) isomerase

Question 11

Biotin participates in the reaction catalyzed by

A) phosphoenolpyruvate carboxylase kinase.
B) pyruvate carboxylase.
C) pyruvate dehydrogenase.
D) pyruvate kinase.
E) lactate dehydrogenase.

Question 12

Which of the following reactions IS NOT INVOLVED in regulation of the phosphorylase kinase cascade?

A) formation of cyclic AMP.
B) activation of protein kinase.
C) phosphorylation of certain amino acids of phosphorylase kinase.
D) proteolysis.
E) phosphatases.

Question 13

A deficiency of hepatic phosphoglucomutase would most likely lead to a deficiency of which one of the following cellular components

A) pyruvate.
B) ribose 5-phosphate
C) NADP
D) NADH
E) glycogen

Question 14

Which of the enzymes below acts in the conversion of glucose -6-phosphate to fructose -6-phosphate?

A) kinase
B) isomerase
C) phosphatase
D) mutase
E) dehydrogenase

Question 15

The net products of anaerobic glycolysis are

A) ATP, lactate
B) ATP, pyruvate
C) NAD, lactate
D) ATP, acetyl-CoA

Question 16

An enzyme catalyzing an anaplerotic reaction is

A) pyruvate dehydrogenase.
B) glucose 6-phosphatase.
C) thiolase.
D) citrate synthase.
E) pyruvate carboxylase.

Question 17

The substrates for the phosphoenolpyruvate carboxykinase reaction are

A) alanine and GTP.
B) oxaloacetate and GTP.
C) oxaloacetate and ATP.
D) phosphoenolpyruvate and GTP.
E) pyruvate and GTP.

Question 18

The glucose-alanine cycle serves to

A) transport carbons from skeletal muscle to the liver.
B) transport nitrogen from liver to skeletal muscle.
C) transport carbons and nitrogen from skeletal muscle to the liver.
D) transport carbons and nitrogen from liver to skeletal muscle.
E) transport glucose from skeletal muscle to liver.

Question 19

The malate-aspartate shuttle results in the reduction of intramitochondrial

A) dihydroxyacetone phosphate.
B) pyruvate.
C) NAD.
D) glycerol-3-phosphate
E) all of the above.

Question 20

The substrate for the committed step in glycolysis is

A) glucose
B) fructose 6-phosphate
C) glucose 6-phosphate
D) fructose 1,6-bisphosphate
E) fructose 2,6-bisphosphate

Question 21

All of the following statements about glycolysis and gluconeogenesis are true EXCEPT which one?

A) High concentrations of acetyl-CoA inhibit acetyl-CoA formation from pyruvate and high concentrations of acetyl-CoA stimulate carboxylation of pyruvate.
B) When citrate concentrations in the cytosol are high, PFK-1 activity is inhibited and fructose-1,6-bisphosphatase activity is stimulated.
C) Oxaloacetate is formed from acetyl CoA.
D) Formation of glucose from glycerol does not require the involvement of mitochondria.
E) NADH2 is required for the formation of glucose from pyruvate.

Question 22

In fructose metabolism in the liver, the action of fructokinase on fructose results in the production of

A) fructose 6-phosphate
B) fructose 1-phosphate
C) fructose 1,6-bisphosphate
D) pentose 6-phosphate + carbon dioxide
E) None of the above

Question 23

Binding of epinephrine to muscle cell receptors results directly in increased activity of

A) glycogen synthase.
B) phosphofructokinase.
C) isocitrate dehydrogenase.
D) glucose 6-phosphatase.
E) adenyl cyclase.

Question 24

Which of the following employs the enzyme phosphoenolpyruvate carboxykinase?

A) glycolysis
B) Hexose monophosphate shunt
C) Krebs cycle
D) gluconeogenesis
E) glycogenolysis

Question 25

Two allosterically regulated enzymes on the pathway from lactate to glucose are

A) phosphofructokinase and pyruvate kinase
B) pyruvate carboxylase and fructose 1,6-bisphosphatase
C) fructose 1,6-bisphosphatase and glyceraldehyde 3-phosphate dehydrogenase
D) pyruvate dehydrogenase and pyruvate carboxylase

Question 26

All of the following enzymes have been shown to be defective in one of the glycogen storage diseases EXCEPT which one?

A) glucose 6-phosphatase
B) pyruvate kinase
C) phosphorylase
D) branching enzyme (alpha-1,4 --> alpha-1,6)

Question 27

The principal tissue involved in gluconeogenesis to provide glucose for the resynthesis of muscle glycogen following prolonged exercise is

A) skeletal muscle.
B) brain.
C) kidney.
D) heart muscle.
E) liver.

Question 28

Which statement regarding the control of glycogen metabolism by cyclic AMP is TRUE?

A) Cyclic AMP binds allosterically to both glycogen phosphorylase and glycogen synthase, activating the former and inactivating the latter.
B) Cyclic AMP stimulates the phosphorylation of glycogen phosphorylase and glycogen synthase, activating both.
C) Cyclic AMP stimulates the phosphorylation of glycogen phosphorylase and the dephosphorylation of glycogen synthase, activating the former and deactivating the latter.
D) Cyclic AMP stimulates the phosphorylation of both glycogen phosphorylase and glycogen synthase, activating the former and deactivating the latter.
E) Cyclic AMP increases the intracellular concentration of calcium ions which stimulates the dephosphorylation of both glycogen phosphorylase and glycogen synthase.

Question 29

Increased levels of ATP inhibit which pair of enzymes?

A) glyceraldehyde 3-phosphate dehydrogenase and enolase
B) lactate dehydrogenase and triose phosphate isomerase
C) phosphofructokinase and pyruvate kinase
D) phosphofructokinase and glucose 6-phosphate isomerase
E) glucokinase and phosphoglucomutase

Question 30

Which one of the following molecules is a negative allosteric effector of phosphofructokinase?

A) Succinic acid
B) ADP
C) Oxaloacetate
D) Citrate
E) All of the above

Question 31

Which enzyme uses inorganic phosphate as a substrate?

A) glucose 6-phosphatase.
B) phosphofructokinase.
C) glucokinase.
D) glucose 6-phosphate dehydrogenase.
E) glyceraldehyde 3-phosphate dehydrogenase.

Question 32

UDP-glucose is intermediate in each of these conversions EXCEPT which one?

A) glucose to glycogen
B) fructose to glycogen
C) galactose to glycogen
D) glycogen to glucose
E) galactose to glucose

Question 33

Which process is NOT increased in the presence of insulin?

A) gluconeogenesis in liver
B) glucose transport into adipose tissue
C) protein synthesis in muscle
D) lipogenesis in adipose tissue
E) glycogen synthesis in muscle

Question 34

A true statement concerning phosphofructokinase- (PFK-) and fructose-,-bisphosphatase is that

A) PFK-1 catalyzes the fastest step in glycolysis.
B) PFK-1 catalyzes a reversible step in both glycolysis and gluconeogenesis.
C) PFK-1 is not found in red blood cells.
D) Fructose-1,6-bisphosphatase requires ATP for energy.
E) Fructose-2,6-bisphosphate is a positive allosteric regulator of PFK-1 and is a negative allosteric regulator of fructose-1,6-bisphosphatase.

Question 35

Which statement concerning phosphorylase is FALSE?

A) The active enzyme catalyzes the reaction: (glucose)n + Pi -> (glucose)n-1 + Glucose-1-P
B) The enzyme is activated by phosphorylation.
C) Phosphorylation of phosphorylase in muscle is controlled by glucagon.
D) The phosphorylation of phosphorylase is catalyzed by a protein kinase.
E) The phosphorylation of phosphorylase increases at higher concentrations of cAMP

Question 36

Which is an unlikely metabolic fate of glucose--phosphate in muscle?

A) Conversion to fructose-6-phosphate.
B) Conversion to glucose-1-phosphate.
C) Conversion to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
D) Hydrolysis to glucose.
E) Conversion to lactate.

Question 37

The biosynthesis of glycogen from glucose -phosphate

A) is catalyzed by glycogen phosphorylase.
B) requires UTP.
C) is stimulated by a low energy charge.
D) occurs in the mitochondrial matrix.
E) is stimulated by increased levels of cyclic AMP.

Question 38

Phosphorylase is activated most directly by

A) epinephrine.
B) phosphorylase kinase.
C) phosphorylase phosphatase.
D) cAMP.
E) glucagon.

Question 39

The activity of which enzyme is controlled by phosphorylation and dephosphorylation of serine residues?

A) glucokinase
B) PEP carboxykinase
C) phosphofructokinase
D) 3-phosphoglyceraldehyde dehydrogenase
E) glycogen phosphorylase

Question 40

All of the following sugars require the action of phosphofructokinase for their metabolism to carbon dioxide and water EXCEPT

A) glucose.
B) galactose.
C) mannose.
D) maltose.
E) fructose.

Question 41

Which is a positive allosteric effector of phosphofructokinase?

A) glucose 6-phosphate
B) acetyl-CoA
C) citrate
D) fructose 2,6-bisphosphate
E) ATP

Question 42

Glycolysis will cease if

A) the concentration of cAMP is decreased.
B) phosphofructokinase is activated.
C) mitochondria are not present in the cell.
D) NADH is not oxidized.

Question 43

Insulin

A) stimulates the phosphodiesterase enzyme which breaks down cAMP.
B) decreases the concentration of fructose-2,6-bisphosphate in liver.
C) inhibits hepatic glycolysis.
D) stimulates glucose transport into the liver.
E) has the same effect on glycolysis in the liver as glucagon.

Question 44

For which glycolytic enzyme is inorganic phosphate a substrate?

A) aldolase
B) glucose-6-phosphatase
C) enolase
D) glyceraldehyde-3-phosphate dehydrogenase
E) pyruvate kinase

Question 45

Biotin participates in the reaction catalyzed by

A) phosphoenolpyruvate carboxylase kinase.
B) pyruvate carboxylase
C) pyruvate dehydrogenase.
D) pyruvate kinase.
E) lactate dehydrogenase.

Question 46

In glycogen, what types of linkages are present between the glucose units?

A) Beta-1,4-linkages only
B) Beta-1,4 and beta-1,6 linkages
C) Alpha-1,4 linkages only
D) Alpha-1,4 and alpha-1,6 linkages
E) Beta-1,3 linkages

Question 47

The glycogen branching enzyme is classified as

A) a glycogen phosphorylase.
B) a uridine diphosphate glucose-glycogen glucosyl transferase.
C) an amylo (1,4 --> 1,6)
D) a beta-amylase.
E) an alpha-amylase.

Question 48

Glycogen phosphorylase P (the phosphorylated form) may be activated by

A) ATP.
B) AMP.
C) glucose-1-phosphate.
D) glucose-6-phosphate.
E) fructose-1,6-biphosphate.

Question 49

Which of the following enzymes reactivates inactive liver phosphorylase?

A) glycogen synthase
B) glycogen branching enzyme
C) amylo-(1,6)
D) phosphorylase kinase

Question 50

Which statement about gluconeogenesis is correct?

A) The acetate group of acetyl-CoA is used for the net synthesis of glucose.
B) It occurs primarily in skeletal muscle.
C) It occur through reversal of the reactions of glycolysis.
D) Lactate and alanine can both serve as substrates.
E) ATP is not required.

Question 51

Two enzymes specifically required for gluconeogenesis from lactate but not from glycerol are

A) pyruvate kinase and phosphoglycerate kinase.
B) pyruvate carboxylase and phosphoenolpyruvate carboxykinase.
C) glucose 6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase.
D) fructose 1,6-bisphosphatase and phosphofructokinase-1.
E) glyceraldehyde 3-phosphate dehydrogenase and aldolase.

Question 52

The disaccharide lactose is composed of

A) galactose and mannose.
B) glucose and mannose.
C) glucose and galactose.
D) glucose and glucosamine.
E) glucose and fructose.

Question 53

A decrease in the ATP:ADP ratio would result in

A) a decrease in phosphofructokinase activity.
B) a decrease in the rate of electron transport and oxidative phosphorylation.
C) an increase in the net flux of intermediates through the glycolytic pathway.
D) a decrease of isocitrate dehydrogenase activity.
E) none of the above

Question 54

The actions of glycogen phosphorylase and the debranching enzyme on glycogen results in which of the following product or products?

A) glucose 6-phosphate
B) glucose 1-phosphate and glucose
C) UDP-glucose
D) glucose 6-phosphate and glucose
E) UDP-glucose and glucose

Question 55

For gluconeogenesis

A) The enzymes that catalyze the 3 irreversible steps of glycolysis are used in the process of glucose synthesis.
B) The enzymatic reactions are carried out in 3 different subcellular compartments.
C) The brain and testis are the most important tissues involved.
D) No high energy phosphate compounds are involved.

Question 56

Which liver enzyme is required to form glucose from both glycogen and lactate?

A) pyruvate carboxylase
B) fructose-1, 6-bisphosphatase
C) glucose-6-phosphatase
D) phosphorylase a
E) phosphoglucomutase

Question 57

The following enzyme(s) is/are required to synthesize phosphoenol_pyruvate from pyruvate in gluconeogenesis:

A) pyruvate kinase
B) pyruvate carboxylase and phosphoenolpyruvate carboxykinase
C) Fructose-1,6-bisphosphatase and glucose-6-phosphatase
D) pyruvate dehydrogenase
E) phosphoenolpyruvate dehydrogenase and pyruvate alpha_ketolase

Question 58

Which of the following enzymes forms alpha-, linkages in glycogen?

A) glycogen synthase
B) glycogen branching enzyme
C) amylo-(1,6)
D) phosphorylase kinase

Question 59

Glucagon plays a homeostatic role by

A) being released from the pancreas in response to elevated blood glucose levels and then activating the liver phosphorylase system.
B) being released from the pancreas in response to lowered blood glucose levels and then activating the liver phosphorylase system.
C) stimulating the release of glucose residues from muscle glycogen during periods of intense muscular activity.
D) activating adenylate cyclase in skeletal muscle cells.
E) facilitating glucose uptake into skeletal muscle.

Question 60

Which of the following are activators of glycolysis AND inhibitors of gluconeogenesis? 1. AMP 2. ATP 3.citrate 4..fructose 2,6-bisphosphate 5. fructose 1,6-bisphosphate

A) 1 and 3
B) 2 and 4
C) 3 and 5
D) 4 and 1
E) 5 and 3

Question 61

Glycolysis is only partially reversible because of energy barriers at the reactions catalyzed by

A) hexokinase, triose phosphate isomerase, and pyruvate kinase.
B) phosphofructokinase, aldolase, and lactate dehydrogenase.
C) hexokinase, pyruvate dehydrogenase, and phosphoenolpyruvate carboxykinase.
D) hexokinase, phosphofructokinase, and pyruvate kinase.
E) hexokinase, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase.

Question 62

An increase in glucagon will cause

A) an increase in liver glycogenolysis.
B) a decrease in blood glucose.
C) an inactivation of liver adenyl cyclase.
D) an increase in muscle glycogenesis.

Question 63

A substrate which transfers phosphate directly to ADP is

A) 3-phosphoglycerate.
B) 3-phosphoglyceraldehyde.
C) phosphoenolpyruvate.
D) fructose 1,6-bisphosphate.
E) 2-phosphoglyceric acid.

Question 64

The enzyme that catalyzes the conversion of fructose-l,-bisphosphate to fructose--phosphate + Pi is classified as

A) an oxidoreductase.
B) a transferase.
C) a hydrolase.
D) a lyase.
E) a ligase.

Question 65

Which statement about glycolysis is TRUE?

A) The first step for which ATP is required is catalyzed by phosphofructokinase.
B) The rate of glycolysis in the absence of oxygen is usually less than the rate in the presence of oxygen.
C) The phosphoglycerate kinase reaction is reversible under physiological conditions but the hexokinase reaction is not.
D) The product of the reaction catalyzed by triose phosphate isomerase is phosphoenolpyruvate.
E) The conversion of pyruvate to lactate requires NAD.

Question 66

All of the following metabolic conditions favor the conversion of pyruvate to glucose EXCEPT

A) an active form of pyruvate carboxylase.
B) a rapid rate of fatty acid oxidation.
C) an energy charge near 1.0.
D) a low level of active phosphoenolpyruvate carboxykinase.
E) an inhibited pyruvate dehydrogenase complex.

Question 67

Which of the following is an enzyme which catalyzes a freely reversible reaction under physiological conditions?

A) glucose 6-phosphatase
B) phosphofructokinase
C) aldolase
D) phosphoenolpyruvate carboxykinase
E) fructose bisphosphatase

Question 68

All the following statements about the enzyme glyceraldehyde -phosphate dehydrogenase are correct EXCEPT

A) it conserves the energy of an oxidation reaction as a high energy phosphate bond.
B) the enzyme forms a covalent high energy intermediate in the reaction.
C) NAD is required for the enzyme to function.
D) ATP is a product of the reaction.
E) phosphate is consumed in the reaction.

Question 69

All of the following statements concerning gluconeogenesis are correct EXCEPT which one?

A) gluconeogenesis from lactate occurs in both mammalian liver and muscle.
B) One mole of glucose is produced from two moles of lactate.
C) Given ATP, all the reactions of gluconeogenesis can occur in the absence of air.
D) Although a net of two molecules of ATP are generated per molecule of glucose converted to lactate, six molecules of ATP (or its equivalent) are required to synthesize one molecule of glucose from lactate.
E) Photosynthesis in green plants utilizes part of the gluconeogenic pathway for hexose synthesis.

Question 70

What is the primary process by which epinephrine increases blood sugar?

A) synthesis of carbohydrate from fat
B) absorption of carbohydrate from the digestive tract
C) liver glycogenesis
D) liver glycogenolysis
E) glyconeogenesis

Question 71

All of the following can stimulate the activity of muscle glycogen phosphorylase EXCEPT

A) calcium ions.
B) epinephrine.
C) cyclic AMP.
D) phosphorylase kinase.
E) glucagon.

Question 72

Glucocorticoids such as cortisol and corticosterone have distinct effects on hepatic carbohydrate metabolism, such as promoting gluconeogenesis and glycogen deposition. The likely mechanism of these effects involves

A) binding of glucocorticoids to liver cell membrane receptors with concomitant activation of adenylate cyclase.
B) acute stimulation of enzymes in the pathways of gluconeogenesis and glycogenesis.
C) direct inhibition of enzymes participating in glycolysis and glycogenesis.
D) induction of new enzyme synthesis for enzymes in the pathways of gluconeogenesis and glycogen synthesis.

Question 73

The glycerol phosphate shuttle

A) results in production of dihydroxyacetone phosphate in the matrix of mitochondria.
B) transfers electrons from cytosolic NADH to the respiratory chain of mitochondria.
C) inhibits glycolysis.
D) supports phosphorylation of three moles of ADP per mole of cytosolic NADH oxidized.
E) uses 3-phosphoglyceric acid as a substrate.

Question 74

If liver glucose -phosphatase were deficient, what would best characterize the expected change in metabolism relative to the normal state?

A) increased energy supply to the brain.
B) hyperglycemia after a normal meal.
C) depletion of glycogen stores in liver.
D) hypoglycemia one or two hours after a meal.

Question 75

Cyclic AMP

A) has a phosphodiester bond between C-5 and C-2 carbons of the ribose moiety.
B) inhibits glucose-6-phosphatase.
C) is degraded in response to high glucagon levels.
D) is synthesized directly from AMP.
E) modulates the level of fructose 2,6 bisphosphate.

Question 76

Which reaction is catalyzed by glycogen synthase?

A) UTP + glucose 1-P --> UDP-glucose + PPi
B) UDP glucose + glycogenin --> PPi + glycogenn+1
C) UDP glucose + glycogenin --> UMP + Pi + glycogenn+1
D) glycogenin + UDP-glucose --> glycogenn+1 + UDP
E) glucose 6-P + glycogenin --> Pi + glycogenn+1

Question 77

During the breakdown of glycogen, free glucose is formed from

A) the reducing end.
B) the non-reducing end.
C) glucose residues in an alpha 1-->4 linkage to the chain.
D) glucose residues in an alpha 1-->6 linkage to the chain.
E) hydrolysis of glucose 1-phosphate.

Question 78

All of the following statements about galactose and its metabolism are true EXCEPT:

A) A UDP-glucose molecule is an intermediate in galactose metabolism.
B) Galactokinase uses ATP as substrate.
C) Galactose is a ketose.
D) Galactose is converted to glucose in the liver.
E) Digestion and absorption of lactose results in an increase in blood glucose concentrations.

Question 79

In the following pathway for conversion of glucose to pyruvate, what is compound X? glucose --> --> --> --> glyceraldehyde -phosphate --> X --> phosphoglycerate --> --> --> pyruvate

A) glyceraldehyde 2- phosphate
B) 2-phosphoglycerate
C) 1,3-bisphosphoglycerate
D) 1-phosphoglycerate
E) 2,3-bisphosphoglycerate

Question 80

All of the following statements concerning the conversion of pyruvate to glucose in mammals are true EXCEPT

A) electrons are shuttled from mitochondria to the cytoplasm during this conversion.
B) high levels of cellular ATP results in stimulation of this process.
C) GTP is involved in this process.
D) only one regulated enzyme is involved in the overall conversion of pyruvate to glucose.
E) some of the enzymes of glycolysis participate in the conversion.