Deck 21: Metabolic Interrelationships

Question 1

During heavy exercise, the Cori Cycle employs the gluconeogenic pathway in the liver and the glycolytic pathway in muscle. The major metabolites transported by blood to connect these pathways are

A) glucose and pyruvate
B) alanine and lactate
C) glucose and alanine
D) glucose and lactate
E) palmitate and glycerol

Answer 1

glucose and lactate

Question 2

When is hepatic glycogenolysis a primary source of blood glucose?

A) Well-fed state, 2-3 hours postprandial
B) Early fasted state, 3-12 hours postprandial
C) Fasted state, 12-36 hours postprandial
D) Early refed state, 0-2 hours after refeeding

Answer 2

Early fasted state, 3-12 hours postprandial

Question 3

Initially insulin increases the

A) uptake of glucose by the liver.
B) uptake of glucose by erythrocytes.
C) uptake of glucose by adipose tissue.
D) level of cAMP in adipose tissue.
E) rate of glycogen breakdown in the liver.

Answer 3

uptake of glucose by adipose tissue.

Question 4

During a period of fasting, muscle will derive the most energy from the catabolism of

A) tyrosine.
B) cysteine.
C) lysine.
D) leucine.
E) tryptophan.

Question 5

Which reaction does NOT occur in muscle?

A) synthesis of glucose from alanine
B) oxidation of beta-hydroxybutyric acid
C) oxidation of lactic acid
D) glycogenolysis
E) formation of glutamine from glutamate

Question 6

Free glycerol

A) is not a gluconeogenic substrate and is readily excreted in the urine.
B) is potentially gluconeogenic, and its point of entry into the gluconeogenic pathway is as pyruvate.
C) cannot support the net synthesis of glucose, because glycerol cannot be phosphorylated in vivo.
D) is potentially gluconeogenic, and its point of entry into the gluconeogenic pathway is as triose phosphate.
E) is ketogenic because it is derived from the catabolism of triacylglycerols.

Question 7

Long-chain fatty acids in heart

A) are minor energy sources.
B) are usually converted to triglycerides.
C) are converted to ketones.
D) are obtained by synthesis in mitochondria.
E) provide the energy for most ATP synthesis.

Question 8

Why do type II diabetics generally not develop ketoacidosis?

A) It takes 2 days of starvation before ketone bodies are synthesized
B) Ketone bodies are not needed for the brain in this case
C) The decrease in lipoproteins prevents transport of ketone bodies
D) There is enough residual insulin to suppress lipolysis
E) There is not enough insulin to promote lipid synthesis

Question 9

During anaerobic exercise, which reaction would be most active in the exercising muscle?

A) oxidative decarboxylation of isocitrate to α-ketoglutarate
B) oxidative decarboxylation of a-ketoglutarate to succinyl CoA
C) oxidative decarboxylation of pyruvate to acetyl CoA
D) conversion of succinate to fumarate
E) conversion of pyruvate to lactic acid

Question 10

Which of the following is most consistent with a defective malate-aspartate shuttle

A) Abnormally large rise in glucose consumption when oxygen is admitted to an anaerobic incubation of tissue
B) Diminished ability of mitochondria to oxidize isocitrate
C) Large increase in the pyruvate:lactate ratio following exercise
D) Abnormally large decrease in intracellular pH of muscle during exercise
E) Partial uncoupling of oxidative phosphorylation

Question 11

Blood glucose levels are

A) decreased by cortisol
B) decreased by glucagon
C) increased by epinephrine
D) increased by insulin
E) decreased by testosterone

Question 12

A 25 year old, healthy male has begun a treadmill exercise program. He has set the treadmill to a fast pace and has begun to run. As his physical activity continues for several minutes his heart rate would be expected to increase and the levels of _______________ would be expected to rise significantly in his blood.

A) aspartic acid
B) citric acid
C) lactic acid
D) pyruvic acid
E) uric acid

Question 13

What change from normal is likely to result from the ingestion of ethanol?

A) increased reduction of pyruvate
B) increased conversion of beta-hydroxybutyrate to acetoacetate
C) decreased ketogenesis due to lack of acetyl-CoA
D) increased production of oxaloacetate from malate
E) increased production of dihydroxyacetone phosphate from glycerol phosphate

Question 14

All of the following are true EXCEPT which one?

A) Resting muscle produces negligible lactic acid.
B) Resting liver only minimally oxidizes lactate.
C) Monomers of a starchy meal, not followed by vigorous exercise end up as glycogen in liver, skeletal or heart muscle.
D) Working muscle oxidizes fatty acids to lactate.
E) The central control points in glycolysis are hexokinase, phosphofructokinase and pyruvate kinase.

Question 15

The major source of glutamine in blood during short term fasting is

A) oxidation of leucine by adipose, heart, and skeletal muscle.
B) oxidation of isoleucine and valine released from muscle protein.
C) amino acid breakdown in brain and other tissues.
D) amidation of glutamate released from muscle protein.
E) amidation of glutamate from the blood by liver.

Question 16

In starvation, the body makes a major adaptation to conserve its protein stores

A) by synthesizing essential amino acids to meet the body demands.
B) by neutralizing metabolic by-products such as urea, creatinine.
C) by utilization of ketone bodies, i.e., non-protein derived energy sources, for the metabolic needs of the brain and nervous system.
D) by the incomplete combustion of 2-carbon molecules derived from adipose stores.

Question 17

Insulin induces the hepatic synthesis of

A) pyruvate kinase, some of the transaminases, ATP-citrate lyase
B) phosphofructokinase, glucose 6-phosphatase, isocitric dehydrogenase
C) acetyl-CoA carboxylase, glucokinase, fatty acid synthase
D) glucose 6-phosphatase, phosphorylase, PEP carboxykinase
E) glycerol kinase, hormone sensitive lipase, pyruvate dehydrogenase

Question 18

An amino acid which is ketogenic but not glucogenic

A) can provide carbons for the net synthesis of glucose.
B) can enter the Krebs cycle at the level of oxaloacetate.
C) can provide carbons for the synthesis of fatty acids.
D) cannot be oxidized through the Krebs cycle.
E) None of the other answers is correct.

Question 19

A normal adult is placed on a diet containing adequate amounts of all essential nutrients but no tyrosine. Which statement regarding this individual is true?

A) The person would be in negative nitrogen balance.
B) There would be a transient period of negative nitrogen balance followed by nitrogen equilibrium.
C) Urea excretion would increase above that in the pre-diet period because protein synthesis could not continue.
D) The person would be in nitrogen equilibrium.
E) The rate of synthesis of phenylalanine would decrease compared to that in the pre-diet period.

Question 20

Direct precursors of lactose are

A) UDP-glucose and fructose.
B) UDP-glucose and galactose.
C) glucose 1-phosphate + galactose 6-phosphate.
D) UDP-galactose + fructose.
E) UDP-galactose + glucose

Question 21

In the transition from a well-fed to a fasting state, which enzyme in liver cells is most likely to decrease in amount?

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

Question 22

How does a lack of oxygen most directly cause a decrease in the activity of the Krebs cycle?

A) The synthesis of lactate from pyruvate is inhibited.
B) High levels of malonyl CoA inhibit carnitine acyl transferase I.
C) Electron transport is interrupted.
D) Circulating levels of epinephrine are increased.
E) The rate of glycogenolysis decreases.

Question 23

Glycogen breakdown in which of the following tissues can be used to support blood glucose levels during periods of fasting?

A) skeletal muscle
B) adipose tissue
C) liver
D) brain
E) spleen

Question 24

Which of the following reactions gives the greatest yield of high energy phosphate?

A) palmitoyl-CoA --> 8 acetyl-CoA
B) 8 acetyl-CoA --> 16 carbon dioxide
C) glucose --> 2 pyruvate
D) 2 pyruvate --> 2 acetyl-CoA + 2 carbon dioxide
E) 2 lactate --> 2 pyruvate

Question 25

The enzyme that is termed the glucose sensor of the liver is

A) phosphofructokinase.
B) glucose 6-phosphatase.
C) glucose 6-phosphate dehydrogenase.
D) glycogen phosphorylase a

Question 26

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 27

Which amino acid is most important as a non-toxic form in which ammonia is transported in the bloodstream?

A) asparagine
B) glutamine
C) aspartate
D) ornithine
E) glutamate

Question 28

Exercise intolerance would be MOST likely to accompany a deficiency of

A) Phosphorylase
B) Fructose-l ,6?bisphosphatase
C) Glucokinase
D) Erythrocyte pyruvate kinase
E) Muscle glucose-6-phosphatase

Question 29

In the liver, insulin affects each of the following EXCEPT which one?

A) Lipogenesis from acetyl-CoA
B) Rate of glycolysis
C) Transport of glucose into cells
D) Oxidation of fatty acids
E) Gluconeogenesis

Question 30

All of the following statements concerning the fate of lactate produced by skeletal muscle during strenuous exercise are true EXCEPT which one?

A) It diffuses out of the muscle cell into the surrounding interstitial fluid.
B) It is converted to glucose in the liver.
C) It is oxidized to carbon dioxide and water in skeletal muscles.
D) It is utilized as an energy source by cardiac muscles.

Question 31

In skeletal muscle during strenuous exercise, the NADH produced in the reaction catalyzed by glyceraldehyde 3- phosphate dehydrogenase is reoxidized primarily by

A) malate dehydrogenase.
B) lactate dehydrogenase.
C) pyruvate dehydrogenase.
D) isocitrate dehydrogenase.
E) glucose 6-phosphate dehydrogenase.

Question 32

In untreated insulin-dependent diabetes, all these differences from the normal state are observed EXCEPT

A) transport of glucose into adipose tissue is increased.
B) gluconeogenesis is increased.
C) glycogen breakdown in liver is increased.
D) lipolysis in adipose tissue is increased.
E) ketogenesis is increased.

Question 33

Oxidation of fatty acids in liver mitochondria may facilitate gluconeogenesis by

A) supporting the phosphorylation of ADP.
B) forming acetyl CoA which can contribute to the net synthesis of glucose.
C) reducing FAD and NADP⁺.
D) transporting carnitine into mitochondria.
E) decreasing the dependence of phosphorylation of ADP on oxygen consumption.

Question 34

Which of the following is/are expected to occur during and immediately following the absorption of a meal?

A) Acetyl-CoA carboxylase is inhibited by the presence of increased amounts of citrate in the cytosol.
B) Mitochondrial concentrations of oxaloacetate are depressed.
C) Lipoprotein lipase is decreased in amounts.
D) Serum circulating ketone bodies are increased in amounts.
E) Hormone-sensitive lipase is decreased in activity.

Question 35

In the lactating mammary gland, which are the immediate precursors for the formation of lactose?

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

Question 36

The most direct point of entry for alanine into the gluconeogenic pathway is as

A) oxaloacetate.
B) pyruvate.
C) glyceraldehyde 3-phosphate.
D) dihydroxyacetone phosphate.
E) 2-ketobutyrate.

Question 37

The Cori Cycle, glucose --> 2 lactate + 2ATP (Muscle) and 2 lactate + 6 ATP --> glucose (Liver), is important because

A) there is a net destruction of ATP, restoring the energy balance between liver and muscle.
B) it results in the net generation of glucose in the liver and ATP in the muscles without the build up of high lactate levels.
C) it enables muscle mass to be used for energy in conditions of extreme starvation.
D) it serves to prevent lactate levels from dropping too low in the blood, which would impair brain function.
E) it enables glucose 6-phosphate to be transported across the liver cell plasma membrane.

Question 38

Adipose tissue contains little or none of which one of the following enzymes?

A) glucose 6-phosphate dehydrogenase
B) hormone-sensitive lipase
C) glyceraldehyde 3-phosphate dehydrogenase
D) glycerol kinase
E) glycerol phosphate dehydrogenase

Question 39

A positive nitrogen balance would be expected in all of the following conditions EXCEPT

A) growing children.
B) pregnancy.
C) consumption of a diet with increased protein.
D) recovery from trauma or surgery.

Question 40

During periods of prolonged fasting in a normal, healthy individual, blood glucose levels are maintained by gluconeogenesis. The carbons utilized for glucose synthesis under these circumstances are derived primarily from

A) glycogen.
B) fatty acids.
C) heteropolysaccharides.
D) nucleic acid.
E) protein.

Question 41

What determines that the metabolism of amino acids in the liver is low during the well-fed state?

A) Amino acids are not absorbed from the diet
B) Amino acids are not removed from portal blood flow
C) Endogenous inhibitors are synthesized
D) The liver participates in the Cori Cycle
E) The necessary catabolic enzymes have high Kms

Question 42

Physiological conditions that promote the synthesis of ketone bodies also promote the

A) oxidation of fatty acids in erythrocytes.
B) oxidation of glucose in adipose tissue.
C) synthesis of amino acids in skeletal muscle.
D) synthesis of fatty acids in cardiac muscle.
E) synthesis of glucose in liver.

Question 43

Lactate production during muscular contraction is ascribed in part to

A) an overproduction of acetyl-CoA not metabolized in the Krebs cycle.
B) an underproduction of acetyl-CoA for utilization in the Krebs cycle.
C) temporary anaerobic state in muscle.
D) overabundance of ATP produced by metabolism through the Krebs cycle.

Question 44

Why do tumors tend to use glycolysis as the source of most of their ATP?

A) Angiogenesis delivers a large amount of glucose
B) Lack of oxygen induces HIF-1a
C) These cells have fewer mitochondria
D) These cells do not have enzymes of electron transport
E) These cells do not have TCA enzymes

Question 45

Which of the following statements about catabolism of body proteins during starvation is correct?

A) The breakdown of proteins occurs spontaneously, without the need for enzyme catalysis.
B) The amino acids resulting from protein breakdown are either reused as such or are deaminated and their carbon skeletons used as a source of energy.
C) The first amino acids to be catabolized are derived from the protein storage depot in liver.
D) The amino acids derived are used primarily for synthesis of fatty acids.
E) The initial steps in the process involve cleavage of the amino acid side chains from polypeptides.

Question 46

The largest amount of glycogen in humans is stored in

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

Question 47

Nitrogen is carried from skeletal muscle to the liver in the post-absorptive state primarily in the form of 1. arginine 2. glutamine 3. alanine 4 . Serine 5 . histidine

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

Question 48

The substrate normally utilized as the major source of energy by the brain is

A) triglycerides.
B) fatty acids.
C) ketone bodies.
D) amino acids.
E) glucose.

Question 49

The mature erythrocyte

A) uses fatty acids as the main source of energy.
B) reduces NADP⁺ to NADPH largely through the hexose monophosphate shunt.
C) produces bisphosphoglycerate (DPG) largely via the hexose monophosphate shunt.
D) synthesizes proteins.
E) contains relatively extensive endoplasmic reticulum.

Question 50

The principal source of NH₄⁺ for glutamine synthesis in muscle is

A) glutamate.
B) adenosine.
C) inosine.
D) urea.
E) carbamoyl phosphate.

Question 51

The liver normally uses which one of the following for its own energy needs in the fed state?

A) Free fatty acids
B) Amino acids
C) glucose
D) Glycerol

Question 52

Certain amino acids can increase the concentration of blood glucose because

A) they can be oxidized via the Krebs cycle.
B) they are essential.
C) their carbon chains can be converted to intermediates in the Krebs cycle.
D) their carbon chains can be converted to acetyl-CoA.
E) they can undergo transamination reactions.

Question 53

Which reaction in the liver should be stimulated most in a starving individual?

A) serine dehydratase reaction
B) pyruvate dehydrogenase reaction
C) acetyl CoA carboxylase reaction
D) citrate lyase reaction
E) conversion of oxaloacetate to aspartate

Question 54

Which amino acid is not taken up well by liver, and must be supplied by its essential amino acid precursor?

A) Arginine
B) Cysteine
C) Glycine
D) Serine
E) Tyrosine

Question 55

The enzyme in muscle which is most directly stimulated by epinephrine is

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

Question 56

The major source of energy in the heart of a runner who has just won a 1, 000 meter race would be

A) glycogen.
B) phospholipids.
C) plasma glucose.
D) plasma amino acids.
E) plasma fatty acids.

Question 57

The brain utilizes ketone bodies rather than fatty acids because

A) ketone bodies are a more efficient fuel.
B) brain tissue cannot metabolize fatty acids to any significant degree.
C) ketone bodies can be converted into glucose.
D) none of the above.

Question 58

The principal store of metabolic energy available during long term fasting or starvation is

A) muscle glycogen.
B) liver glycogen.
C) muscle protein.
D) adipose tissue triacylglycerol.

Question 59

During exercise epinephrine and glucagon levels are elevated and insulin levels are depressed. Under these conditions, which enzyme should be activated?

A) glycogen synthase
B) fatty acid synthase
C) hormone-sensitive lipase
D) acetyl CoA carboxylase
E) ATP-citrate lyase

Question 60

In the long term fasting state, a large proportion of the energy of the brain is derived from circulating

A) acetoacetyl-CoA.
B) acetone.
C) beta-hydroxybutyrate.
D) oxalacetate.
E) malonic acid.

Question 61

Increased levels of ATP in the fed state helps to channel acetyl CoA into fat synthesis by inhibiting

A) citrate synthase.
B) isocitrate dehydrogenase.
C) citrate lyase.
D) acetyl CoA carboxylase.
E) palmitate thiokinase (CoA synthase).

Question 62

An increased concentration of intracellular AMP in skeletal muscle would cause

A) an increase in glycogen synthesis.
B) rapid glycolysis.
C) rapid gluconeogenesis.
D) a shut down of the TCA cycle.
E) an inhibition of phosphofructokinase.

Question 63

A high insulin to glucagon ratio indicates

A) starvation or low carbohydrate diet.
B) nutrient storage and protein anabolism.
C) mobilization of nutrients and protein catabolism.
D) the effects of severe infection.

Question 64

Which statement about the Cori cycle is TRUE?

A) All of the component reactions occur in the liver.
B) Lactate from muscle is used in the liver as a gluconeogenic substrate.
C) Free glucose, produced from glycogen in skeletal muscle, is utilized for the synthesis of glycogen in the liver.
D) It is the cycle in the liver by which glycogen is synthesized from and degraded to glucose 1-phosphate.
E) All of the component reactions occur in skeletal muscle.

Question 65

In an uncontrolled diabetic which of the following amino acids would yield both glucose and ketone bodies?

A) Alanine
B) Tyrosine
C) Proline
D) Glycine
E) Leucine

Question 66

Which of the following is the major substrate used for energy by resting muscle?

A) fructose
B) nonesterified fatty acids
C) glycerol
D) beta-hydroxybutyrate
E) lactate

Question 67

Which of the following tissues would have the highest levels of gluconeogenesis during starvation?

A) brain
B) red blood cells
C) adipose tissue
D) liver
E) muscle

Question 68

ypoglycemia associated with ethanol intoxication is accompanied by:

A) Decreased lactate/pyruvate ratio
B) Elevated blood pyruvate
C) Elevated NADH/NAD⁺ ratio
D) Increased activity of PEP carboxykinase
E) Increased activity of pyruvate carboxylase

Question 69

In the metabolism of adipose triacylglycerols, insulin stimulates the activity of each of the following proteins EXCEPT

A) 3',5'-AMP phosphodiesterase.
B) fatty acid synthase.
C) glucose transporter 4.
D) hormone-sensitive lipase.
E) lipoprotein lipase.

Question 70

What change from normal will accompany the ingestion of sufficient ethanol to make an individual drunk?

A) activation of pyruvate dehydrogenase
B) increased rate of gluconeogenesis from pyruvate
C) increased concentration of lactate in plasma
D) decreased ratio of NADH/NAD⁺ in liver
E) increased activity of alpha-ketoglutarate dehydrogenase

Question 71

The major pathway by which mature adult red cells generate ATP is

A) aerobic metabolism.
B) anaerobic glycolysis.
C) hexose monophosphate shunt activity.
D) generation of 2,3-diphosphoglycerate.
E) lipid peroxidation.

Question 72

ketosis may develop as a result of which of the circumstances below?

A) glucose synthesis from fatty acids during glucose deprivation
B) acute attack of gout
C) carnitine transferase I deficiency
D) hyperglycemia
E) fat mobilization to support gluconeogenesis

Question 73

The glucose-alanine cycle functions chiefly in the exchange of carbon and nitrogen between

A) kidney and liver.
B) muscle and brain.
C) gut and liver.
D) liver and muscle.
E) muscle and kidney.

Question 74

What is the main source of carbon atoms for ketone bodies in a diabetic?

A) heart
B) liver
C) brain
D) adipose
E) skeletal muscle

Question 75

During contraction, phosphocreatine is used

A) to phosphorylate ADP.
B) to phosphorylate glycogen.
C) directly in contraction.
D) to activate phosphofructokinase.
E) to phosphorylate fructose 6-phosphate.

Question 76

Which statement regarding citrate in mammalian metabolism is FALSE?

A) It activates fatty acid synthesis.
B) It activates the pyruvate dehydrogenase complex.
C) It inhibits glycolysis at the step catalyzed by phosphofructokinase.
D) It is a source of acetyl-CoA for fatty acid synthesis.
E) It may be used in the Krebs cycle for production of energy.

Question 77

Blood glucose levels can not be increased by muscle glycogen degradation because muscle lacks

A) phosphorylase.
B) phosphoglucomutase.
C) hexokinase.
D) aldolase.
E) glucose 6-phosphatase.

Question 78

Which of the following would you expect to see in a fasting patient who was deficient in glucose -6-phosphatase?

A) hyperglycemia (high blood glucose)
B) normal blood sugar levels
C) increased release of glucose by the liver
D) hypoglycemia (low blood glucose)
E) increased gluconeogenesis

Question 79

Compared to metabolic activity during the daytime, when three meals are eaten, an overnight fast should cause all of the following EXCEPT

A) an increased rate of glycogenolysis.
B) increased activity of phosphoenolpyruvate carboxykinase.
C) increased rates of protein synthesis.
D) decreased activity of acetyl-CoA carboxylase.
E) increased activity of pyruvate carboxylase.

Question 80

Acetyl-CoA has been found to undergo all of the following reactions EXCEPT which one?

A) Condensation with acetoacetyl-CoA to form beta-hydroxy-beta-methyl glutaryl-CoA.
B) The ATP dependent fixation of carbon dioxide to form malonyl-CoA.
C) The NAD dependent fixation of carbon dioxide to form pyruvate and free CoA.
D) The reversible transfer of the acetyl group to acyl carrier protein (ACP) to form acetyl-ACP.
E) Condensation with glyoxylate to form malate and free CoA in plants.