Deck 14: Glycolysis, gluconeogenesis, and the Pentose Phosphate Pathway

Question 1

Which of the following reactions in glycolysis utilizes a covalent enzyme intermediate?

A)Phosphofructokinase-1
B)Glyceraldehyde-3-phosphate dehydrogenase
C)Phosphohexose isomerase
D)Enolase
E)Triose phosphate isomerase

Answer 1

Glyceraldehyde-3-phosphate dehydrogenase

Question 2

In the phosphoglycerate mutase reaction,the side chain of which amino acid in the enzyme is transiently phosphorylated as part of the reaction?

A)Serine
B)Threonine
C)Tyrosine
D)Histidine
E)Arginine

Answer 2

Histidine

Question 3

Which of the following reactions in glycolysis utilizes a covalent enzyme intermediate?

A)Phosphofructokinase-1
B)Hexokinase
C)Phosphohexose isomerase
D)Aldolase
E)Triose phosphate isomerase

Answer 3

Aldolase

Question 4

If glucose labeled with ¹⁴C at C-2 were metabolized in the liver,the first radioactive pyruvate formed would be labeled in:

A)all three carbons.
B)both A and C.
C)its carbonyl carbon.
D)its carboxyl carbon.
E)its methyl carbon.

Question 5

The conversion of 1 mol of fructose 1,6-bisphosphate to 2 mol of pyruvate by the glycolytic pathway results in a net formation of:

A)1 mol of NAD⁺ and 2 mol of ATP.
B)1 mol of NADH and 1 mol of ATP.
C)2 mol of NAD⁺ and 4 mol of ATP.
D)2 mol of NADH and 2 mol of ATP.
E)2 mol of NADH and 4 mol of ATP.

Question 6

Which of the following is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

A)ATP
B)Cu²⁺
C)heme
D)NAD⁺
E)NADP⁺

Question 7

Inorganic fluoride inhibits enolase.In an anaerobic system that is metabolizing glucose as a substrate,which of the following compounds would you expect to increase in concentration following the addition of fluoride?

A)2-Phosphoglycerate
B)Glucose
C)Glyoxylate
D)Phosphoenolpyruvate
E)Pyruvate

Question 8

Which of the following reactions in glycolysis requires ATP as a substrate?

A)Hexokinase
B)Glyceraldehyde-3-phosphate dehydrogenase
C)Pyruvate kinase
D)Aldolase
E)Phosphoglycerate kinase

Question 9

The first reaction in glycolysis that results in the formation of an energy-rich compound is catalyzed by:

A)glyceraldehyde 3-phosphate dehydrogenase.
B)hexokinase.
C)phosphofructokinase-1.
D)phosphoglycerate kinase.
E)triose phosphate isomerase.

Question 10

Glycolysis is the name given to a metabolic pathway occurring in many different cell types.It consists of 11 enzymatic steps that convert glucose to lactic acid.Glycolysis is an example of:

A)aerobic metabolism.
B)anabolic metabolism.
C)a net reductive process.
D)fermentation.
E)oxidative phosphorylation.

Question 11

The steps of glycolysis between glyceraldehyde 3-phosphate and 3-phosphoglycerate involve all of the following except:

A)ATP synthesis.
B)catalysis by phosphoglycerate kinase.
C)oxidation of NADH to NAD⁺.
D)the formation of 1,3-bisphosphoglycerate.
E)utilization of P_i.

Question 12

Which of the following reactions in glycolysis produces ATP as a product?

A)Hexokinase
B)Glyceraldehyde-3-phosphate dehydrogenase
C)Pyruvate kinase
D)Aldolase
E)Phosphofructokinase-1

Question 13

Which of the following reactions in glycolysis is a ketose to aldose isomerization?

A)Hexokinase
B)Phosphoglycerate mutase
C)Enolase
D)Aldolase
E)Triose phosphate isomerase

Question 14

When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase,the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate.Which one of the following statements is most nearly correct,when applied to the reaction below (R = 8.315 J/mol·K and T = 298 K)?
Glucose 6-phosphate ↔ fructose 6-phosphate

A)( $\Delta$ G'° is +1.7 kJ/mol.)
B)( $\Delta$ G'° is -1.7 kJ/mol.)
C)( $\Delta$ G'° is incalculably large and negative.)
D)( $\Delta$ G'° is incalculably large and positive.)
E)( $\Delta$ G'° is zero.)

Question 15

Glycogen is converted to monosaccharide units by:

A)glucokinase.
B)glucose-6-phosphatase
C)glycogen phosphorylase.
D)glycogen synthase.
E)glycogenase.

Question 16

In glycolysis,fructose 1,6-bisphosphate is converted to two products with a standard free-energy change ( $\Delta$ G'°)of 23.8 kJ/mol.Under what conditions (encountered in a normal cell)will the free-energy change ( $\Delta$ G)be negative,enabling the reaction to proceed to the right?

A)If the concentrations of the two products are high relative to that of fructose 1,6-bisphosphate.
B)The reaction will not go to the right spontaneously under any conditions because the $\Delta$ G'° is positive.
C)Under standard conditions,enough energy is released to drive the reaction to the right.
D)When there is a high concentration of fructose 1,6-bisphosphate relative to the concentration of products.
E)When there is a high concentration of products relative to the concentration of fructose 1,6-bisphosphate.

Question 17

Glucose labeled with ¹⁴C in C-1 and C-6 gives rise in glycolysis to pyruvate labeled in:

A)A and C.
B)all three carbons.
C)its carbonyl carbon.
D)its carboxyl carbon.
E)its methyl carbon.

Question 18

The compound [¹⁸F]2-fluoro-2-deoxyglucose is:

A)an intermediate in glycolysis
B)a positive regulator of glycolysis
C)a potent anti-cancer agent
D)an antibiotic
E)an imaging agent used to detect tumors

Question 19

Which of the following reactions in glycolysis is an aldose to ketose isomerization?

A)Enolase
B)Phosphoglycerate mutase
C)Phosphohexose isomerase
D)Aldolase
E)Glyceraldehyde-3-phosphate dehydrogenase

Question 20

Galactosemia is a genetic error of metabolism associated with:

A)deficiency of galactokinase.
B)deficiency of UDP-glucose.
C)deficiency of UDP-glucose: galactose 1-phosphate uridylyltransferase.
D)excessive ingestion of galactose.
E)inability to digest lactose.

Question 21

Which one of the following statements about gluconeogenesis is false?

A)For starting materials,it can use carbon skeletons derived from certain amino acids.
B)It consists entirely of the reactions of glycolysis,operating in the reverse direction.
C)It employs the enzyme glucose 6-phosphatase.
D)It is one of the ways that mammals maintain normal blood glucose levels between meals.
E)It requires metabolic energy (ATP or GTP).

Question 22

In humans,gluconeogenesis:

A)can result in the conversion of protein into blood glucose.
B)helps to reduce blood glucose after a carbohydrate-rich meal.
C)is activated by the hormone insulin
D)is essential in the conversion of fatty acids to glucose.
E)requires the enzyme hexokinase.

Question 23

In an anaerobic muscle preparation,lactate formed from glucose labeled in C-3 and C-4 would be labeled in:

A)all three carbon atoms.
B)only the carbon atom carrying the OH.
C)only the carboxyl carbon atom.
D)only the methyl carbon atom.
E)the methyl and carboxyl carbon atoms.

Question 24

Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver?

A)Alanine
B)Glutamate
C)Palmitate
D)Pyruvate
E)( $\alpha$ -ketoglutarate)

Question 25

Which of the following statements about the pentose phosphate pathway is correct?

A)It generates 36 mol of ATP per mole of glucose consumed.
B)It generates 6 moles of CO₂ for each mole of glucose consumed
C)It is a reductive pathway;it consumes NADH.
D)It is present in plants,but not in animals.
E)It provides precursors for the synthesis of nucleotides.

Question 26

During strenuous exercise,the NADH formed in the glyceraldehyde 3-phosphate dehydrogenase reaction in skeletal muscle must be reoxidized to NAD⁺ if glycolysis is to continue.The most important reaction involved in the reoxidation of NADH is:

A)dihydroxyacetone phosphate $\rightarrow$ glycerol 3-phosphate.
B)glucose 6-phosphate $\rightarrow$ fructose 6-phosphate.
C)isocitrate $\rightarrow$ $\alpha$ -ketoglutarate.
D)oxaloacetate $\rightarrow$ malate.
E)pyruvate $\rightarrow$ lactate.

Question 27

The ultimate electron acceptor in the fermentation of glucose to ethanol is:

A)acetaldehyde.
B)acetate.
C)ethanol.
D)NAD⁺.
E)pyruvate.

Question 28

Which of the following compounds cannot serve as the starting material for the synthesis of glucose via gluconeogenesis?

A)acetate
B)glycerol
C)lactate
D)oxaloacetate
E)( $\alpha$ -ketoglutarate)

Question 29

Which of the following statements is not true concerning glycolysis in anaerobic muscle?

A)Fructose 1,6-bisphosphatase is one of the enzymes of the pathway.
B)It is an endergonic process.
C)It results in net synthesis of ATP.
D)It results in synthesis of NADH.
E)Its rate is slowed by a high [ATP]/[ADP] ratio.

Question 30

When a muscle is stimulated to contract aerobically,less lactic acid is formed than when it contracts anaerobically because:

A)glycolysis does not occur to significant extent under aerobic conditions.
B)muscle is metabolically less active under aerobic than anaerobic conditions.
C)the lactic acid generated is rapidly incorporated into lipids under aerobic conditions.
D)under aerobic conditions in muscle,the major energy-yielding pathway is the pentose phosphate pathway,which does not produce lactate.
E)under aerobic conditions most of the pyruvate generated as a result of glycolysis is oxidized by the citric acid cycle rather than reduced to lactate.

Question 31

The metabolic function of the pentose phosphate pathway is to:

A)act as a source of ADP biosynthesis.
B)generate NADPH and pentoses for the biosynthesis of fatty acids and nucleic acids.
C)participate in oxidation-reduction reactions during the formation of H₂O.
D)provide intermediates for the citric acid cycle.
E)synthesize phosphorus pentoxide.

Question 32

In comparison with the resting state,actively contracting human muscle tissue has a:

A)higher concentration of ATP.
B)higher rate of lactate formation.
C)lower consumption of glucose.
D)lower rate of consumption of oxygen
E)lower ratio of NADH to NAD⁺.

Question 33

The anaerobic conversion of 1 mol of glucose to 2 mol of lactate by fermentation is accompanied by a net gain of:

A)1 mol of ATP.
B)1 mol of NADH.
C)2 mol of ATP.
D)2 mol of NADH.
E)None of the above

Question 34

In an anaerobic muscle preparation,lactate formed from glucose labeled in C-2 would be labeled in:

A)all three carbon atoms.
B)only the carbon atom carrying the OH.
C)only the carboxyl carbon atom.
D)only the methyl carbon atom.
E)the methyl and carboxyl carbon atoms.

Question 35

All of the following enzymes involved in the flow of carbon from glucose to lactate (glycolysis)are also involved in the reversal of this flow (gluconeogenesis)except:

A)3-phosphoglycerate kinase.
B)aldolase.
C)enolase.
D)phosphofructokinase-1.
E)phosphoglucoisomerase.

Question 36

An enzyme used in both glycolysis and gluconeogenesis is:

A)3-phosphoglycerate kinase.
B)glucose 6-phosphatase.
C)hexokinase.
D)phosphofructokinase-1.
E)pyruvate kinase.

Question 37

Which of these cofactors participates directly in most of the oxidation-reduction reactions in the fermentation of glucose to lactate?

A)ADP
B)ATP
C)FAD/FADH₂
D)Glyceraldehyde 3-phosphate
E)NAD⁺/NADH

Question 38

In the alcoholic fermentation of glucose by yeast,thiamine pyrophosphate is a coenzyme required by:

A)aldolase.
B)hexokinase.
C)lactate dehydrogenase.
D)pyruvate decarboxylase.
E)transaldolase.

Question 39

Which of the following statements is incorrect?

A)Aerobically,oxidative decarboxylation of pyruvate forms acetate that enters the citric acid cycle.
B)In anaerobic muscle,pyruvate is converted to lactate.
C)In yeast growing anaerobically,pyruvate is converted to ethanol.
D)Reduction of pyruvate to lactate regenerates a cofactor essential for glycolysis.
E)Under anaerobic conditions pyruvate does not form because glycolysis does not occur.

Question 40

If glucose labeled with ¹⁴C in C-1 were fed to yeast carrying out the ethanol fermentation,where would the ¹⁴C label be in the products?

A)In C-1 of ethanol and CO₂
B)In C-1 of ethanol only
C)In C-2 (methyl group)of ethanol only
D)In C-2 of ethanol and CO₂
E)In CO₂ only

Question 41

Define "fermentation" and explain,by describing relevant reactions,how it differs from glycolysis.Your explanation should include a discussion of the role of NADH in the reaction(s).

Question 42

When glucose is oxidized via glycolysis,the carbon atom that bears the phosphate in the 3-phosphoglycerate formed may have originally been either C-1 or C-6 of the original glucose.Describe this pathway in just enough detail to explain this fact.

Question 43

The conversion of glucose into glucose 6-phosphate,which must occur in the breakdown of glucose,is thermodynamically unfavorable (endergonic).How do cells overcome this problem?

Question 44

Which of the following statements about the pentose phosphate pathway is incorrect?

A)It generates CO₂ from C-1 of glucose.
B)It involves the conversion of an aldohexose to an aldopentose.
C)It is prominant in lactating mammary gland.
D)It is principally directed toward the generation of NADPH.
E)It requires the participation of molecular oxygen.

Question 45

Glucose,labeled with ¹⁴C in different carbon atoms,is added to a crude extract of a tissue rich in the enzymes of the pentose phosphate pathway.The most rapid production of ¹⁴CO₂ will occur when the glucose is labeled in:

A)C-1.
B)C-3.
C)C-4.
D)C-5.
E)C-6.

Question 46

In a tissue that metabolizes glucose via the pentose phosphate pathway,C-1 of glucose would be expected to end up principally in:

A)carbon dioxide.
B)glycogen.
C)phosphoglycerate.
D)pyruvate.
E)ribulose 5-phosphate.

Question 47

What are the two reactions in glycolysis in which aldose to ketose isomerization is catalyzed by an enzyme? For both reactions the $\Delta$ G'° is positive.Briefly explain how the reactions are able to proceed without the input of additional energy.

Question 48

The oxidation of 3 mol of glucose by the pentose phosphate pathway may result in the production of:

A)2 mol of pentose,4 mol of NADPH,and 8 mol of CO₂.
B)3 mol of pentose,4 mol of NADPH,and 3 mol of CO₂.
C)3 mol of pentose,6 mol of NADPH,and 3 mol of CO₂.
D)4 mol of pentose,3 mol of NADPH,and 3 mol of CO₂.
E)4 mol of pentose,6 mol of NADPH,and 6 mol of CO₂.

Question 49

At which point in glycolysis do C-3 and C-4 of glucose become chemically equivalent?

Question 50

Glucose breakdown in certain mammalian and bacterial cells can occur by mechanisms other than classic glycolysis.In most of these,glucose 6-phosphate is oxidized to 6-phosphogluconate,which is then further metabolized by:

A)an aldolase-type split to form glyceric acid and glyceraldehyde 3-phosphate.
B)an aldolase-type split to form glycolic acid and erythrose 4-phosphate.
C)conversion to 1,6-bisphosphogluconate.
D)decarboxylation to produce keto- and aldopentoses.
E)oxidation to a six-carbon dicarboxylic acid.

Question 51

Show how NADH is recycled to NAD⁺ under aerobic conditions and under anaerobic conditions.Why is it important to recycle NADH produced during glycolysis to NAD⁺?

Question 52

Which of the following enzymes acts in the pentose phosphate pathway?

A)6-Phosphogluconate dehydrogenase
B)Aldolase
C)Glycogen phosphorylase
D)Phosphofructokinase-1
E)Pyruvate kinase

Question 53

There are a variety of fairly common human genetic diseases in which enzymes required for the breakdown of fructose,lactose,or sucrose are defective.However,there are very few cases of people having a genetic disease in which one of the enzymes of glycolysis is severely affected.Why do you suppose such mutations are seen so rarely?

Question 54

In the conversion of glucose to pyruvate via glycolysis,all of the following enzymes participate.Indicate the order in which they function by numbering them.
hexokinase
___ triose phosphate isomerase
___ phosphohexose isomerase
___ enolase
___ glyceraldehyde 3-phosphate dehydrogenase
___ pyruvate kinase
___ phosphofructokinase-1
Which of the enzymes represents a major regulation point in glycolysis?
Which catalyzes a reaction in which ATP is produced?
Which catalyzes a reaction in which NADH is produced?

Question 55

Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in humans,and explain the circumstances that favor each.

Question 56

In glycolysis there are two reactions that require one ATP each and two reactions that produce one ATP each.This being the case,how can fermentation of glucose to lactate lead to the net production of two ATP molecules per glucose?

Question 57

Describe the glycolytic pathway from glucose to glyceraldehyde 3-phosphate.Show structures of intermediates,enzyme names,and indicate where any cofactors participate.

Question 58

Describe the glycolytic pathway from glyceraldehyde 3-phosphate to pyruvate,showing structures of intermediates and names of enzymes.Indicate where any cofactors participate.

Question 59

Explain why P_i (inorganic phosphate)is absolutely required for glycolysis to proceed.

Question 60

All of the intermediated in the glycolytic pathway are phosphorylated.Give two plausible reasons why this might be advantageous to the cell.

Question 61

If you incubate ¹⁴C-CO₂ with liver extracts capable of performing gluconeogenesis,where does the radioactive label end up?

Question 62

Explain the biochemical basis of the human metabolic disorder called lactose intolerance.

Question 63

An extract of adipose (fat)tissue can metabolize glucose to CO₂.When glucose labeled with ¹⁴C in either C-1 or C-6 was added to the extract,¹⁴CO₂ was released with the time courses shown below.What is the major path of glucose oxidation in this extract? Explain how you reached this conclusion.

Question 64

Explain with words,diagrams,or structures why lactate accumulates in the blood during bursts of very vigorous exercise (such as a 100-meter dash).

Question 65

During strenuous activity,muscle tissue demands large quantities of ATP,compared with resting muscle.In white skeletal muscle (in contrast with red muscle),ATP is produced almost exclusively by fermentation of glucose to lactate.If a person had white muscle tissue devoid of the enzyme lactate dehydrogenase,how would this affect his or her metabolism at rest and during strenuous exercise?

Question 66

When glucose labeled with a ¹⁴C at C-1 (the aldehyde carbon)passes through glycolysis,the glyceraldehyde 3-phosphate that is produced from it still contains the radioactive carbon atom.Draw the structure of glyceraldehyde 3-phosphate,and circle the atom(s)that would be radioactive.

Question 67

The bacterium E.coli can grow in a medium in which the only carbon source is glucose.How does this organism obtain ribose 5-phosphate for the synthesis of ATP? (Do not describe ATP synthesis,just the origin of ribose 5-phosphate. )Show structures and indicate where cofactors participate.

Question 68

If brewer's yeast is mixed with pure sugar (glucose)in the absence of phosphate (P_i),no ethanol is produced.With the addition of a little P_i,ethanol production soon begins.Explain this observation in 25 words or less.

Question 69

Explain why the phosphorolysis of glycogen is more efficient than the hydrolysis of glycogen in mobilizing glucose for the glycolytic pathway.

Question 70

Draw the structure of 1,3-bisphosphoglycerate.Indicate with an arrow the phosphate ester,and circle the phosphate group for which the free energy of hydrolysis is very high.

Question 71

Rat liver is able to metabolize glucose by both the glycolytic and the pentose phosphate pathways.Indicate in the blanks if the following are properties of glycolytic (G),pentose phosphate (P),both (G + P),or neither (0):
_____ NAD⁺ is involved.
_____ CO₂ is liberated.
_____ Phosphate esters are intermediates.
_____ Glyceraldehyde 3-phosphate is an intermediate.
_____ Fructose 6-phosphate is an intermediate.

Question 72

Describe the process of glycogen breakdown in muscle.Include a description of the structure of glycogen,the nature of the breakdown reaction and the breakdown product,and the required enzyme(s).

Question 73

Describe the fate of pyruvate,formed by glycolysis in animal skeletal muscle,under two conditions: (a)at rest,and (b)during an all-out sprint.Show enough detail in your answer to explain why pyruvate metabolism is different in these two cases.

Question 74

The yeast used in brewing the alcoholic beverage beer can break down glucose either aerobically or anaerobically using alcoholic fermentation.Explain why beer is brewed under anaerobic conditions.

Question 75

What are the biological functions of the pentose phosphate pathway?

Question 76

Two reactions in glycolysis produce ATP.For each of these,show the name and structure of reactant and product,indicate which cofactors participate and where,and name the enzymes.

Question 77

In gluconeogenesis,how do animals convert pyruvate to phosphoenolpyruvate? Show structures,enzymes,and cofactors.

Question 78

What is gluconeogenesis,and what useful purposes does it serve in people?

Question 79

Yeast can metabolize D-mannose to ethanol and CO₂.In addition to the glycolytic enzymes,the only other enzyme needed is phosphomannose isomerase,which converts mannose 6-phosphate to fructose 6-phosphate.If mannose is converted to ethanol and CO₂ by the most direct pathway,which of the compounds and cofactors in this list are involved?

A)Lactate
B)Acetaldehyde
C)Acetyl-CoA
D)FAD
E)Glucose 6-phosphate
F)Fructose 1-phosphate
G)Pyruvate
H)Lipoic acid
I)Thiamine pyrophosphate
J)Dihydroxyacetone phosphate