Deck 18: Glycolysis

Question 1

All are characteristic of fructose bisphosphate aldolase in animal tissues EXCEPT:

A) It belongs to the lyase class of enzymes.
B) The reaction is reversible in erythrocytes (ΔG is very small).
C) It is a Class II aldolase.
D) The mechanism involves formation of a Schiff base with an active-site lysine side-chain.
E) The products are an aldotriose phosphate and a ketotriose phosphate.

Answer 1

C

Question 2

Glucokinase has a K_m value of 10.0 mM, whereas hexokinase has a K_m value of 0.1 mM. This is consistent with which of the following?

A) glucokinase acts on glucose at low concentrations.
B) glucokinase acts on glucose only at high glucose concentrations.
C) glucokinase phosphorylates most of the glucose at low glucose levels.
D) hexokinase acts on glucose only at high levels of glucose.
E) hexokinase acts at about half-maximal velocity at glucose concentrations of 4-5 mM.

Answer 2

B

Question 3

All are characteristics of Type 1 diabetes mellitus EXCEPT:

A) low levels of glucokinase.
B) glucokinase is induced.
C) insufficient insulin is produced.
D) production of little liver glycogen.
E) all are true.

Answer 3

B

Question 4

Dihydroxyacetone phosphate is:

A) an aldotriose.
B) an enantiomer of glyceraldehyde-3-phosphate.
C) derived from C4-C6 of fructose-1,6-bisphosphate.
D) isomerized to glyceraldehyde-3-phosphate by triose phosphate isomerase (TPI).
E) the least abundant component of the TPI reaction at equilibrium.

Question 5

Adenylate kinase catalyzes the reaction:
ADP + ____ ⇔ ____ + AMP

A) AMP; P_i
B) ADP; ADP
C) ADP; ATP
D) ATP; ADP
E) AMP; ATP

Question 6

The step that commits glucose to glycolysis is catalyzed by:

A) hexokinase.
B) pyruvate kinase
C) phosphofructokinase-1 (PFK-1).
D) glucokinase.
E) phosphofructokinase-2 (PFK-2)

Question 7

When phosphoglucoisomerase is secreted by T-cells it:

A) phosphorylates galactose.
B) isomerizes galactose-6-phosphate to glucose-6-phosphate.
C) promotes the survival of certain spinal neurons and sensory nerves.
D) glycosylates sphingolipids surrounding nerves.
E) none of the above.

Question 8

For phosphofructokinase-1:

A) Low ATP stimulates the enzyme, but fructose-2,6-bisphosphate inhibits
B) High ATP stimulates the enzyme, and fructose-2,6-bisphosphate activates
C) High ATP stimulates the enzyme, but fructose-2,6-bisphosphate inhibits
D) Low ATP stimulates the enzyme, and fructose-2,6-bisphosphate activates
E) ATP and fructose-2,6-bisphosphate both inhibit the enzyme

Question 9

All are characteristic of the conversion of glucose to lactate EXCEPT:

A) anaerobic pathway with no net oxidation.
B) "primed" by ATP phosphorylation.
C) located in the cytosol.
D) approximately 50% efficient in erythrocytes.
E) net production of four ATP per glucose.

Question 10

α-D-Glucose + ATP → ____ + ____ + H⁺

A) α-D-fructose; ADP
B) α-D-glucose-1-phosphate; AMP
C) α-D-glucose-1-phosphate; ADP
D) α-D-glucose-6-phosphate; ADP
E) D-glucose-1,6-bisphosphate; AMP

Question 11

All are important reasons to phosphorylate glucose in the first step of glycolysis EXCEPT:

A) the large positive free energy is important in getting the pathway started.
B) glucose-6-phosphate has a negative charge preventing transport out of the cell.
C) the concentration of free glucose in the cell is lowered favoring influx of glucose.
D) phosphorylation keeps the glucose in the cell.
E) regulatory control can be imposed only at a reaction not at equilibrium.

Question 12

All are allosteric regulators of phosphofructokinase-1 EXCEPT:

A) glucose-6-phosphate by inhibition.
B) ATP by inhibition.
C) AMP by stimulation.
D) citrate by inhibition.
E) β-D-fructose-2,6-bisphosphate by stimulation.

Question 13

All of the following characterize phosphofructokinase-1 (PFK-1) EXCEPT:

A) the most important regulatory site in glycolysis.
B) ATP increases the affinity of the enzyme for fructose-6-phosphate.
C) PFK-1 activity is a function of the energy charge of the cell.
D) AMP decreases the K_m of PFK-1 for fructose-6-phosphate.
E) the subunits of PFK-1 behave cooperatively.

Question 14

All are characteristics of the phosphofructokinase-1 catalyzed reaction EXCEPT:

A) exergonic.
B) "priming reaction".
C) "valve" controlling the rate of glycolysis.
D) commits the cell to metabolize glucose.
E) all are true.

Question 15

Class I aldolases are characterized by:

A) an endiol intermediate.
B) a requirement for biotin.
C) a Schiff base intermediate.
D) inhibition by EDTA due to a metal ion requirement.
E) coenzyme requirement for thiamin pyrophosphate (TPP).

Question 16

All are true for the isomerase reaction of glucose-6-phosphate to fructose-6-phosphate EXCEPT:

A) Mg²⁺ is required for activity.
B) it is an aldose to ketose isomerization.
C) "moving" the carbonyl from C-1 to C-2 creates a new primary alcohol group at C-1.
D) the reaction is irreversible with a large negative ΔG.
E) the enzyme belongs to the isomerase class of enzymes.

Question 17

Which of the following pathways is NOT properly paired with its precursor?

A) glycogen synthesis: glucose-1-phosphate
B) pentose phosphate pathway: glucose-6-phosphate
C) glucosamine-6-phosphate: glucose-6-phosphate
D) glucuronic acid: glucose-6-phosphate
E) all are correctly paired

Question 18

All of the following are characteristic of the coupling between glycolysis and the citric acid cycle EXCEPT:

A) glycolysis feeds acetyl CoA, via pyruvate, to the citric acid cycle.
B) citrate inhibits glucokinase to regulate glycolysis.
C) citrate builds up when citric acid cycle reaches saturation.
D) citric acid cycle directs electrons into electron transport chain for the purpose of ATP production.
E) ATP production via citric acid cycle, electron transport, and oxidative phosphorylation inhibits glycolysis.

Question 19

For the first five steps of glycolysis, the appropriate sequence of enzymes is:
A)phosphofructokinase-1 (PFK-1).
B)hexokinase / glucokinasE.C.fructose bisphosphate aldolasE.D.PhosphoglucoisomerasE.E.triose phosphate isomerase (TPI).

A) A, C, B, E, D
B) B, C, D, E, A
C) B, D, C, A, E
D) D, B, A, C, E
E) B, D, E, C, A

Question 20

Hexokinase and glucokinase belong to the kinase subclass of what class of enzymes?

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

Question 21

All are allosteric effectors of pyruvate kinase EXCEPT:

A) pyruvate.
B) AMP.
C) ATP.
D) acetyl-CoA.
E) fructose-1,6-bisphosphate.

Question 22

All are true for 2,3-bisphosphoglycerate (2,3-BPG) EXCEPT:

A) erythrocytes typically have high levels of 2,3-BPG.
B) 2,3-BPG is synthesized from 1,3-BPG.
C) a kinase converts 2,3-BPG to 3-phosphoglycerate.
D) 2,3-BPG is involved in unloading oxygen from hemoglobin.
E) bisphosphoglycerate mutase is an isomerase.

Question 23

Which of the following has the most highly exergonic hydrolysis (considering that only the highest energy bond is hydrolyzed)?

A) phosphoenolpyruvate
B) fructose-6-phosphate
C) 1,3-bisphoshpoglycerate
D) 2,3-bisphoshpoglycerate
E) fructose-1,6-bisphosphate

Question 24

The high free energy change for the conversion of PEP to pyruvate is due largely to the ____ conversion of the relatively unstable ____ tautomer of pyruvate to the more stable ____ form following the phosphoryl group transfer step.

A) unfavorable; enol; keto
B) unfavorable; keto; aldol
C) favorable; keto; enol
D) favorable; enol; keto
E) favorable; enol; aldol

Question 25

All of the following enzymes of glycolysis are allosterically regulated EXCEPT:

A) phosphofructokinase-1.
B) glyceraldehyde-3-phosphate dehydrogenase.
C) hexokinase.
D) pyruvate kinase.
E) none of the above.

Question 26

The reaction mechanism for glyceraldehyde-3-phosphate dehydrogenase involves ____ attack by a cysteine -SH group on the ____ carbon of the substrate to form a hemithioacetal.

A) electrophilic; carbonyl
B) electrophilic; acidic
C) nucleophilic; amino
D) nucleophilic; carbonyl
E) S_N2 ; amino

Question 27

Substrate-level phosphorylation occurs in glycolysis in the reaction catalyzed by ____ and belongs to ____ class of enzymes.

A) phosphoglycerate kinase; transferase
B) hexokinase; transferase
C) phosphofructokinase; transferase
D) glucokinase; transferase
E) glyceraldehyde-3-phosphate dehydrogenase; oxidoreductase

Question 28

The first intermediate of glycolysis with free energy of hydrolysis more negative than that of ATP is:

A) glucose-6-phosphate.
B) fructose-6-phosphate.
C) fructose-1,6-bisphosphate.
D) dihydroxyacetone phosphate.
E) 1,3-bisphosphoglycerate.

Question 29

In the second half of the glycolytic pathway, ____ ATP molecules are produced and with the offset of ____ ATPs consumed in the first half, the net yield is ____ ATPs per glucose.

A) four; four; zero
B) four; two; two
C) two; two; four
D) two; one; one
E) four; one; three

Question 30

The reaction, 1,3-bisphosphoglycerate → 2,3-bisphosphoglycerate, is catalyzed by:

A) bisphosphoglycerate phosphatase.
B) bisphosphoglycerate mutase.
C) 2,3-bisphosphoglycerate synthetases.
D) 3-phosphoglycerate isomerase.
E) 1,3-bisphosphoglycerate hydrolase.

Question 31

Which of the following enzymes catalyzes a reversible reaction that is an equilibrium controlled step of glycolysis?

A) phosphofructokinase-1
B) aldolase
C) pyruvate kinase
D) glucokinase
E) none of the above

Question 32

A mutase catalyzes which of the reactions, and belongs to which class of enzymes?

A) 2-phosphoglycerate ⇔ phosphoenolpyruvate + H₂O; lyase
B) pyruvate + NADH + H⁺ ⇔ lactate + NAD⁺; oxidoreductase
C) 3-phosphoglycerate ⇔ 2-phosphoglycerate; isomerase
D) dihydroxyacetone phosphate ⇔ glyceraldehyde-3-phosphate; isomerase
E) glucose-6-phosphate ⇔ fructose-6-phosphate; isomerase

Question 33

The mechanism of triose phosphate isomerase is very similar in function to:

A) hexokinase.
B) phosphoglucoisomerase.
C) phosphofructokinase.
D) fructose-1,6-bisphosphate aldolase.
E) none of the above.

Question 34

Addition of water across a double bond, or removal of water to form a double bond, is catalyzed by a subclass of the lyase class of enzymes. Which of these enzymes would be a lyase?

A) glyceraldehyde-3-phosphate dehydrogenase
B) triose phosphate isomerase (TPI)
C) phosphoglycerate mutase
D) hexokinase
E) enolase

Question 35

NADH, ____ and ____ are products of glycolysis, and the NADH must be recycled to ____ before it becomes limiting in glycolysis.

A) ATP; pyruvate; NAD⁺
B) NAD⁺; ATP; pyruvate
C) ATP; NAD⁺; ATP
D) ATP; pyruvate; lactate
E) None are true

Question 36

Glyceraldehyde-3-phosphate dehydrogenase belongs to what class of enzymes?

A) oxidoreductases
B) isomerases
C) transferases
D) hydrolases
E) ligases

Question 37

The most common form of hemolytic anemia can be the result of a genetic defect in:

A) hexokinase.
B) PFK-1.
C) pyruvate kinase
D) phosphoglycerate mutase.
E) TPI.

Question 38

PEP and 2-PG have similar amounts of potential metabolic energy with respect to decomposition to P_i, CO₂ and H₂O, but the enolase reaction:

A) creates a much more unstable reactive intermediate.
B) rearranges 2-PG into a form from which more potential energy can be released by hydrolysis.
C) rearranges 2-PG to a form with greater binding potential to the enzyme.
D) changes the ΔG of the reaction to increase the potential energy.
E) none are true.

Question 39

Which of the following amino acids provides the nucleophile in the reaction of class I aldolase?

A) Lys
B) Cys
C) Ser
D) Glu
E) His

Question 40

Hormones such as glucagon ____ glycolysis by activating cAMP-dependent protein kinase that will ____ pyruvate kinase to ____ the enzyme.

A) activate; carboxylate; activate
B) activate; phosphorylate; activate
C) activate; phosphorylate; inhibit
D) inhibit; phosphorylate; inhibit
E) inhibit; phosphorylate; activate

Question 41

If glucose was labeled with ¹⁴C at carbon #6, what carbon of pyruvate would have the ¹⁴C?

A) carboxyl carbon
B) ketone carbon
C) methyl carbon
D) the ¹⁴C would be lost as CO₂
E) the ¹⁴C could be present at any of the carbons of pyruvate

Question 42

Which of the following enzymes is correctly paired with an activator?

A) hexokinase: ATP
B) phosphofructokinase-1: fructose-2,6-bisphosphate
C) pyruvate kinase: ADP
D) glyceraldehyde-3-phosphate dehydrogenase: NAD⁺
E) glucokinase: glucose

Question 43

Lactate produced by anaerobic muscle tissue is:

A) stored in muscle until oxygen is available.
B) carried by the blood to the liver for gluconeogenesis and converted to glucose.
C) further reduced to glycerol in muscle.
D) transferred to erythrocytes to release oxygen from hemoglobin.
E) none of the above.

Question 44

Which of the following enzymes is correctly paired with an inhibitor?

A) hexokinase: ATP
B) phosphofructokinase-1: AMP
C) pyruvate kinase: ATP
D) phosphofructokinase-2: citrate
E) glyceraldehyde-3-phosphate dehydrogenase: 1,3-bisphosphoglycerate

Question 45

UDP-galactose is converted to UDP-glucose by the enzyme:

A) galactokinase.
B) galactose-uridylyltransferase.
C) Phosphoglucomutase.
D) UDP-glucose-4-epimerase.
E) UDP-galactose-2-epimerase.

Question 46

In the liver, ____ is used to phosphorylate fructose to ____.

A) phosphofructokinase-1; fructose-6-phosphate
B) phosphofructokinase-1; fructose-1-phosphate
C) fructokinase; fructose-6-phosphate
D) fructokinase; fructose-1-phosphate
E) hexokinase; fructose-1-phosphate

Question 47

Galactosemic individuals can be treated by ____ and the abnormality may disappear in adults due to metabolism of galactose-1-phosphate by:

A) medication; UDP-glucose pyrophosphorylase.
B) medication; UDP-glucose-4-epimerase.
C) restrictive diet; phosphoglucomutase.
D) restrictive diet; UDP-glucose pyrophosphorylase.
E) all of the above.

Question 48

Which of the following enzymes is NOT used when fructose is metabolized to pyruvate in the liver?

A) triose phosphate isomerase
B) glyceraldehyde-3-phospate dehydrogenase
C) glucokinase
D) phosphofructokinase-1
E) pyruvate kinase

Question 49

Under anaerobic conditions, skeletal muscle generates lactate from pyruvate to:

A) lower the pH.
B) promote release of oxygen from hemoglobin.
C) generate additional ATP.
D) be warning of muscle fatigue.
E) regenerate NAD⁺ for further glycolysis.

Question 50

The oxidation of one mole of glucose by anaerobic glycolysis yields a net of:

A) two moles of lactate and two moles of ATP.
B) two moles of lactate, two moles of NADH, and two moles of ATP.
C) two moles of lactate and six moles of ATP.
D) two moles of pyruvate and two moles of ATP.
E) two moles of pyruvate, two moles of NADH, and four moles of ATP.

Question 51

Fructose in the diet or fructose from sucrose in the diet can be a source of calories for fat synthesis in the liver because:

A) ketoses are fattening
B) fructose enters glycolysis after the primary regulation point, PFK-1
C) fructose provides a net of four ATP from glycolysis
D) fructose enters the branch of glycolysis that forms fat
E) glycerol (the "backbone" of triacylglycerols) comes specifically from fructose

Question 52

Lactose intolerance is a deficiency of the enzyme ____ that results in the metabolism of lactose by ____.

A) lactose synthase; intestinal enzymes
B) lactase; intestinal bacteria
C) lactase; intestinal viruses
D) β-galactosidase; α-amylase
E) none of the above

Question 53

The rare hereditary galactosemia involves defects in:

A) galactokinase.
B) galactose-1-phosphate uridylyltransferase.
C) phosphoglucomutase.
D) UDP-glucose-4-epimerase.
E) UDP-glucose pyrophosphorylase.

Question 54

Glycerol from hydrolysis of triacylglycerols enters glycolysis at:

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

Question 55

In alcohol fermentation from glucose, the two oxidation-reduction reactions are catalyzed by:

A) glyceraldehyde-3-phosphate dehydrogenase and alcohol dehydrogenase
B) glyceraldehyde-3-phosphate dehydrogenase and pyruvate decarboxylase
C) alcohol dehydrogenase and pyruvate decarboxylase
D) lactate dehydrogenase and pyruvate decarboxylase
E) glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase

Question 56

Lactose synthase is a dimeric complex of:

A) lactose and β-galactosidase.
B) galactosyl transferase and lactase.
C) α-lactalbumin and galactosyl transferase.
D) galactosyl transferase and β-galactosidase.
E) α-lactalbumin and β-galactosidase.

Question 57

AMP is often used in the cytosol as an indicator of low cellular energy. Which of the following enzymes would be activated by AMP?

A) hexokinase
B) phosphoglycerate kinase
C) phosphofructokinase-1
D) glyceraldehyde-3-phosphate dehydrogenase
E) both A and C are correct

Question 58

Which of the following statements is correct regarding sugar metabolism?

A) lactase, a β-galactosidase type enzyme, cleaves the β(1,4) glycosidic bond observed in lactose
B) in the liver, fructose is converted to fructose-1-P, then to dihydroxyacetone and glyceraldehyde-3-phosphate, thus skipping normal glycolytic regulation
C) in the muscle, fructose is converted into fructose-1-P by hexokinase
D) galactose enters glycolysis as galactose-6-P since the stereochemistry at C-4 is not critical for the first few enzymes of glycolysis
E) None of the above are correct

Question 59

Seven of the ten reactions of glycolysis are reversible (ΔG near zero) and can be used in reverse of glycolysis for gluconeogenesis. The three irreversible reactions are catalyzed by:

A) hexokinase, phosphoglycerate kinase, pyruvate kinase.
B) triose phosphate isomerase, phosphoglycerate mutase, pyruvate kinase.
C) enolase, phosphoglycerate kinase, phosphofructokinase-1.
D) hexokinase, phosphoglucoisomerase, glyceraldehyde-3-phosphate dehydrogenase.
E) hexokinase, phosphofructokinase-1, pyruvate kinase.

Question 60

If yeast cells were given glucose that was labeled with ¹⁴C at carbon 3, where would the ¹⁴C by found after glycolysis under anaerobic conditions?

A) CO₂
B) Ethanol, C1
C) Ethanol, C2
D) Lactic acid, C1
E) Lactic acid, C3

Question 61

Discuss the fate of pyruvate.​

Question 62

Discuss the regulation of pyruvate kinase.​

Question 63

Discuss the catabolism of fructose in the liver during the glycolytic pathway.​

Question 64

Which of the following enzymes is inhibited by phosphorylation?

A) hexokinase
B) glucokinase
C) phosphofructokinase-1
D) phosphoglycerate kinase
E) pyruvate kinase

Question 65

Which of the following enzymes has two different binding sites for ATP, one a regulatory site and the other a substrate site?

A) hexokinase
B) glucokinase
C) phosphofructokinase-1
D) phosphoglycerate kinase
E) pyruvate kinase

Question 66

Compare the G values of different steps of the glycolytic pathway and the consequences of the inhibition of these steps.​

Question 67

Explain the reaction catalyzed by triose phosphate isomerase in the first phase of gylcolysis.​