Deck 22: Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Question 1

In the Cori cycle, the liver ____ because it has a typically high ____.

A) shares the load of exercising muscle; acetate level
B) converts lactate to lactose; galactose
C) shares the load of exercising muscle; NAD⁺/NADH ratio
D) burns fat; ATP
E) converts glucose to lactate; NAD⁺/NADH ratio

Answer 1

C

Question 2

Glucose monitoring devices use the reaction, Glucose + O₂ + H₂O → gluconate + 2 ____, which is catalyzed by the enzyme ____.

A) H₂O; glucose hydrolase
B) H₂O; glucose oxidase
C) H₂O₂; peroxidase
D) H₂O₂; glucose oxidase
E) H₂O; gluconate synthase

Answer 2

D

Question 3

The primary regulatory point of gluconeogenesis is ____.

A) glucose-6-phosphatase
B) fructose-1,6-bisphosphatase
C) fructose-2,6-bisphosphatase
D) pyruvate carboxylase
E) PEP carboxykinase

Answer 3

B

Question 4

Glucose-6-phosphatase is located in the ____ and produces ____ in vesicles that diffuse to the ____ releasing their contents into the blood stream.

A) mitochondria; lactate; cytosol
B) cytosol; glucose; plasma membrane
C) endoplasmic reticulum; glucose-6-phosphate; cytosol
D) endoplasmic reticulum; glucose; plasma membrane
E) cytosol; glucose-6-phosphate; endoplasmic reticulum

Question 5

The endoplasmic reticulum bound enzyme that hydrolyzes glucose-6-phosphate to glucose in liver is:

A) glucokinase.
B) glucose oxidase.
C) hexokinase.
D) phosphoglucomutase.
E) glucose-6-phosphatase.

Question 6

The pentose phosphate pathway is an important source of ____, and for ____, an essential precursor for ATP, NAD⁺, FAD, CoA, DNA and RNA.

A) ATP; NADH
B) NADH; NADPH
C) NADPH; ribose-5-phosphate
D) ribose-5-phosphate; ATP
E) all are true

Question 7

All of the enzymes of gluconeogenesis may be found in the cytosol EXCEPT ____ which is only found in the mitochondria.

A) PEP carboxykinase
B) pyruvate carboxylase
C) fructose-1,6-bisphosphatase
D) glucose-6-phosphatase
E) all are only in cytosol

Question 8

Which of the following is absolutely essential for the activation of pyruvate carboxylase?

A) high concentrations of acetyl-CoA
B) low levels of ATP
C) high levels of oxaloacetate
D) high levels of TCA cycle intermediates
E) high levels of citrate

Question 9

In the gluconeogenic pathway, the three regulated reactions of glycolysis catalyzed by ____, ____ and ____ are replaced by alternative reactions.

A) glucokinase; PFK-1; pyruvate kinase
B) phosphoglucoisomerase; PFK-1; pyruvate kinase
C) PFK-1; triose phosphate isomerase; pyruvate kinase
D) glucokinase; PFK-1; glyceraldehyde-3-phosphate dehydrogenase
E) glucokinase; PFK-1; pyruvate carboxylase

Question 10

The reaction sequence for the pyruvate carboxylase catalyzed reaction is:
A)formation of N-carbonyl biotin
B)attack of HCO₃− on ATP
C)liberation of P_i
D)formation of carbonylphosphate
E)C-3 carbanion of pyruvate attack on N-carbonyl biotin

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

Question 11

The major tissues carrying out gluconeogenesis are the ____ and ____.

A) brain; muscles
B) muscles; kidneys
C) liver; kidneys
D) liver; red blood cells
E) red blood cells; brain

Question 12

Gluconeogenesis is not simply reversal of glycolysis since 2 pyruvate → glucose requires the input of ____ equivalents of ATP and ____ equivalents of GTP.

A) 0; 6
B) 2; 4
C) 3; 3
D) 4; 2
E) 6; 0

Question 13

If levels of ____ and/or ____ are low, pyruvate is directed primarily into ____; but if they are high, pyruvate is converted into ____ for gluconeogenesis.

A) NADH; ATP; glycolysis; OAA
B) ATP; NADPH; glycolysis; acetyl CoA
C) ATP; acetyl CoA; TCA cycle; OAA
D) NAD⁺; acetyl CoA; TCA cycle; acetyl CoA
E) ATP; acetyl CoA; glycolysis; malate

Question 14

All are required for pyruvate carboxylase EXCEPT:

A) biotin covalently linked to the enzyme.
B) thiamin pyrophosphate (TPP).
C) ATP.
D) acetyl-CoA as an allosteric activator.
E) tetrameric enzyme in the mitochondria.

Question 15

Gluconeogenesis is the synthesis of:

A) glucose from non-carbohydrate precursors.
B) glycogen from glucose.
C) pyruvate from glucose.
D) fatty acids from glucose.
E) glucose from fatty acids.

Question 16

Pyruvate carboxylase consumes a(n) ____ to drive a carboxylation so that ____ could use the energy from decarboxylation to facilitate formation of PEP.

A) NADH; pyruvate dehydrogenase
B) NADH; lactate dehydrogenase
C) ATP; pyruvate kinase
D) ATP; PEP carboxykinase
E) GTP; nucleotide diphosphate kinase

Question 17

In the pyruvate carboxylase catalyzed reaction, bicarbonate is "activated" by attachment to the ____ of ATP to form ____.

A) β-phosphate; carbonyl ADP
B) α-phosphate; carbonyl AMP
C) α-phosphate; carbonylphosphate
D) γ-phosphate; carbonylphosphate
E) γ-phosphate; carbonyl AMP

Question 18

Which of the following enzymes is found in gluconeogenesis but not glycolysis?

A) phosphoglucoisomerase
B) glucose-6-phosphatase
C) pyruvate carboxylase
D) fructose-1,6-bisphosphatase
E) PEP carboxykinase

Question 19

All are substrates for gluconeogenesis EXCEPT:

A) glycerol.
B) lactate.
C) acetate.
D) pyruvate.
E) most amino acids.

Question 20

Which of the following reactions represents the gluconeogenic alternative to the irreversible reaction of PFK-1 in glycolysis?

A) fructose-6-P + ADP → fructose + ATP
B) fructose-6-P + H₂O → fructose + P_i
C) fructose-1,6-bisphosphate + ADP → fructose-6-P + ATP
D) fructose-1,6-bisphosphate + H₂O → fructose-6-P + P_i
E) none of the above

Question 21

Characteristics of glucose-6-phosphate dehydrogenase include all EXCEPT:

A) located in the mitochondria.
B) strongly inhibited by [NADPH].
C) inhibited by fatty acid-CoA.
D) uses NADP⁺ as a coenzyme.
E) forms a cyclic ester (lactone) of 6-phosphogluconate.

Question 22

Among the many physiological changes elicited by epinephrine, the initiation of the adenylyl cyclase cascade includes all EXCEPT:

A) activation of glycogenolysis in liver.
B) inhibition of glycogen synthase.
C) stimulation of glycolysis by 2000 fold.
D) activation of glycogenolysis in muscles.
E) all are true

Question 23

Insulin in the bloodstream is a response to increased blood glucose, and:

A) stimulates gluconeogenesis.
B) inhibits glycolysis.
C) stimulates glycogen synthesis in muscle and liver.
D) stimulates glycogen breakdown in liver.
E) inhibits phosphoprotein phosphatase-1.

Question 24

An individual with von Gierke's disease lacks the enzyme ____ which is a liver enzyme used to maintain ____. As a result, the patient is ____.

A) glycogen synthase; liver glycogen; fat
B) glycogen synthase; ATP levels; weak
C) phosphoprotein phosphatase-1; blood glucose; hypoglycemic
D) glucose-6-phosphatase; blood glucose; hypoglycemic
E) glucose-6-phosphatase; muscle glycogen; weak

Question 25

A blood test for "Glycated hemoglobin" can determine the:

A) present blood glucose concentration.
B) average glucose concentration in the blood over the past several months.
C) level of AGEs in the blood stream.
D) blood glucose concentration over this last month.
E) none are true.

Question 26

The energy input for the synthesis of glycogen occurs during which of the following enzyme catalyzed steps?

A) phosphoglucomutase
B) UDP-glucose pyrophosphorylase
C) glycogen synthase
D) amylo-(1,4→1,6)-transglycosylase
E) none of the above require energy input

Question 27

Which of the following occurs as a result of cortisol release from the adrenal gland?

A) activation of gluconeogenesis
B) increased glycogen synthesis
C) activation of the urea cycle
D) increased degradation of muscle protein
E) all of the above

Question 28

Cellular levels of fructose-2,6-bisphosphate (F-2,6-BP) are controlled by the tandem enzyme ____ and ____.

A) fructokinase; F-2,6-BPase
B) F-2,6-BPase; PFK-2
C) PFK-2; PFK-1
D) PFK-1; F-2,6-BPase
E) PFK-2; fructokinase

Question 29

____ phosphorylates and thus ____ the enzyme PFK-2 which simultaneously ____ F-2,6-BPase.

A) adenylate cyclase; activates; inhibits
B) adenylate cyclase; inhibits; activates
C) cAMP-dependent protein kinase; activates; inhibits
D) cAMP-dependent protein kinase; inhibits; activates
E) cAMP-dependent protein kinase; activates; activates

Question 30

Phosphopentose isomerase is quite similar to the reaction and mechanism of the ____ catalyzed reaction.

A) UDP-glucose epimerase
B) phosphoglycerate isomerase
C) phosphopentose epimerase
D) phosphoglucoisomerase
E) all are similar

Question 31

Limit dextrins are degraded by the action of ____ which has two distinct enzymatic activities known as ____ and ____.

A) α-amylase; β-amylase; α(1→6)glucosidase
B) debranching enzyme; oligo(α1,4→ α1,4)glucanotransferase; α(1→6)glucosidase
C) debranching enzyme; oligo(α1,4→ α1,4)glucanotransferase; α(1→6)glucosidase
D) α-amylase; oligo(α1,4→ α1,6)glucanotransferase; α(1→6)glucosidase
E) α-amylase; β-amylase; oligo(α1,4→ α1,4)glucanotransferase

Question 32

The ratio of NADP⁺/NADPH in liver runs about 1/67 which means that:

A) it is similar to the ratio of NAD⁺/NADH.
B) glucose-6-phosphate dehydrogenase will be turned on most of the time.
C) glucose-6-phosphate is rate limiting for pentose phosphate pathway.
D) glucose-6-phosphate preferentially goes to the pentose phosphate pathway.
E) glucose-6-phosphate dehydrogenase activity is dependent upon use of some of the NADPH before activity increases.

Question 33

The 6-phosphogluconate dehydrogenase reaction is an example of ____ and results in the production of ____.

A) substrate-level phosphorylation; ATP
B) oxidative-decarboxylation; NADPH
C) TPP-assisted decarboxylation; NADH
D) phosphate addition; ADP
E) none of the above

Question 34

Glycogen synthesis and degradation must be carefully controlled at ____ and ____ to properly serve the metabolic needs for the organism.

A) glucokinase; hexokinase
B) hexokinase; glycogen synthase
C) glycogen synthase; glucokinase
D) glycogen phosphorylase; glycogen synthase
E) glycogen phosphorylase; hexokinase

Question 35

All are true for α-amylase EXCEPT:

A) catalyzes hydrolysis of α (1→4) linkages in starch.
B) is an important component of saliva and pancreatic juice.
C) catalyzes hydrolysis of α (1→6) linkages in amylopectin.
D) catalyzes hydrolysis of α (1→4) linkages in glycogen.
E) activity is reduced in highly branched regions of polysaccharides and stops four residues from any branch point.

Question 36

Physiological effects of insulin include all EXCEPT:

A) stimulates glycogen synthesis
B) induces synthesis of glucokinase, PFK-1 and pyruvate kinase
C) stimulates active transport of glucose and amino acids into muscle and adipose tissues
D) stimulates fructose-1,6-bisphosphatase
E) inhibits glycogen phosphorylase

Question 37

Which of the following effectors is required for glycogen synthase activity when the enzyme is phosphorylated?

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

Question 38

The initiation of glycogen synthesis occurs by transfer of glucose from UDP-glucose to the:

A) 4-position of free glucose.
B) 2-position of fructose.
C) non-reducing end of maltose.
D) serine-OH group of glycogen synthase.
E) tyrosine-OH group of glycogenin.

Question 39

All are characteristics of AGEs EXCEPT:

A) AGEs mean advanced glycation end-products.
B) Glycated hemoglobin in a patient is an indication of blood glucose levels over the past few months.
C) AGEs generated by elevated blood glucose contribute to circulation, joint and vision problems of diabetics.
D) AGEs form by enzyme catalyzed Schiff base formation between sugars and proteins.
E) AGEs alter the function of the protein to which they are attached.

Question 40

All are physiological changes initiated by glucagon EXCEPT:

A) activation of glycogenolysis in liver.
B) stimulation of liver gluconeogenesis.
C) long-term maintenance of steady-state levels of glucose in the blood stream.
D) activation of glycogenolysis in muscles.
E) all are true.

Question 41

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

A) glucose-6-phosphate dehydrogenase
B) phosphofructokinase-1
C) glycogen synthase
D) glyceraldehyde-3-phosphate dehydrogenase
E) none of the above

Question 42

If NADPH is needed for biosynthetic reactions but ribose-5-P is not needed, which of the following best represents the net reaction of the pentose phosphate pathway?

A) 4 Fruc-6-P + 2 glyceraldehyde-3-P → 6 ribose-5-P
B) 3 Gluc-6-P + 6 NADP⁺ → 6 NADPH + 3 CO₂ + 2 Fruc-6-P + 1 glyceraldehyde-3-P
C) Gluc-6-P + 2 NADP⁺ → 2 NADPH + CO₂ + ribose-5-P
D) both b and c will occur
E) None of the above

Question 43

A transaldolase is an enzyme that catalyzes:

A) transfers of three-carbon units from a ketose to an aldose.
B) isomerization of ketoses into aldoses such as the conversion of ribulose-5-phosphate to ribose-5-phosphate.
C) epimerization of ketoses such as the conversion of xylulose-5-phosphate into ribulose-5-phosphate.
D) TPP-dependent transfer of 2-carbon units to the recipient aldose.
E) transfer of keto groups from C-2 to C-3 of a ketose.

Question 44

Which of the following results when glucagon binds to its receptor?

A) glycolysis is activated
B) protein synthesis is activated
C) the citric acid cycle is inhibited
D) glycogen synthesis is inhibited
E) gluconeogenesis is inhibited

Question 45

The transaldolase catalyzed activity is similar to what glycolytic enzyme?

A) phosphoglucomutase
B) enolase
C) glyceraldehyde-3-phosphate dehydrogenase
D) PFK-1
E) aldolase

Question 46

Explain UDP-glucose synthesis.​

Question 47

How is glucose-6-phosphate converted to glucose in the gluconeogenesis pathway?​

Question 48

Which of the following reactions is catalyzed by a transketolase in the pentose phosphate pathway?
I)
Fructose-6-P + glyceraldehyde-3-P ⇔ xylulose-5-P + erythrose-4-P
II)
Erythrose-4-P + fructose-6-P ⇔ sedoheptulose-7-P + glyceraldehyde-3-P
III)
Sedoheptulose-7-P + glyceraldehyde-3-P ⇔ ribose-5-P + xyulose-5-P

A) I only
B) II and III
C) II only
D) I and III
E) I and II

Question 49

Which of the following enzymes would be activated by phosphorylation as a result of glucagon binding to its receptor on the cell membrane?

A) pyruvate carboxylase
B) glycogen synthase
C) pyruvate kinase
D) fructose-2,6-bisphosphatase
E) none of the above

Question 50

Discuss the regulation of gluconeogenesis by acetyl-CoA.​

Question 51

Transketolase belongs to what class of enzymes?

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

Question 52

The appropriate sequence for the transketolase catalyzed reaction would be:
A)reactive enamine attack on the aldehyde group of an aldose
B)β-cleavage of Schiff base intermediate to release an aldose
C)formation of Schiff base intermediate of a new ketose
D)active site lysine forms Schiff base with keto-carbonyl group
E)Schiff base hydrated to ketose and enzyme

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

Question 53

Describe the degradation of limit dextrins that result after α-amylase acts on glycogen.​

Question 54

The polyol pathway is a suspected pathway for diabetic induced cataract formation and involves the enzyme:

A) aldose reductase.
B) glucose-6-phosphate dehydrogenase.
C) phosphopentose isomerase.
D) phosphopentose epimerase.
E) transaldolase.

Question 55

What coenzyme is found in pyruvate carboxylase that aids in many carboxylation reactions?

A) thiamine pyrophosphate
B) biotin
C) folic acid
D) lipoic acid
E) none of the above

Question 56

Which of the following can be used as a substrate for gluconeogenesis in the liver?

A) alanine
B) glutamic acid
C) glycerol
D) succinate
E) all of the above

Question 57

Which of the following pairs of enzymes would NOT be active in the liver at the same time?

A) aldolase and triose phosphate isomerase
B) fructose-1,6-bisphosphatase and phosphofructokinase-2
C) pyruvate kinase and phosphofructokinase-1
D) glycogen synthase and glucokinase
E) none of the above

Question 58

When a cell with the pentose phosphate pathway has need for more pentose phosphates, but no additional NADPH:

A) glucose-6-phosphate dehydrogenase is activated.
B) the oxidative and non-oxidative enzymes of the pentose phosphate pathway are active.
C) the non-oxidative enzymes produce pentose phosphates from fructose-6-phosphate and glyceraldehyde-3-phosphate.
D) all enzymes of glycolysis and pentose phosphate pathway are active.
E) none are true.

Question 59

Discuss the significance of the pentose phosphate pathway. What is the net reaction of the first four steps of the pathway?​

Question 60

If both NADPH and ribose-5-P are needed which of the following best represents the net reaction of the pentose phosphate pathway?

A) 4 Fruc-6-P + 2 glyceraldehyde-3-P → 6 ribose-5-P
B) 3 Gluc-6-P + 6 NADP⁺ → 6 NADPH + 3 CO₂ + 2 Fruc-6-P + 1 glyceraldehyde-3-P + 6 H⁺
C) Gluc-6-P + 2 NADP⁺ + 2 H₂O → 2 NADPH + CO₂ + ribose-5-P + 2 H⁺
D) Gluc-6-P + 12 NADP⁺ + 6 H₂O → 1 2 NADPH + 6 CO₂ + 12 H⁺ + Pi
E) None of the above