Pentose Phosphate Pathway Flashcards by Mind Med

Q

Where does the pentose phosphate pathway occur?

A

cytosol

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Q

What are the products and byproducts of the PPP?

A

5-carbon sugars (pentose)
NADPH
CO2

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Q

The following are other names of the PPP, except:

A. Hexose Monophosphate Shunt
B. Phosphoglucose Pathway
C. Warburg-Dickens Pathway
D. Direct Oxidative Pathway

A

B. Phosphoglucose Pathway

It is also known as PhosphoGLUCONATE pathway

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Q

How many molecules of G6P are initially used in the pentose phosphate pathway?

A

3

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Q

What are the products of the oxidative stage?

A

3 ribose-5-P
6 NADPH
3 CO2

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Q

For every 3 G6P, how many 5 carbon sugars are made in the non-oxidative pathway?

A

3

2 xylulose-5-P
1 ribose-5-P

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Q

For every 3 G6P, how many 6 carbon sugars are made in the non-oxidative pathway?

A

2

2 fructose-6-P

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Q

For every 3 G6P, how many 3 carbon sugars are made in the non-oxidative pathway?

A

1 GA3P

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Q

Transketolase and transaldolase reactions link PPP with which pathways?

A

Glycolysis and Gluconeogenesis

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Q

How many carbons are initially present at the start of PPP

A

18

6 carbons, 3 G6P

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Q

How many carbons are lost during PPP?

A

3 (due to release of 3 CO2)

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Q

Remnant carbons from PPP form which molecules?

A

12 carbons = 2 fructose-6-P
3 carbons = 1 GA3P

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Q

G6P DH stimulated by decreased NADPH/NADP ratio

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

B. Fasting / Low reducing power

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Q

Increased NADPH

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

A. Well fed / High reducing power

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Q

Decreased NADPH

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

B. Fasting / Low reducing power

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Q

G6P DH inhibited by increased NADPH/NADP ratio

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

A. Well fed / High reducing power

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Q

Increased NADPH synthesis

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

B. Fasting / Low reducing power

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Q

PPP diverts G6P

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

B. Fasting / Low reducing power

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Q

PPP will not divert G6P from glycolysis

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

A. Well fed / High reducing power

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Q

Decreased NADPH synthesis

A. Well fed / High reducing power
B. Fasting / Low reducing power

A

A. Well fed / High reducing power

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Q

If PPP starts with 3 G6P and 6 NADP, how many of its products are formed?

Be specific.

A

3 ribulose-5-P
6 NADPH
3 CO2

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Q

If PPP starts with 3 ribulose-5-P, how many of its products are formed?

Be specific.

A

2 xylulose-5-P
1 ribose-5-P

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Q

If PPP starts with 2 xylulose-5-P and ribose-5-P, how many of its products are formed?

Be specific.

A

2 fructose-6-P
1 GA3P

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Q

If the cell requires NADPH for reducing power, what does the PPP do?

A

Continue on the NON-OXIDATIVE PATHWAY and PRODUCE FRUCTOSE-6-P to be converted back to G6P in glycolysis (reversible) for NADPH production

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If the cell requires nucleotides and nucleic acids, what does the PPP do?

stops at the oxidative pathway as ribose-5-P and DOES NOT PROCEED TO THE NON-OXIDATIVE PATHWAY

GSH A. Reduced form of glutathione B. Oxidized form of glutathione

A. Reduced form of glutathione

GSSG A. Reduced form of glutathione B. Oxidized form of glutathione

B. Oxidized form of glutathione This needs to be converted back to GSH to become a functional antioxidant via NADPH

Which group of cysteine in glutathione is responsible for its anti-oxidant function?

Sulfhydryl group

What is the primary function of the Pentose Phosphate Pathway (PPP)? a) ATP production b) Generation of NADPH and ribose 5-phosphate c) Production of pyruvate d) Synthesis of lactate

a) ATP production

Which of the following is NOT a product of the oxidative phase of PPP? a) NADPH b) CO2 c) Ribulose 5-phosphate d) ATP

d) ATP

What is the final product of the oxidative phase? a) Glucose 6-phosphate b) Ribose 5-phosphate c) Ribulose 5-phosphate d) Fructose 6-phosphate

c) Ribulose 5-phosphate

Which enzyme catalyzes the first step and is the rate-limiting enzyme of PPP? a) Hexokinase b) Glucose 6-phosphate dehydrogenase c) Transketolase d) Phosphofructokinase

b) Glucose 6-phosphate dehydrogenase

What cofactor is essential for transketolase activity? a) NAD+ b) Thiamine Pyrophosphate (TPP) c) FAD d) Vitamin B12

b) Thiamine Pyrophosphate (TPP)

How many carbons does transketolase transfer? a) 1 b) 2 c) 3 d) 6

b) 2

How many carbons does transaldolase transfer? a) 1 b) 2 c) 3 d) 5

c) 3

Which phase of the PPP is reversible? a) Oxidative phase b) Non-oxidative phase c) Both phases d) Neither phase

b) Non-oxidative phase

What is the key allosteric inhibitor of glucose 6-phosphate dehydrogenase? a) NADH b) NADPH c) ATP d) FADH2

b) NADPH

What stimulates the oxidative phase of the PPP? a) Increase in NADPH b) Increase in glucose 6-phosphate c) Decrease in NADPH d) Decrease in glucose

c) Decrease in NADPH

What is the main regulatory mechanism for the PPP? a) ATP level b) NADPH/NADP+ ratio c) Glucose 6-phosphate concentration d) Oxygen saturation

b) NADPH/NADP+ ratio

Which pathway supplies ribose 5-phosphate without generating NADPH? a) Oxidative phase of PPP b) Non-oxidative phase of PPP c) Glycolysis d) Citric Acid Cycle

b) Non-oxidative phase of PPP

What is the distinguishing feature between glycolysis and PPP? a) Location in cell b) NAD+ usage vs NADP+ usage c) Production of ATP only d) No connection between glycolytic intermediates

b) NAD+ usage vs NADP+ usage

Which of the following describes a function of NADPH generated by PPP? a) DNA phosphorylation b) Reductive biosynthesis and antioxidant defense c) Cellular respiration d) Protein glycosylation

b) Reductive biosynthesis and antioxidant defense

Which cell type relies heavily on PPP for antioxidant defense? a) Muscle cells b) Epithelial cells c) Red blood cells d) Neurons

c) Red blood cells

What is the consequence of G6PD deficiency? a) Sickle cell anemia b) Hemolytic anemia after exposure to oxidative stress c) Hypochromic anemia d) Megaloblastic anemia

b) Hemolytic anemia after exposure to oxidative stress

Which enzyme uses ribose 5-phosphate for nucleotide synthesis? a) Ribulose 5-phosphate isomerase b) Adenylate cyclase c) Glutathione peroxidase d) Malate dehydrogenase

a) Ribulose 5-phosphate isomerase

Which molecule acts as an allosteric stimulator of PPP in times of need for NADPH? a) High NADPH b) Low NADPH c) Low ATP d) High FAD

b) Low NADPH

What is the role of glutathione in red blood cells? a) Competes with NADPH b) Reduces reactive oxygen species (ROS) c) Oxidizes DNA d) Synthesizes ribose 5-phosphate

b) Reduces reactive oxygen species (ROS)

Which phase of PPP provides glycolytic intermediates? a) Oxidative b) Non-oxidative c) Both d) Neither

b) Non-oxidative

In PPP, what is the main substrate? a) Fructose 1,6-bisphosphate b) Glucose 6-phosphate c) Sucrose d) Ribose 5-phosphate

b) Glucose 6-phosphate

Which enzyme deficiency is tested using thiamine pyrophosphate assay? a) G6PD b) Ribulose 5-phosphate isomerase c) Transketolase d) Transaldolase

c) Transketolase

Which of the following triggers hemolytic anemia in G6PD deficiency? a) Cold exposure b) Fava beans ingestion c) Exercise d) Vitamin D overdose

b) Fava beans ingestion

Which is NOT a function of NADPH in biosynthesis? a) Fatty acid synthesis b) Cholesterol synthesis c) Glycolysis d) Bile acid synthesis

c) Glycolysis

Carbon flow in PPP: how many carbons are lost as CO2 from three glucose 6-phosphate? a) 1 b) 2 c) 3 d) 6

c) 3

What is a secondary product of PPP besides NADPH? a) Pyruvate b) Ribose 5-phosphate c) Uric acid d) ATP

b) Ribose 5-phosphate

Which metabolic need drives the PPP to produce ribose 5-phosphate directly? a) DNA replication b) High demand for nucleotides c) ATP synthesis d) Electron transport

b) High demand for nucleotides

Which pathway predominantly operates in tissues synthesizing fatty acids and steroids? a) Glycolysis b) PPP nonoxidative phase c) TCA cycle d) Gluconeogenesis

b) PPP oxidative phase

What is the structure of glutathione? a) Dipeptide composed of serine and ala b) Tripeptide composed of glutamate, cysteine, and glycine c) Pentapeptide composed of proline, lysine, valine, methionine, and arginine d) Polysaccharide with amino acid side chains

b) Tripeptide composed of glutamate, cysteine, and glycine

Which phase of PPP provides NADPH used for maintaining glutathione in its reduced form? a) Non-oxidative phase b) Oxidative phase c) Both phases d) PPP does not provide NADPH

b) Oxidative phase

Which enzyme deficiency is most commonly associated with drug-induced hemolytic anemia? a) Glutathione synthetase b) Glucose-6-phosphate dehydrogenase c) Hexokinase d) Transaldolase

b) Glucose-6-phosphate dehydrogenase

What is the main consequence of G6PD deficiency in red blood cells? a) Increased ATP synthesis b) Decreased reduced glutathione c) Increased synthesis of fatty acids d) Decreased alcohol metabolism

b) Decreased reduced glutathione

Which of the following is a clinical sign of hemolytic anemia due to G6PD deficiency? a) Hemoglobinuria b) Hypoglycemia c) Hypercalcemia d) Leucocytosis

a) Hemoglobinuria

Characteristic laboratory finding in G6PD deficiency includes: a) Heinz bodies in RBCs b) Increased reticulocyte count c) Polycythemia d) Microcytosis

a) Heinz bodies in RBCs

Which biochemical pathway is compromised in G6PD deficiency? a) Glycolysis b) Pentose phosphate pathway c) Urea cycle d) Citric acid cycle

b) Pentose phosphate pathway

Wernicke-Korsakoff syndrome is associated with deficiency of which enzyme’s cofactor? a) NAD+ b) Thiamine pyrophosphate (TPP) c) FAD d) Biotin

b) Thiamine pyrophosphate (TPP)

Major signs and symptoms of Wernicke-Korsakoff syndrome include: a) Memory loss and confusion b) Hypertension and fever c) Paralysis and jaundice d) Hypernatremia and ataxia

a) Memory loss and confusion

Pathophysiology of Wernicke-Korsakoff syndrome in PPP centers on dysfunction of: a) Transaldolase b) Transketolase c) Phosphofructokinase d) Hexokinase

b) Transketolase

Treatment for Wernicke-Korsakoff syndrome involves supplementation of: a) Iron b) Thiamine c) Potassium d) Calcium

b) Thiamine

Which enzyme uses NADPH as a reducing agent for detoxification reactions? a) Cytochrome P450 monooxygenase b) Hexokinase c) Lactate dehydrogenase d) Phosphoglycerate kinase

a) Cytochrome P450 monooxygenase

NADPH is a cofactor for which enzyme involved in antioxidant protection? a) Glutathione peroxidase b) Glutathione reductase c) Transaldolase d) Pyruvate kinase

b) Glutathione reductase

Which pathway requires ribose-5-phosphate for synthesis? a) Urea cycle b) DNA and RNA synthesis c) Beta-oxidation d) Glycolysis

b) DNA and RNA synthesis

A person with G6PD deficiency should avoid all EXCEPT: a) Primaquine b) Sulfonamides c) Alcohol d) Vitamin C

d) Vitamin C

Which of the following is a function of NADPH in phagocytic cells? a) Inhibits superoxide formation b) Stimulates superoxide anion generation c) Increases lactate production d) Produces beta-globin chains

b) Stimulates superoxide anion generation

Which is the immediate precursor for NADPH synthesis in the PPP? a) Glucose b) Glucose-6-phosphate c) Pyruvate d) Fructose-1,6-bisphosphate

b) Glucose-6-phosphate

Why is the PPP especially important in red blood cells? a) They need high levels of ATP b) PPP prevents oxidative damage by supplying NADPH c) They synthesize steroids d) They perform gluconeogenesis

b) PPP prevents oxidative damage by supplying NADPH

A deficiency in transketolase’s cofactor leads to: a) Type 1 diabetes b) Slowed PPP and neurological deficits c) Increased cholesterol synthesis d) Enhanced glycolytic flux

b) Slowed PPP and neurological deficits

Which amino acid contributes the sulfhydryl group in glutathione? a) Glutamate b) Cysteine c) Glycine d) Alanine

b) Cysteine

What is the major metabolic consequence of decreased NADPH in RBCs? a) Increased ATP b) Decreased reduced glutathione c) Increased ribose production d) Decreased glycolytic intermediates

b) Decreased reduced glutathione

Clinical protection against malaria is observed in the presence of: a) Excess glucose b) G6PD deficiency c) High NADPH d) Ribose-5-P deficiency

b) G6PD deficiency

Biosynthesis of which vitamin requires NADPH as a reductant? a) Vitamin B6 b) Vitamin D c) Vitamin K d) Vitamin B12

b) Vitamin D

Which of the following is a function of NADPH in neurotransmitter synthesis? a) Reducing ribonucleotide to deoxyribonucleotide b) Formation of nitric oxide from arginine c) Inhibiting synaptic vesicle release d) Producing acetylcholine from choline

b) Formation of nitric oxide from arginine

A deficiency in which pathway will impair nucleotide and nucleic acid biosynthesis? a) PPP b) TCA cycle c) Beta-oxidation d) Glycolysis

a) PPP

How does NADPH help prevent methemoglobinemia in RBCs? a) By reducing methemoglobin to hemoglobin via glutathione system b) By synthesizing ATP c) By producing CO2 d) By promoting glycolytic flux

a) By reducing methemoglobin to hemoglobin via glutathione system

Name the rate-limiting enzyme of the oxidative phase in PPP.

Glucose-6-phosphate dehydrogenase

Identify the molecule that acts as the hydrogen acceptor in the PPP oxidative reactions.

NADP+

Name the enzyme that hydrolyzes 6-phosphogluconolactone to 6-phosphogluconate.

Gluconolactonase (Lactonase)

Name the enzyme responsible for converting ribulose-5-phosphate into ribose-5-phosphate.

Ribulose-5-phosphate isomerase

Name the enzyme used to assay thiamine deficiency related to PPP function

Transketolase

Identify the pentose sugar involved in nucleotide synthesis produced by PPP

Ribulose-5-phosphate

Which ion acts as a cofactor for glucose-6-phosphate dehydrogenase

Mg2+ (or Ca2+)

Name the ketopentose formed in the oxidative phase of PPP

Ribulose-5-phosphate

What is the primary substrate for erythrose 4-phosphate and fructose 6-phosphate formation?

Sedoheptulose 7-phosphate

Name the intermediate converted to fructose 6-phosphate and glyceraldehyde 3-phosphate in the non-oxidative phase

Sedoheptulose 7-phosphate

Identify the toxic oxidative molecule converted to water by the glutathione system in RBCs

Hydrogen peroxide (H2O2)

What is the name of the enzyme that converts ribulose-5-phosphate to xylulose-5-phosphate?

Ribulose-5-phosphate 3-epimerase

Which compound inhibits glucose-6-phosphate dehydrogenase by allosteric inhibition?

NADPH

TRUE OR FALSE: NADPH produced in PPP is essential for fatty acid and steroid synthesis.

True

TRUE OR FALSE: Ribose-5-phosphate is directly used for purine and pyrimidine synthesis.

True

TRUE OR FALSE: Glutathione reductase requires NADPH to maintain reduced glutathione.

True

TRUE OR FALSE: Glucose 6-phosphate dehydrogenase deficiency is an autosomal dominant disorder

False

TRUE OR FALSE: High NADPH levels stimulate glucose 6-phosphate dehydrogenase activity

False

TRUE OR FALSE: Transketolase requires FAD as a coenzyme

False

TRUE OR FALSE: Heinz bodies are aggregates of oxidized hemoglobin formed in G6PD deficiency

True

TRUE OR FALSE: The PPP is a metabolic pathway that branches off from glycolysis at fructose 6-phosphate

False

TRUE OR FALSE: NADPH is required for the detoxification of xenobiotics by cytochrome P450 enzymes

True

TRUE OR FALSE: A deficiency in glucose 6-phosphate dehydrogenase decreases NADPH synthesis.

True

TRUE OR FALSE: the PPP is found in actively dividing tissues (e.g. reproductive organ and breast during lactation)

True

TRUE OR FALSE: PPP does not occur in muscles

True

used in reductive reactions A. NAD+ B. NADP+

B. NADP+

used in oxidize substrates A. NAD+ B. NADP+

A. NAD+