30 Questions
Which pathway is often referred to as a Hexose monophosphate shunt?
Pentose Phosphate Pathway
Which of the following is NOT a product of the pentose phosphate pathway?
ATP
Which phase of the pentose phosphate pathway generates NADPH?
Oxidative Phase
What is the main function of NADPH in the pentose phosphate pathway?
To be used in anabolic reactions requiring electrons
Which of the following is a tissue with active pentose phosphate pathway?
Liver
Which glycolytic intermediate does the pentose phosphate pathway begin with?
Glucose 6-P
Which of the following is a product of the pentose phosphate pathway?
Glyceraldehyde 3-P
What is the main function of reduced glutathione synthesized by the pentose phosphate pathway?
To protect cells from oxidative damage
What is the pentose sugar produced by the pentose phosphate pathway?
Ribose
Where does the pentose phosphate pathway take place?
Cytosol
Which enzyme is highly specific for NADP+ and is the first site for NADPH formation in the pentose phosphate pathway?
Glucose-6-P dehydrogenase
Which enzyme is responsible for converting ribulose-5-P into xylulose-5-P in the nonoxidative phase of the pentose phosphate pathway?
Ribulose-5-P-epimerase
Which coenzyme is required by transketolase and pyruvate dehydrogenase in their respective reactions?
Thiamine pyrophosphate (TPP)
Which enzyme in the citric acid cycle also has a requirement for thiamine pyrophosphate?
α-Ketoglutarate oxidoreductase
What is the product of the reaction between sedoheptulose 7-P and glyceraldehyde-3-P in the pentose phosphate pathway?
Fructose-6-P + Erythrose-4-P
Which enzyme is most directly impaired in individuals suffering from G6PD deficiency?
Glutathione peroxidase
Which enzyme is responsible for breaking the bond between C2-C3 of a keto sugar in the pentose phosphate pathway?
Transketolase
A man is given antibiotics to treat a bacterial infection and develops an episode of red blood cell lysis. Which of the following enzymes is most likely defective in this patient?
Glucose-6-phosphate dehydrogenase
Which enzyme is responsible for breaking the bond between C3-C4 of a keto sugar in the pentose phosphate pathway?
Transaldolase
What is the regulatory enzyme in the Pentose Phosphate Pathway?
Glucose 6-phosphate dehydrogenase
Which pathway can account for the complete oxidation of glucose?
Glycolysis
What is the tri-peptide composed of glutamate, cysteine, and glycine?
Glutathione
Which vitamin deficiency can lead to beri-beri, a debilitating disease?
Vitamin B1
What is the function of reduced glutathione (GSH) in red blood cells?
Maintain cysteine residues in hemoglobin
Which brain function is affected by thiamine deficiency?
All of the above
Which condition is often clinically seen as black urine under certain conditions?
G6PD deficiency
Which enzyme converts oxidized glutathione (G-S-S-G) to reduced glutathione (G-SH)?
Glutathione reductase
What is the main role of NADPH in the Pentose Phosphate Pathway?
To regenerate GSH from GSSG
What is the ratio that usually inhibits the Glucose 6-phosphate dehydrogenase enzyme?
NADPH/NADP+
What is the role of glutathione peroxidase in the presence of reduced glutathione (GSH)?
Break down hydrogen peroxide
Study Notes
Pentose Phosphate Pathway
- The pentose phosphate pathway is also referred to as the Hexose monophosphate shunt.
- ATP is NOT a product of the pentose phosphate pathway.
- The oxidative phase of the pentose phosphate pathway generates NADPH.
- The main function of NADPH in the pentose phosphate pathway is to provide reducing power for various biochemical reactions.
Tissues and Function
- Erythrocytes, testes, and lactating mammary glands are tissues with active pentose phosphate pathway.
- The pentose phosphate pathway begins with glucose-6-phosphate, a glycolytic intermediate.
Products and Byproducts
- Ribose-5-phosphate is a product of the pentose phosphate pathway.
- The main function of reduced glutathione synthesized by the pentose phosphate pathway is to protect RBCs against oxidative damage.
Enzymes and Coenzymes
- Glucose-6-phosphate dehydrogenase is the first site for NADPH formation in the pentose phosphate pathway and is highly specific for NADP+.
- Phosphopentomutase is the enzyme responsible for converting ribulose-5-P into xylulose-5-P in the nonoxidative phase of the pentose phosphate pathway.
- Thiamine pyrophosphate is the coenzyme required by transketolase and pyruvate dehydrogenase in their respective reactions.
- α-Ketoglutarate dehydrogenase is the enzyme in the citric acid cycle that also has a requirement for thiamine pyrophosphate.
Pathway Reactions
- The reaction between sedoheptulose 7-P and glyceraldehyde-3-P in the pentose phosphate pathway produces erythrose 4-phosphate and fructose 6-phosphate.
- Aldolase is the enzyme responsible for breaking the bond between C2-C3 of a keto sugar in the pentose phosphate pathway.
- Aldolase is also responsible for breaking the bond between C3-C4 of a keto sugar in the pentose phosphate pathway.
Deficiencies and Diseases
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency can lead to hemolytic anemia, which can cause red blood cell lysis.
- G6PD deficiency is often clinically seen as black urine under certain conditions.
Vitamin Deficiencies
- Thiamine (Vitamin B1) deficiency can lead to beri-beri, a debilitating disease.
- Wernicke-Korsakoff syndrome is a brain disorder caused by thiamine deficiency.
Glutathione
- Glutathione is a tri-peptide composed of glutamate, cysteine, and glycine.
- Reduced glutathione (GSH) protects RBCs against oxidative damage.
- Glutathione reductase is the enzyme that converts oxidized glutathione (G-S-S-G) to reduced glutathione (G-SH).
- Glutathione peroxidase, in the presence of reduced glutathione (GSH), reduces hydrogen peroxide to water.
Regulation and Ratio
- Glucose-6-phosphate dehydrogenase is the regulatory enzyme in the Pentose Phosphate Pathway.
- A high NADPH/NADP+ ratio usually inhibits the Glucose 6-phosphate dehydrogenase enzyme.
Test your knowledge on the Pentose Phosphate Pathway and its connection to glycolysis with this quiz.
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