T2. PENTOSE PHOSPHATE PATHWAY Flashcards
(30 cards)
What are the primary functions of the Pentose Phosphate Pathway (PPP)?
Generates NADPH for anabolic reactions and ribose-5-phosphate for nucleotide synthesis.
Where in the cell does the PPP occur?
In the cytosol of cells.
Which tissues have high PPP activity?
Tissues involved in biosynthesis and detoxification, such as liver, adipose tissue, adrenal glands, and erythrocytes.
What are the two phases of the PPP?
Oxidative (irreversible) and non-oxidative (reversible) phases.
What occurs during the oxidative phase of the PPP?
Oxidation of glucose-6-phosphate to ribulose-5-phosphate, producing NADPH.
Which enzyme catalyzes the first step of the oxidative phase?
Glucose-6-phosphate dehydrogenase (G6PD).
What is the role of NADPH produced in the PPP?
Provides reducing power for biosynthetic reactions and antioxidant defense.
What occurs during the non-oxidative phase of the PPP?
Reversible interconversion of sugars to produce ribose-5-phosphate and glycolytic intermediates.
Which enzymes are involved in the non-oxidative phase?
Transketolase and transaldolase.
: What cofactor is required by transketolase?
Thiamine pyrophosphate (TPP).
How is the PPP regulated in the short term?
By the NADP+/NADPH ratio; high NADP+ activates G6PD, while high NADPH inhibits it.
How is the PPP regulated in the long term?
Insulin induces the expression of G6PD, increasing PPP activity.
What is Mode 1 of PPP operation?
Cells need more ribose-5-phosphate than NADPH; non-oxidative phase runs in reverse to generate ribose-5-phosphate from glycolytic intermediates.
What is Mode 2 of PPP operation?
Balanced need for NADPH and ribose-5-phosphate; only the oxidative phase operates.
What is Mode 3 of PPP operation?
Cells need more NADPH than ribose-5-phosphate; both phases operate, and glycolytic intermediates are recycled back to glucose-6-phosphate.
What is Mode 4 of PPP operation?
Cells need NADPH and ATP; glycolytic intermediates from the PPP enter glycolysis for ATP production.
How does the PPP protect against reactive oxygen species (ROS)?
NADPH from the PPP reduces glutathione, which detoxifies ROS.
What is the role of glutathione in cells?
Acts as an antioxidant by neutralizing ROS.
What happens in G6PD deficiency?
Reduced NADPH production leads to decreased glutathione regeneration, making red blood cells susceptible to oxidative damage and hemolysis.
What triggers hemolytic anemia in G6PD deficiency?
Oxidative stress from infections, certain drugs, or foods like fava beans.
What are symptoms of hemolytic anemia due to G6PD deficiency?
Fatigue, jaundice, dark urine, and shortness of breath.
How is thiamine deficiency related to the PPP?
Thiamine is a cofactor for transketolase; its deficiency impairs the non-oxidative phase of the PPP.
What are symptoms of thiamine deficiency?
Memory loss, confusion, and neurological issues.
What is Wernicke-Korsakoff syndrome?
A neurological disorder caused by severe thiamine deficiency, leading to memory problems and confusion.
