HMP shunt (AKA pentose phosphate pathway) Flashcards
(20 cards)
A 24-year-old male presents with fatigue and jaundice after eating fava beans. Blood smear shows Heinz bodies. Which enzyme deficiency is most likely responsible for his symptoms?
A) Pyruvate kinase
B) Glucose-6-phosphatase
C) Glucose-6-phosphate dehydrogenase
D) Transaldolase
E) Fructokinase
Answer: C Glucose-6-phosphate
Why: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common cause of oxidative damage in RBCs, leading to hemolysis and Heinz bodies after exposure to oxidative stress like fava beans.
A 60-year-old alcoholic man shows signs of Wernicke’s encephalopathy. Which cofactor deficiency in the HMP shunt contributes to his condition?
A) FAD
B) NAD+
C) Thiamine (B1)
D) Biotin
E) Pyridoxine (B6)
Answer: C
Why: Thiamine is a required cofactor for transketolase in the HMP shunt. Its deficiency leads to impaired glucose metabolism, especially in the brain.
Which of the following is a major function of the HMP shunt?
A) Produce ATP from glucose
B) Generate NADH for oxidative phosphorylation
C) Synthesize glucose from non-carbohydrates
D) Generate NADPH and ribose-5-phosphate
E) Store glucose as glycogen
Answer: D
Why: The HMP shunt produces NADPH (for reductive biosynthesis and protection against oxidative stress) and ribose-5-phosphate (for nucleotide synthesis).
A newborn is diagnosed with a deficiency in glucose-6-phosphate dehydrogenase. Which of the following pathways will be impaired?
A) Glycogenolysis
B) Glycolysis
C) Pentose phosphate pathway
D) Beta-oxidation
E) TCA cycle
Answer: C
Why: G6PD is the rate-limiting enzyme of the HMP shunt (pentose phosphate pathway). Its deficiency impairs NADPH production.
Which of the following best describes the role of NADPH generated in the HMP shunt in red blood cells?
A) ATP generation
B) Protein phosphorylation
C) Oxidative phosphorylation
D) Reduction of glutathione
E) Glycogen synthesis
Answer: D
Why: NADPH maintains reduced glutathione, which detoxifies ROS in RBCs.
What is the rate-limiting enzyme of the HMP shunt?
A) Transaldolase
B) Glucose-6-phosphate dehydrogenase
C) Phosphofructokinase
D) Lactate dehydrogenase
E) Hexokinase
Answer: B
Why: G6PD is the first and rate-limiting enzyme in the oxidative phase of the HMP shunt.
A cell needs to make nucleotides but does not require NADPH. Which phase of the HMP shunt will be primarily active?
A) Oxidative
B) Non-oxidative
C) Gluconeogenic
D) Glycolytic
E) Mitochondrial
Answer: B
Why: The non-oxidative phase produces ribose-5-phosphate for nucleotide synthesis without generating NADPH.
Which of the following best explains why glucose-6-phosphate dehydrogenase deficiency causes hemolytic anemia?
A) Lack of ribose-5-phosphate synthesis
B) Decreased ATP synthesis
C) Accumulation of pyruvate
D) Inability to detoxify reactive oxygen species
E) Overproduction of ketone bodies
Answer: D
Why: G6PD deficiency results in low NADPH, which impairs glutathione regeneration and leads to oxidative damage in RBCs.
Which of the following vitamins is needed by transketolase in the HMP shunt?
A) Vitamin C
B) Vitamin B6
C) Vitamin B1
D) Vitamin B3
E) Vitamin B12
Answer: C
Why: Thiamine (B1) is a required cofactor for transketolase, a key enzyme in the non-oxidative phase.
A patient with G6PD deficiency receives trimethoprim-sulfamethoxazole and develops dark urine and fatigue. What is the most likely cause?
A) Hepatic failure
B) Hemolysis due to oxidative stress
C) Acute renal failure
D) Respiratory acidosis
E) Autoimmune anemia
Answer: B
Why: Sulfa drugs trigger oxidative stress, and G6PD deficiency prevents detoxification, leading to hemolysis.
Which metabolic product of the HMP shunt is essential for fatty acid and cholesterol synthesis?
A) ATP
B) NADH
C) NADPH
D) Acetyl-CoA
E) Ribose
Answer: C
Why: NADPH is required for reductive biosynthesis like fatty acid and cholesterol synthesis.
In G6PD deficiency, what compensatory change occurs in RBCs under oxidative stress?
A) Increased glycolysis
B) Formation of Howell-Jolly bodies
C) Increased hemoglobin synthesis
D) Splenic removal of Heinz bodies
E) Increased oxygen affinity of hemoglobin
Answer: D
Why: Damaged RBCs form Heinz bodies, which are removed by the spleen, causing “bite cells.”
Which of the following cells relies heavily on NADPH for the respiratory burst?
A) Hepatocytes
B) Red blood cells
C) Neurons
D) Neutrophils
E) Enterocytes
Answer: D
Why: Neutrophils require NADPH to generate superoxide for microbial killing.
Which of the following best explains why NADPH is important in detoxification reactions?
A) NADPH oxidizes toxins directly
B) NADPH regenerates NAD+
C) NADPH is used by cytochrome P450 enzymes
D) NADPH synthesizes hemoglobin
E) NADPH catalyzes fatty acid oxidation
Answer: C
Why: NADPH donates electrons to cytochrome P450 enzymes, which are crucial in detox reactions.
A patient with G6PD deficiency is exposed to an oxidant. Which of the following lab findings would you most expect?
A) Hyperkalemia
B) Hemoglobinuria
C) Increased serum AST
D) Elevated urea
E) Hypocalcemia
Answer: B
Why: Hemolysis releases hemoglobin into the urine, resulting in hemoglobinuria.
A cell has high levels of NADPH. What effect will this have on glucose-6-phosphate dehydrogenase activity?
A) Increase it
B) Inhibit it
C) No effect
D) Activate transketolase
E) Increase glycolysis
Answer: B
Why: NADPH is a feedback inhibitor of G6PD, the rate-limiting enzyme.
Which metabolic pathway shares glucose-6-phosphate as a starting substrate with the HMP shunt?
A) Glycolysis
B) TCA cycle
C) Urea cycle
D) Beta-oxidation
E) Ketogenesis
Answer: A
Why: Both glycolysis and the HMP shunt begin with glucose-6-phosphate.
A 35-year-old man with no history of anemia begins taking dapsone. He becomes jaundiced and pale. What is the first test you should order?
A) Hemoglobin electrophoresis
B) Serum ferritin
C) Reticulocyte count
D) G6PD assay
E) Bone marrow biopsy
Answer: D
Why: Dapsone is an oxidant drug. G6PD testing is indicated to confirm hemolysis due to enzyme deficiency.
Which of the following is a product of the non-oxidative phase of the HMP shunt?
A) NADH
B) Glyceraldehyde-3-phosphate
C) Glucose
D) Pyruvate
E) Lactate
Answer: B
Why: The non-oxidative phase interconverts sugars, including glyceraldehyde-3-phosphate.
