2025 PR221 Carbohydrate Metabolism

A 24-year-old man collapses during a marathon. Labs show hypoglycemia and low lactate.

Muscle biopsy reveals decreased phosphofructokinase-1 (PFK-1) activity.

Which of the following pathways is directly impaired, contributing to his symptoms?

• Glycogenolysis

• Glycogenesis

• Gluconeogenesis

• Glycolysis

Labs reveal elevated pyruvate and α-ketoglutarate.

Which of the following pathways is most directly impaired?

• Glycogenesis

• Hexose Monophosphate Shunt

• TCA Cycle

• Cori Cycle

A man develops acute hemolytic anemia after eating fava beans. Smear shows Heinz bodies.

What is the primary biochemical defect?

• Impaired NADPH production 

• Impaired NADH generation

• Increased GSH

• Decreased GSSG

A 5-month-old has isolated cataracts. Galactokinase-1 deficiency is confirmed.

Which toxic metabolite is most responsible for symptoms?

• Glucose-1-phosphate

• Galactose-1-phosphate

• Galactitol

• UDP-galactose

A 5-year-old has hepatomegaly, severe fasting hypoglycemia, lactic acidosis, and hyperlipidemia.

Which enzyme is deficient?

• Glucose-6-phosphatase

• Fructose-1,6-bisphosphatase

• Liver glycogen phosphorylase

• Glycogen synthase

Which of the following metabolic pathways involves substrate-level phosphorylation that occurs in both aerobic and anaerobic conditions?

• Citric Acid Cycle

• Respiratory Chain

• Pyruvate Oxidation

• Embden-Meyerhof Pathway

Which of the following enzymes catalyzes the conversion of a 3-carbon organic molecule into acetyl-CoA?

• Pyruvate Kinase

• Pyruvate Decarboxylase

• Pyruvate Dehydrogenase

• Phosphoenolpyruvate Carboxylase

How many molecules of FADH₂ and ATP (from substrate-level phosphorylation) are generated during one turn of the TCA cycle per one molecule of acetyl-CoA?

• 0.5 FADH₂ and 0.5 ATP

• 1 FADH₂ and 1 ATP

• 1 FADH₂ and 2 ATP

• 2 FADH₂ and 2 ATP

All of the following enzymes are involved in gluconeogenesis EXCEPT:

• Pyruvate Kinase

• Glucose-6-phosphatase

• Fructose-1,6-bisphosphatase

• Phosphoenolpyruvate Carboxykinase

In glycolysis, inhibition of which of the following enzymes would most significantly reduce the overall rate of the pathway?

• Hexokinase

• Phosphofructokinase

• Aldolase

• Pyruvate kinase