Carbohydrate Metabolism

Topics in this chapter

• Glycolysis and Regulation
• Gluconeogenesis and Cori Cycle
• Glycogen Metabolism and Storage Diseases
• Pentose Phosphate Pathway and G6PD
• Galactose Metabolism and Disorders
• TCA Cycle and Metabolic Integration
• Ethanol and Amino Acid Metabolism
• Inborn Errors and Enzyme Deficiencies

Practice questions

1. Question 1Q-A0ADEE

   A 6-month-old infant is brought to the emergency department with recurrent episodes of severe fasting hypoglycemia, hepatomegaly, and doll-like facies. Laboratory investigations reveal marked hyperuricemia, hyperlactatemia, and hyperlipidemia. A liver biopsy shows accumulation of glycogen with normal structure. Which of the following enzyme deficiencies is most likely responsible for this clinical presentation?

   1. A.Glucose-6-phosphatase
   2. B.Alpha-1,4-glucosidase
   3. C.Glycogen phosphorylase
   4. D.Amylo-1,6-glucosidase
   See the answer and solution
2. Question 2Q-F84BB6

   An adult male presents with chronic fatigue and dark pigmentation of the sclera (ochronosis). He also reports that his urine turns dark upon standing and exposure to air. This condition is caused by a metabolic defect in the degradation of which of the following amino acids, which is closely linked to carbohydrate-derived energy pathways?

   1. A.Phenylalanine and Tyrosine
   2. B.Valine and Isoleucine
   3. C.Tryptophan
   4. D.Methionine
   See the answer and solution
3. Question 3Q-0DE2DF

   During high-intensity anaerobic exercise, skeletal muscle generates large amounts of lactate. This lactate is transported via the blood to the liver, where it is converted back into glucose to maintain blood glucose levels. What is the net ATP cost (in equivalents) required by the liver to synthesize one molecule of glucose from two molecules of lactate via this cycle?

   1. A.2 ATP
   2. B.4 ATP
   3. C.6 ATP
   4. D.8 ATP
   See the answer and solution
4. Question 4Q-E14DEC

   A 45-year-old chronic alcoholic is brought to the hospital in an unarousable state following a binge-drinking episode. He has not eaten for the past two days. Laboratory tests reveal profound hypoglycemia with an unexpectedly low level of circulating alanine and lactate, and an elevated NADH/NAD+ ratio in the liver. Which key regulatory enzyme of gluconeogenesis is primarily inhibited under these conditions?

   1. A.Pyruvate carboxylase
   2. B.Phosphoenolpyruvate carboxykinase (PEPCK)
   3. C.Fructose-1,6-bisphosphatase
   4. D.Glucose-6-phosphatase
   See the answer and solution
5. Question 5Q-2DF1D3

   Which of the following regulatory molecules acts as a potent allosteric activator of phosphofructokinase-1 (PFK-1) in the liver, signaling a high energy state and abundance of carbon skeletons for glycolysis?

   1. A.ATP
   2. B.Citrate
   3. C.Fructose-2,6-bisphosphate
   4. D.Glucose-6-phosphate
   See the answer and solution