In the Cori cycle, lactate produced in muscle is converted to glucose in the liver. Which enzyme is crucial for the final step in hepatic gluconeogenesis?
Answer: B
Glucose-6-phosphatase catalyzes the dephosphorylation of glucose-6-phosphate to free glucose, which is the final and rate-limiting step of hepatic gluconeogenesis.
Q.42Hard
Which adaptation occurs in skeletal muscle during prolonged fasting (>48 hours)?
Answer: B
After 24-48 hours of fasting, muscle glycogen is depleted. Muscle shifts to oxidizing amino acids (from proteolysis) and utilizing ketone bodies produced by the liver.
Q.43Hard
A patient with G6PD deficiency may develop hemolytic anemia upon exposure to oxidative stress. This occurs because:
Answer: A
G6PD deficiency reduces NADPH production, decreasing reduced glutathione (GSH) levels. GSH protects RBC membranes from oxidative damage, so its depletion leads to hemolysis.
Q.44Hard
Which of the following correctly describes the allosteric regulation of glycogen phosphorylase in muscle?
Answer: C
In muscle, phosphorylase a (phosphorylated form) is active. It is further activated by AMP, which signals energy depletion during exercise.
Q.45Hard
In maple syrup urine disease (MSUD), accumulation of branched-chain amino acids affects carbohydrate metabolism by:
Answer: C
BCAA metabolism produces acetyl-CoA and increases the acetyl-CoA/CoA ratio, which inhibits pyruvate dehydrogenase, reducing glucose oxidation and affecting carbohydrate metabolism.
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Q.46Hard
Which statement accurately describes the relationship between blood glucose regulation and the Warburg effect in cancer cells?
Answer: D
The Warburg effect describes the metabolic shift in cancer cells toward anaerobic glycolysis, producing lactate even in the presence of oxygen, resulting in high glucose consumption.
Q.47Hard
Which statement best explains the structural basis for the higher energy content of glucose compared to other hexoses?
Answer: C
All hexoses yield approximately the same amount of ATP (~32-38 ATP) through complete oxidation. The ATP yield depends on the metabolic pathways utilized, not intrinsic energy differences.
Q.48Hard
A 6-year-old child presents with muscle pain and myoglobinuria after exercise. Muscle biopsy shows normal glycogen structure but elevated content. This is consistent with:
Answer: B
McArdle disease (GSD Type V) results from muscle phosphorylase deficiency. Glycogen accumulates but is structurally normal. Exercise intolerance and myoglobinuria are characteristic.
Q.49Hard
A diabetic patient shows impaired glucose utilization despite high blood glucose. Which enzyme's activity is most likely reduced?
Answer: A
In diabetes, impaired insulin secretion (due to reduced glucokinase in beta cells) leads to inadequate glucose sensing and utilization by tissues despite hyperglycemia.
Q.50Hard
A patient with aldolase deficiency in fructose-1,6-bisphosphate (Class I aldolase) would show impaired glycolysis primarily because:
Answer: B
Aldolase A catalyzes the cleavage of fructose-1,6-bisphosphate into DHAP and G3P. Its deficiency blocks glycolysis at this critical step.
Q.51Hard
In the non-oxidative phase of the pentose phosphate pathway, ribulose-5-phosphate is converted to ribose-5-phosphate by the enzyme ribulose-5-phosphate isomerase. Which tissue shows MAXIMUM activity of this pathway and why?
Answer: C
Bone marrow shows the highest pentose phosphate pathway activity because rapidly dividing cells require maximum ribose-5-phosphate for nucleotide (DNA/RNA) synthesis during cell division. While adipose tissue needs NADPH for lipogenesis and RBCs need it for antioxidant defense, bone marrow's continuous hematopoiesis demands the most nucleotide precursors. This is clinically relevant in leukemia and chemotherapy patients.
Q.52Hard
A clinical test shows high triglycerides and low HDL cholesterol. What metabolic condition might be indicated?
Answer: B
High triglycerides with low HDL is characteristic of metabolic syndrome, often associated with insulin resistance, obesity, and increased cardiovascular risk.
Q.53Hard
In the mobilization of fatty acids from adipose tissue, which hormone plays the primary regulatory role?
Answer: B
Epinephrine and glucagon activate hormone-sensitive lipase via cAMP signaling in adipose tissue, promoting lipolysis and release of free fatty acids during fasting or stress.
Q.54Hard
Which of the following conditions results from deficiency of lipoprotein lipase?
Answer: A
Lipoprotein lipase deficiency causes Type I hyperlipoproteinemia with severe accumulation of chylomicrons and triglycerides (>1000 mg/dL), risk of acute pancreatitis.
Q.55Hard
What is the net ATP yield from complete oxidation of one molecule of a 16-carbon saturated fatty acid (palmitate)?
Answer: B
Palmitate (C16) undergoes 7 cycles of beta-oxidation producing 8 acetyl-CoA molecules, 7 FADH2, and 7 NADH. Total ATP yield is approximately 129 ATP (accounting for initial activation cost).
Q.56Hard
Apolipoproteins serve multiple functions in lipid transport. Which apolipoprotein is most important for HDL maturation and cholesterol efflux?
Answer: B
ApoA-I is the major apolipoprotein of HDL, essential for LCAT activation and cholesterol esterification, promoting reverse cholesterol transport and HDL maturation.
Q.57Hard
In the synthesis of eicosanoids, what is the first critical step?
Answer: B
Eicosanoid synthesis begins with phospholipase A2-mediated release of arachidonic acid (C20 polyunsaturated fatty acid) from membrane phospholipids, which then serves as substrate for COX and LOX pathways.
Q.58Hard
A 45-year-old patient presents with xanthomas and corneal arcus. Which lipid abnormality is most consistent with these clinical signs?
Answer: B
Xanthomas (lipid deposits in skin and tendons) and corneal arcus (lipid deposition in cornea) are hallmark signs of severe hypercholesterolemia, typically with very high LDL cholesterol levels.
Q.59Hard
Which of the following correctly describes the relationship between LDL particle size and cardiovascular risk?
Answer: A
Small, dense LDL particles (Pattern B) are more atherogenic because they penetrate arterial walls more easily, are more susceptible to oxidation, and have reduced hepatic clearance compared to large, buoyant LDL particles.
Q.60Hard
A patient with Tangier disease shows extremely low HDL levels (<5 mg/dL). This condition results from defective:
Answer: B
Tangier disease results from mutations in ABCA1 gene, which encodes an ATP-binding cassette transporter essential for HDL biogenesis. This leads to severe HDL deficiency and cholesterol accumulation in tissues.
