Which enzyme is the rate-limiting step of glycolysis and is inhibited by ATP and citrate?
Answer: B
Phosphofructokinase-1 (PFK-1) catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate and is subject to allosteric inhibition by ATP and citrate.
Q.162Easy
What is the net yield of ATP from the anaerobic metabolism of one molecule of glucose?
Answer: A
Anaerobic glycolysis produces 4 ATP molecules but consumes 2 ATP, resulting in a net gain of 2 ATP per glucose molecule.
Q.163Easy
Which of the following is a reducing sugar?
Answer: C
Maltose is a reducing sugar because it has a free anomeric carbon. Sucrose and trehalose are non-reducing sugars as both anomeric carbons are involved in glycosidic bonds.
Q.164Medium
In the citric acid cycle, which carbohydrate-derived molecule enters directly after acetyl-CoA formation?
Answer: D
Acetyl-CoA condenses with oxaloacetate to form citrate, which enters the citric acid cycle. Citrate synthase catalyzes this reaction.
Q.165Medium
Which of the following conditions causes increased glycogenolysis in muscle tissue during exercise?
Answer: B
During exercise, epinephrine increases and ATP/AMP ratio decreases, both of which activate phosphorylase kinase and promote glycogenolysis.
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Q.166Medium
What is the primary fate of pyruvate under anaerobic conditions in muscle during intense exercise?
Answer: C
Under anaerobic conditions, pyruvate is reduced to lactate by lactate dehydrogenase (LDH) to regenerate NAD+ for continued glycolysis.
Q.167Medium
Which enzyme deficiency causes Pompe disease (GSD Type II)?
Answer: B
Pompe disease results from deficiency of acid α-glucosidase (lysosomal α-1,4-glucosidase), leading to accumulation of glycogen in lysosomes, especially in muscles and heart.
Q.168Medium
During the pentose phosphate pathway, which coenzyme is reduced to generate NADPH?
Answer: C
NADP+ is reduced to NADPH in the oxidative phase of the pentose phosphate pathway, primarily in the G6PD and 6-PGD reactions.
Q.169Medium
Which of the following best explains why glycogen is more soluble than starch despite similar glycosidic linkages?
Answer: A
Glycogen has more frequent α-1,6 branch points (approximately every 8-12 glucose units) compared to starch, increasing its solubility and accessibility for enzyme action.
Q.170Medium
In a patient with von Gierke disease, excessive hepatic glucose production is primarily due to:
Answer: C
Von Gierke disease (GSD Type I) involves glucose-6-phosphatase deficiency, leading to impaired glucose release. However, alternative glucose production through gluconeogenesis and pentose phosphate pathway increases.
Q.171Medium
Which of the following substrates can be directly utilized for glycogen synthesis in the liver?
Answer: B
Glucose-1-phosphate is converted to UDP-glucose by UDP-glucose pyrophosphorylase, which is the activated form used by glycogen synthase for glycogen synthesis.
Q.172Hard
A 45-year-old male presents with chronic hyperuricemia and gout. Testing reveals elevated lactic acid and hepatomegaly. Which GSD is most likely?
Answer: B
Von Gierke disease causes hepatomegaly, lactic acidosis, and hyperuricemia due to glucose-6-phosphatase deficiency, leading to increased glycolysis and purine metabolism.
Q.173Hard
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.174Hard
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.175Hard
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.176Hard
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.177Hard
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.
Q.178Hard
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.179Easy
Which of the following carbohydrates is a ketohexose?
Answer: A
Fructose is a ketohexose (6-carbon ketone sugar), while glucose, galactose are aldohexoses, and ribose is a pentose.
Q.180Easy
The disaccharide formed by α-glucose and β-fructose joined by α-1,2-glycosidic bond is:
Answer: C
Sucrose is composed of glucose and fructose linked by α-1,2-glycosidic bond. Maltose has α-1,4 bond between two glucose molecules.
