Which enzyme catalyzes the reversible conversion of glucose-6-phosphate to fructose-6-phosphate?
Answer: B
Phosphoglucose isomerase catalyzes the interconversion of glucose-6-phosphate and fructose-6-phosphate in glycolysis.
Q.82Medium
A patient presents with inability to metabolize galactose. Which enzyme deficiency is most likely responsible for classical galactosemia?
Answer: B
Classical galactosemia results from galactose-1-phosphate uridyltransferase (GALT) deficiency, causing accumulation of galactose-1-phosphate and galactosylated proteins.
Q.83Medium
The branching enzyme in glycogen synthesis catalyzes which type of reaction?
Answer: B
Branching enzyme (amylo-1,6-transglucosidase) transfers segments of α-1,4-linked glucose chains to create α-1,6 branch points in glycogen.
Q.84Medium
During high-intensity exercise, which carbohydrate provides immediate energy despite low concentration in blood?
Answer: B
Muscle glycogen is the primary energy source during high-intensity exercise because muscle lacks glucose-6-phosphatase and retains glucose-6-phosphate for glycolysis.
Q.85Medium
Which of the following is NOT a function of glycogen in liver?
Answer: D
Liver glycogen maintains blood glucose but cannot directly supply glucose-6-phosphate to other tissues as glucose-6-phosphate cannot cross cell membranes.
Advertisement
Q.86Medium
A newborn presents with hepatomegaly, lactic acidosis, and hypoglycemia. Enzyme analysis shows deficiency of glucose-6-phosphatase. Which disease is this?
Answer: C
Von Gierke disease (GSD Type I) results from glucose-6-phosphatase deficiency, preventing final step of both gluconeogenesis and glycogenolysis, causing severe hypoglycemia.
Q.87Medium
In hereditary fructose intolerance (HFI), which enzyme deficiency causes accumulation of fructose-1-phosphate?
Answer: B
HFI results from aldolase B deficiency, preventing cleavage of fructose-1-phosphate into DHAP and glyceraldehyde, leading to accumulation and hepatotoxicity.
Q.88Easy
The optical rotation of freshly prepared glucose solution gradually decreases and reaches equilibrium. This phenomenon is called:
Answer: A
Mutarotation is the spontaneous interconversion between α and β anomers of glucose at the anomeric carbon until equilibrium is reached.
Q.89Hard
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.90Hard
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.91Medium
In the pentose phosphate pathway, the oxidative phase generates NADPH. Which metabolic process primarily utilizes this NADPH in fed state?
Answer: C
NADPH from the oxidative pentose phosphate pathway is essential for reductive biosynthesis of fatty acids and cholesterol, which occur predominantly in the fed state.
Q.92Easy
Which of the following carbohydrates does NOT undergo glycolysis?
Answer: C
Cellulose is a β-1,4-linked glucose polymer that humans cannot digest due to lack of cellulase enzyme. It cannot enter glycolysis.
Q.93Hard
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.94Medium
The Haworth projection of glucose differs from its Fischer projection. Which structural feature is best represented in Haworth projection?
Answer: B
Haworth projection depicts the cyclic hemiacetal structure of glucose in its pyranose form, clearly showing the anomeric carbon and ring geometry.
Q.95Medium
During fasting, which hormonal change directly increases hepatic glycogenolysis?
Answer: B
Glucagon and epinephrine activate phosphorylation cascades that activate glycogen phosphorylase and inactivate glycogen synthase, promoting glycogenolysis.
Q.96Medium
Which adaptation occurs in liver during prolonged fasting to maintain blood glucose?
Answer: B
After 8-12 hours of fasting, hepatic glycogen depletes. The liver then relies on gluconeogenesis from Cori cycle lactate and amino acids to maintain blood glucose.
Q.97Hard
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.98Medium
A 45-year-old patient with Type 2 diabetes mellitus shows elevated fasting blood glucose (180 mg/dL) but normal HbA1c levels initially. Which carbohydrate metabolism pathway is primarily impaired in this patient's liver?
Answer: A
Type 2 diabetes shows hepatic insulin resistance leading to impaired glycogenesis (reduced glycogen synthesis) and uncontrolled gluconeogenesis (excessive glucose production). This causes elevated fasting glucose despite normal HbA1c if glycemic control improves later. The liver fails to suppress glucose production in response to insulin.
Q.99Hard
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.
