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Biochemistry

Metabolic pathways, enzymes, proteins

278 Q 3 Topics Take Test
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Difficulty: All Easy Medium Hard 81–90 of 278
Topics in Biochemistry
All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78
Q.81 Hard Carbohydrates
A patient with aldolase deficiency in fructose-1,6-bisphosphate (Class I aldolase) would show impaired glycolysis primarily because:
A Glucose-6-phosphate cannot be converted to fructose-6-phosphate
B Fructose-1,6-bisphosphate cannot be cleaved into triose phosphates
C Pyruvate cannot be formed from glyceraldehyde-3-phosphate
D Lactate cannot be converted to glucose
Correct Answer:  B. Fructose-1,6-bisphosphate cannot be cleaved into triose phosphates
EXPLANATION

Aldolase A catalyzes the cleavage of fructose-1,6-bisphosphate into DHAP and G3P. Its deficiency blocks glycolysis at this critical step.

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Q.82 Medium Carbohydrates
Which adaptation occurs in liver during prolonged fasting to maintain blood glucose?
A Increased glycogenolysis only
B Increased gluconeogenesis from lactate and amino acids
C Increased lipogenesis
D Increased glycogen synthesis
Correct Answer:  B. Increased gluconeogenesis from lactate and amino acids
EXPLANATION

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.

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Q.83 Medium Carbohydrates
During fasting, which hormonal change directly increases hepatic glycogenolysis?
A Increased insulin and decreased glucagon
B Increased glucagon and epinephrine
C Increased cortisol and growth hormone only
D Increased somatostatin levels
Correct Answer:  B. Increased glucagon and epinephrine
EXPLANATION

Glucagon and epinephrine activate phosphorylation cascades that activate glycogen phosphorylase and inactivate glycogen synthase, promoting glycogenolysis.

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Q.84 Medium Carbohydrates
The Haworth projection of glucose differs from its Fischer projection. Which structural feature is best represented in Haworth projection?
A Linear conformation of glucose
B Cyclic hemiacetal structure with anomeric carbon
C Three-dimensional configuration of all carbons
D Stereoisomeric relationships between sugars
Correct Answer:  B. Cyclic hemiacetal structure with anomeric carbon
EXPLANATION

Haworth projection depicts the cyclic hemiacetal structure of glucose in its pyranose form, clearly showing the anomeric carbon and ring geometry.

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Q.85 Hard Carbohydrates
A diabetic patient shows impaired glucose utilization despite high blood glucose. Which enzyme's activity is most likely reduced?
A Glucokinase in beta cells
B Phosphofructokinase in muscle
C Glycogen phosphorylase in liver
D Hexokinase in tissues
Correct Answer:  A. Glucokinase in beta cells
EXPLANATION

In diabetes, impaired insulin secretion (due to reduced glucokinase in beta cells) leads to inadequate glucose sensing and utilization by tissues despite hyperglycemia.

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Q.86 Easy Carbohydrates
Which of the following carbohydrates does NOT undergo glycolysis?
A Glucose
B Mannose
C Cellulose
D Galactose
Correct Answer:  C. Cellulose
EXPLANATION

Cellulose is a β-1,4-linked glucose polymer that humans cannot digest due to lack of cellulase enzyme. It cannot enter glycolysis.

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Q.87 Medium Carbohydrates
In the pentose phosphate pathway, the oxidative phase generates NADPH. Which metabolic process primarily utilizes this NADPH in fed state?
A Glycolysis
B Ketone body synthesis
C Fatty acid and cholesterol synthesis
D Oxidative phosphorylation
Correct Answer:  C. Fatty acid and cholesterol synthesis
EXPLANATION

NADPH from the oxidative pentose phosphate pathway is essential for reductive biosynthesis of fatty acids and cholesterol, which occur predominantly in the fed state.

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Q.88 Hard Carbohydrates
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:
A Branching enzyme deficiency
B Muscle phosphorylase deficiency
C Lysosomal acid maltase deficiency
D Liver phosphorylase deficiency
Correct Answer:  B. Muscle phosphorylase deficiency
EXPLANATION

McArdle disease (GSD Type V) results from muscle phosphorylase deficiency. Glycogen accumulates but is structurally normal. Exercise intolerance and myoglobinuria are characteristic.

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Q.89 Hard Carbohydrates
Which statement best explains the structural basis for the higher energy content of glucose compared to other hexoses?
A Glucose has more hydroxyl groups
B Glucose is more stable and requires less energy for phosphorylation
C All hexoses have identical energy content; ATP yield depends on metabolic pathway efficiency
D Glucose has a unique aldehyde group arrangement
Correct Answer:  C. All hexoses have identical energy content; ATP yield depends on metabolic pathway efficiency
EXPLANATION

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.

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Q.90 Easy Carbohydrates
The optical rotation of freshly prepared glucose solution gradually decreases and reaches equilibrium. This phenomenon is called:
A Mutarotation
B Epimerization
C Isomerization
D Racemization
Correct Answer:  A. Mutarotation
EXPLANATION

Mutarotation is the spontaneous interconversion between α and β anomers of glucose at the anomeric carbon until equilibrium is reached.

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