Which of the following is a pentose sugar found in RNA?
Answer: A
Ribose is a pentose sugar (5-carbon sugar) that is a component of RNA. Deoxyribose is found in DNA, while glucose and fructose are hexose sugars.
Q.2Easy
Glycogen is primarily stored in which of the following tissues in humans?
Answer: B
Glycogen, the storage polysaccharide in animals, is primarily stored in the liver (100-120g) and skeletal muscles (400-500g). The liver glycogen maintains blood glucose, while muscle glycogen is used locally.
Q.3Easy
What is the glycosidic linkage present in maltose?
Answer: A
Maltose consists of two glucose units linked by an α(1→4) glycosidic bond. This is a reducing disaccharide formed during starch digestion.
Q.4Easy
Which enzyme catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate?
Answer: B
Phosphoglucose isomerase (PGI) catalyzes the reversible conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis, step 2.
Q.5Easy
Sucrose is composed of which two monosaccharides?
Answer: B
Sucrose (table sugar) is a disaccharide composed of one glucose and one fructose unit linked by an α(1→2) glycosidic bond. It is a non-reducing sugar.
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Q.6Medium
The Maillard reaction occurs between reducing sugars and amino acids, leading to the formation of:
Answer: B
The Maillard reaction is a non-enzymatic browning reaction between carbonyl groups of reducing sugars and amino groups of proteins/amino acids, producing AGEs. This is significant in glycemic control and diabetes complications.
Q.7Medium
In hyperglycemia, excess glucose undergoes polyol pathway conversion. Which enzyme catalyzes the first step?
Answer: A
Aldose reductase catalyzes the reduction of glucose to sorbitol using NADPH. Sorbitol dehydrogenase catalyzes the oxidation of sorbitol to fructose in the second step of the polyol pathway.
Q.8Medium
Which of the following is a branching enzyme in glycogen synthesis?
Answer: B
Glycogen branching enzyme transfers segments of 6-7 glucose residues from the outer chains to create α(1→6) branch points, increasing solubility and accessibility for glycogen phosphorylase.
Q.9Medium
Cori cycle involves recycling of lactate from muscles to liver. Which enzyme is key in converting lactate back to glucose in the liver?
Answer: B
Pyruvate carboxylase catalyzes the first committed step of gluconeogenesis, converting pyruvate to oxaloacetate. Lactate is converted to pyruvate by LDH, then to glucose via gluconeogenesis.
Q.10Medium
The anomeric carbon in glucose is:
Answer: A
The anomeric carbon (C1 in glucose) is the carbon that becomes chiral when the open-chain form cyclizes to form the hemiacetal. This is the site of α/β isomerism.
Q.11Medium
HbA1c levels are used to monitor long-term glycemic control because glucose binds to hemoglobin through:
Answer: B
HbA1c is formed through non-enzymatic glycation of hemoglobin by glucose, reflecting average blood glucose over 2-3 months (RBC lifespan). Normal HbA1c <5.7%, diagnostic for diabetes ≥6.5%.
Q.12Medium
Cellulose differs from starch in that it contains:
Answer: B
Cellulose contains β(1→4) glycosidic bonds linking glucose units, making it indigestible to humans (no cellulase enzyme). Starch contains α(1→4) bonds, which are digestible.
Q.13Medium
In the pentose phosphate pathway, the oxidative phase primarily generates:
Answer: B
The oxidative phase of PPP generates 2 NADPH per glucose-6-phosphate, essential for fatty acid synthesis, cholesterol synthesis, and antioxidant defense (glutathione reduction). This is particularly important in adipose tissue, liver, and RBCs.
Q.14Hard
A patient with galactosemia has a deficiency in which enzyme?
Answer: B
Classic galactosemia results from deficiency of galactose-1-phosphate uridyltransferase (GALT), preventing conversion of galactose-1-phosphate to UDP-galactose. Leads to accumulation of galactose-1-phosphate and galactitol (in polyol pathway), causing cataracts, intellectual disability, and liver damage.
Q.15Hard
Pasteur effect refers to the inhibition of glycolysis by oxidative phosphorylation. In terms of ATP and citrate, which statement is correct?
Answer: D
PFK is inhibited by high ATP, citrate (signal of sufficient acetyl-CoA), and low pH. In aerobic conditions, efficient oxidative phosphorylation produces sufficient ATP, reducing need for glycolysis (Pasteur effect). Citrate is an allosteric inhibitor of PFK.
Q.16Hard
In glycolysis, which step is irreversible under physiological conditions and requires a different enzyme during gluconeogenesis?
Answer: B
The PFK reaction is highly exergonic (ΔG°' = -14.2 kJ/mol) and is essentially irreversible. During gluconeogenesis, fructose-1,6-bisphosphatase catalyzes the reverse reaction. This is a major control point in carbohydrate metabolism.
Q.17Hard
The Warburg effect describes increased glycolysis in cancer cells even in the presence of oxygen. Which enzyme is typically upregulated in cancer cells to support this?
Answer: C
In the Warburg effect, PFK-2 and PKM2 are upregulated. PFK-2 produces fructose-2,6-bisphosphate (a potent PFK-1 activator), while PKM2 (pyruvate kinase isoform) is upregulated in cancer cells. PKM2 also has non-glycolytic functions in cancer metabolism.
Q.18Easy
Which carbohydrate classification includes both monosaccharides and oligosaccharides?
Answer: B
Simple carbohydrates include monosaccharides (glucose, fructose, galactose) and oligosaccharides (2-10 units like sucrose, maltose, lactose). Complex carbohydrates are polysaccharides with >10 units (starch, glycogen, cellulose).
Q.19Medium
In diabetes mellitus type 2, impaired fasting glucose (100-125 mg/dL) is associated with:
Answer: B
Type 2 diabetes is characterized by insulin resistance (defective glucose uptake and utilization) and progressive β-cell dysfunction. Impaired fasting glucose (100-125 mg/dL) is a prediabetic state. Fasting glucose ≥126 mg/dL on 2 occasions is diagnostic for diabetes.
Q.20Easy
Which enzyme catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis?
Answer: A
Phosphoglucose isomerase catalyzes the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate, the second step of glycolysis.
