Which of the following correctly describes the role of carnitine in fatty acid metabolism?

The correct answer is B: It transports long-chain fatty acids across the mitochondrial membrane. Carnitine, via carnitine palmitoyltransferase (CPT), transfers long-chain fatty acyl groups across the inner mitochondrial membrane, enabling their oxidation in the matrix.

A newborn presents with jaundice, hepatomegaly, and infantile cataracts. Laboratory findings show elevated galactose in blood and urine. Which enzyme deficiency is most likely?

The correct answer is C: Galactose-1-phosphate uridylyltransferase deficiency. Classical galactosemia results from galactose-1-phosphate uridylyltransferase (GALT) deficiency, causing accumulation of galactose-1-phosphate which is toxic to liver, brain, and lens. This leads to the classic triad of neonatal jaundice, hepatomegaly, and cataracts. Early dietary restriction of lac

Which of the following amino acids is classified as nonpolar and hydrophobic?

The correct answer is A: Leucine. Leucine is a nonpolar, hydrophobic amino acid with an isobutyl side chain. Serine and threonine are polar uncharged, while aspartate is acidic and polar.

In the Michaelis-Menten equation, what does Km represent when Km >> [S]?

The correct answer is C: The reaction is first-order with respect to substrate concentration. When Km >> [S], the Michaelis-Menten equation simplifies to v = (Vmax/Km)[S], making the reaction essentially first-order. The enzyme has low affinity for substrate under these conditions.

Which enzyme is responsible for the esterification of cholesterol in the bloodstream?

The correct answer is B: Lecithin-cholesterol acyltransferase (LCAT). LCAT esterifies free cholesterol on lipoprotein surfaces, forming cholesterol esters that move to the hydrophobic core. This process is essential for lipoprotein maturation.

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Biochemistry
Carbohydrates

Metabolic pathways, enzymes, proteins

24 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–24 of 24

Topics in Biochemistry

All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78

Q.21 Hard Carbohydrates

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?

A Phosphofructokinase-2 (PFK-2)

B Pyruvate kinase M2 (PKM2)

C Both A and B

D Pyruvate dehydrogenase

Correct Answer: C. Both A and B

EXPLANATION

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.

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Q.22 Hard Carbohydrates

In glycolysis, which step is irreversible under physiological conditions and requires a different enzyme during gluconeogenesis?

A Glucose to Glucose-6-phosphate

B Fructose-6-phosphate to Fructose-1,6-bisphosphate

C Phosphoenolpyruvate to Pyruvate

D Glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate

Correct Answer: B. Fructose-6-phosphate to Fructose-1,6-bisphosphate

EXPLANATION

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.

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Q.23 Hard Carbohydrates

Pasteur effect refers to the inhibition of glycolysis by oxidative phosphorylation. In terms of ATP and citrate, which statement is correct?

A High ATP and acetyl-CoA inhibit phosphofructokinase

B High ATP and citrate inhibit phosphofructokinase

C Low ATP activates phosphofructokinase

D Both B and C are correct

Correct Answer: D. Both B and C are correct

EXPLANATION

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.

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Q.24 Hard Carbohydrates

A patient with galactosemia has a deficiency in which enzyme?

A Galactokinase

B Galactose-1-phosphate uridyltransferase

C UDP-galactose-4-epimerase

D Lactase

Correct Answer: B. Galactose-1-phosphate uridyltransferase

EXPLANATION

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.

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