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.

Which amino acid is essential for the formation of collagen's triple helix structure?

The correct answer is D: All of the above. Glycine (every third residue) provides flexibility, proline stabilizes the polyproline II helix conformation, and hydroxyproline (formed by post-translational modification) stabilizes the triple helix through additional hydrogen bonding.

Which statement about peptide bonds is correct?

The correct answer is A: They are formed between the carboxyl group of one amino acid and the amino group of another with release of water. Peptide bonds form through a condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another, releasing H2O. They are covalent and stable.

A protein exhibits a β-sheet structure rich in proline residues. Why is this structurally problematic?

The correct answer is A: Proline lacks a free NH group to form backbone hydrogen bonds in β-sheets. Proline is an imino acid with its side chain bonded to the backbone nitrogen, eliminating the NH group needed for β-sheet hydrogen bonding between strands. High proline content disrupts β-sheet formation, commonly found in turns and loops instead.

In glycogen synthesis, which enzyme transfers glucose from UDP-glucose to the growing glycogen chain?

The correct answer is B: Glycogen synthase. Glycogen synthase catalyzes the transfer of glucose from UDP-glucose to the C4-OH group of the terminal glucose in glycogen, forming α-1,4-glycosidic bonds.

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Biochemistry
Lipids

Metabolic pathways, enzymes, proteins

36 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–36 of 36

Topics in Biochemistry

All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78

Q.31 Medium Lipids

A person consumes excessive saturated fats. Which lipoprotein level is most likely to increase?

A HDL (High-Density Lipoprotein)

B VLDL (Very Low-Density Lipoprotein)

C LDL derived from VLDL remains unchanged

D Chylomicrons remain stable

Correct Answer: B. VLDL (Very Low-Density Lipoprotein)

EXPLANATION

Excessive dietary saturated fat increases liver production of VLDL, which carries triglycerides and cholesterol. VLDL is converted to LDL in circulation, raising LDL levels.

Test

Q.32 Medium Lipids

Phospholipids differ from triglycerides in that they contain:

A Four fatty acid chains instead of three

B A phosphate group and typically only two fatty acids

C No glycerol backbone

D Cholesterol instead of glycerol

Correct Answer: B. A phosphate group and typically only two fatty acids

EXPLANATION

Phospholipids have a glycerol backbone with two fatty acids and a phosphate group, making them amphipathic. This structure is crucial for membrane formation.

Test

Q.33 Medium Lipids

Which enzyme catalyzes the rate-limiting step of cholesterol synthesis?

A Acetyl-CoA carboxylase

B HMG-CoA reductase

C Fatty acid synthase

D Lipoprotein lipase

Correct Answer: B. HMG-CoA reductase

EXPLANATION

HMG-CoA reductase catalyzes the conversion of HMG-CoA to mevalonate, the rate-limiting and key regulatory step in cholesterol biosynthesis. It is targeted by statin drugs.

Test

Q.34 Medium Lipids

A patient with familial hypercholesterolemia shows extremely high cholesterol levels. What is the most likely defect?

A Deficiency in HMG-CoA reductase

B Absence or malfunction of LDL receptors

C Excessive HDL production

D Decreased acetyl-CoA levels

Correct Answer: B. Absence or malfunction of LDL receptors

EXPLANATION

Familial hypercholesterolemia is caused by mutations in the LDL receptor gene, preventing cells from taking up LDL particles, resulting in elevated blood cholesterol levels.

Test

Q.35 Medium Lipids

Which of the following is a consequence of excessive cholesterol accumulation in arteries?

A Increased blood viscosity leading to faster flow

B Formation of atherosclerotic plaques causing narrowing of arteries

C Enhanced oxygen delivery to tissues

D Improved arterial elasticity

Correct Answer: B. Formation of atherosclerotic plaques causing narrowing of arteries

EXPLANATION

High cholesterol, particularly LDL cholesterol, can accumulate in artery walls forming atherosclerotic plaques, leading to arterial narrowing (atherosclerosis) and increased risk of heart disease.

Test

Q.36 Medium Lipids

In the context of lipid metabolism, what does beta-oxidation primarily accomplish?

A Synthesis of new fatty acids

B Breaking down fatty acids into acetyl-CoA for energy production

C Formation of cholesterol from acetyl-CoA

D Conversion of glucose into triglycerides

Correct Answer: B. Breaking down fatty acids into acetyl-CoA for energy production

EXPLANATION

Beta-oxidation is the catabolic pathway that breaks down fatty acids in the mitochondria, producing acetyl-CoA which enters the Krebs cycle for ATP production.

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