In protein synthesis, which aminoacyl-tRNA synthetase error rate is approximately 1 in 10,000, ensuring high fidelity?

The correct answer is B: Through a proofreading mechanism that hydrolyzes incorrectly charged tRNA. Aminoacyl-tRNA synthetases achieve high fidelity through a two-step selection process: initial selection during aminoacylation and a second proofreading step (editing) that hydrolyzes incorrectly charged tRNA-amino acid complexes before they leave the enzyme.

A patient with Tangier disease shows extremely low HDL levels (

The correct answer is B: ABCA1 transporter. Tangier disease results from mutations in ABCA1 gene, which encodes an ATP-binding cassette transporter essential for HDL biogenesis. This leads to severe HDL deficiency and cholesterol accumulation in tissues.

What is the structural role of zinc in alcohol dehydrogenase?

The correct answer is B: Zinc coordinates the substrate and facilitates hydride transfer. Alcohol dehydrogenase contains catalytic zinc that coordinates the hydroxyl group of ethanol/aldehyde substrate, activating it for hydride transfer to NAD+, and structural zinc that maintains protein stability.

Which of the following lipids is NOT a structural component of cell membranes?

The correct answer is D: Triacylglycerol. Triacylglycerols are storage lipids found primarily in adipose tissue. Phosphatidylcholine, cholesterol, and sphingomyelin are major components of cell membranes.

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?

The correct answer is C: Both A and B. 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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Biochemistry

Metabolic pathways, enzymes, proteins

72 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 71–72 of 72

Topics in Biochemistry

All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78

Q.71 Easy Proteins & Enzymes

The primary structure of a protein is stabilized by which type of bond?

A Hydrogen bonds

B Peptide bonds

C Ionic bonds

D Disulfide bridges

Correct Answer: B. Peptide bonds

EXPLANATION

Peptide bonds between the carboxyl group of one amino acid and the amino group of the next maintain the primary structure.

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Q.72 Easy Proteins & Enzymes

Which of the following amino acids is NOT classified as a standard protein amino acid?

A Selenocysteine

B Alanine

C Glycine

D Valine

Correct Answer: A. Selenocysteine

EXPLANATION

Selenocysteine is the 21st amino acid and is not among the standard 20 protein amino acids. It contains selenium instead of sulfur.

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