What is the primary function of chaperone proteins in the endoplasmic reticulum?

The correct answer is A: Facilitating protein folding and preventing aggregation. ER chaperones like BiP (heat shock protein 70) assist in protein folding, prevent aggregation, and aid in proper disulfide bond formation during synthesis.

Which statement best explains the structural basis for the higher energy content of glucose compared to other hexoses?

The correct answer is C: All hexoses have identical energy content; ATP yield depends on metabolic pathway efficiency. 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.

The branching enzyme in glycogen synthesis catalyzes which type of reaction?

The correct answer is B: Transfer of α-1,4-glucose chain segment to α-1,6 position. Branching enzyme (amylo-1,6-transglucosidase) transfers segments of α-1,4-linked glucose chains to create α-1,6 branch points in glycogen.

Which of the following carbohydrates is a heptose?

The correct answer is B: Sedoheptulose. Sedoheptulose is a seven-carbon ketose (heptose) that participates in the non-oxidative phase of the pentose phosphate pathway.

Which enzyme catalyzes the hydrolysis of proteins into smaller polypeptides and amino acids?

The correct answer is B: Protease. Proteases are endopeptidases and exopeptidases that hydrolyze peptide bonds in proteins. Amylase acts on carbohydrates, lipase on fats, and nuclease on nucleic acids.

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Biochemistry
Proteins & Enzymes

Metabolic pathways, enzymes, proteins

27 Q 3 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–27 of 27

Topics in Biochemistry

All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78

Q.21 Hard Proteins & Enzymes

In non-competitive inhibition, what is the graphical representation on a Lineweaver-Burk plot?

A Lines intersect on the y-axis

B Lines intersect on the x-axis

C Lines intersect to the left of the y-axis

D Parallel lines

Correct Answer: A. Lines intersect on the y-axis

EXPLANATION

In non-competitive inhibition, both Km and Vmax are affected proportionally. On a Lineweaver-Burk plot (1/v vs 1/[S]), this results in lines with different slopes that intersect on the y-axis.

Test

Q.22 Hard Proteins & Enzymes

A protease enzyme shows reduced activity when Ca²⁺ is removed from the reaction mixture. This indicates that Ca²⁺ acts as a:

A Substrate

B Allosteric regulator

C Cofactor

D Competitive inhibitor

Correct Answer: C. Cofactor

EXPLANATION

Ca²⁺ is required for enzymatic activity and is not consumed in the reaction, making it a cofactor. Many proteases require metal ions as structural or catalytic cofactors.

Test

Q.23 Hard Proteins & Enzymes

Which statement about the relationship between protein structure and function is INCORRECT?

A Primary structure determines all higher-order structures

B Tertiary structure can exist without secondary structure

C Quaternary structure requires multiple polypeptide chains

D Disulfide bonds stabilize tertiary structure in extracellular proteins

Correct Answer: B. Tertiary structure can exist without secondary structure

EXPLANATION

Tertiary structure requires secondary structure elements. Secondary structures (α-helix, β-sheet) fold into tertiary structure; one cannot exist without the other.

Test

Q.24 Hard Proteins & Enzymes

A competitive inhibitor with Ki = 0.5 mM and Km = 2 mM is added to an enzyme reaction. What is the apparent Km in presence of this inhibitor at [I] = 1 mM?

A 2 mM

B 4 mM

C 6 mM

D 8 mM

Correct Answer: C. 6 mM

EXPLANATION

Apparent Km = Km(1 + [I]/Ki) = 2(1 + 1/0.5) = 2(1 + 2) = 6 mM. Competitive inhibition increases apparent Km without changing Vmax.

Test

Q.25 Hard Proteins & Enzymes

In a double displacement enzyme reaction mechanism, the enzyme forms a covalent intermediate. Which protease follows this mechanism?

A Pepsin

B Serine proteases

C Metalloproteases

D Cysteine proteases

Correct Answer: B. Serine proteases

EXPLANATION

Serine proteases (like trypsin, chymotrypsin) form an acyl-enzyme intermediate through a nucleophilic attack by the active site serine residue.

Test

Q.26 Hard Proteins & Enzymes

During protein synthesis, a missense mutation changes codon GAA to GUA. Which amino acid substitution occurs?

A Glutamic acid to Valine

B Aspartate to Leucine

C Glutamine to Isoleucine

D Glutamic acid to Alanine

Correct Answer: A. Glutamic acid to Valine

EXPLANATION

GAA codes for Glutamic acid (Glu), GUA codes for Valine (Val). This is a non-conservative substitution of a charged to hydrophobic residue.

Test

Q.27 Hard Proteins & Enzymes

A protein with multiple subunits shows cooperative binding of substrate. This phenomenon is best explained by:

A Competitive inhibition

B Allosteric regulation

C Non-competitive inhibition

D Covalent modification

Correct Answer: B. Allosteric regulation

EXPLANATION

Cooperative binding (positive cooperativity) occurs when binding of one substrate molecule increases affinity for subsequent molecules, a classic example of allosteric regulation as seen in hemoglobin.

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