Home Subjects Biochemistry Proteins & Enzymes

Biochemistry
Proteins & Enzymes

Metabolic pathways, enzymes, proteins

100 Q 3 Topics Take Test
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Difficulty: All Easy Medium Hard 91–100 of 100
Topics in Biochemistry
All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78
Q.91 Medium Proteins & Enzymes
Which amino acid sequence contains a hydrophobic amino acid that is commonly found in the hydrophobic core of proteins?
A Ser-Asp-Glu
B Leu-Ile-Val
C Lys-Arg-His
D Thr-Ser-Cys
Correct Answer:  B. Leu-Ile-Val
EXPLANATION

Leucine, Isoleucine, and Valine are branched-chain hydrophobic amino acids typically buried in the interior of folded proteins.

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Q.92 Medium Proteins & Enzymes
Denaturation of proteins can be caused by all EXCEPT:
A High temperature
B Extreme pH
C Organic solvents
D Peptide bond formation
Correct Answer:  D. Peptide bond formation
EXPLANATION

Peptide bond formation is part of protein synthesis and structure, not denaturation. Denaturation involves disruption of secondary and tertiary structures.

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Q.93 Medium Proteins & Enzymes
Which type of enzyme inhibition is characterized by a competitive interaction with the active site?
A Non-competitive inhibition
B Uncompetitive inhibition
C Allosteric inhibition
D Competitive inhibition
Correct Answer:  D. Competitive inhibition
EXPLANATION

In competitive inhibition, the inhibitor competes with substrate for the active site and can be overcome by increasing substrate concentration.

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Q.94 Medium Proteins & Enzymes
The Michaelis-Menten equation describes enzyme kinetics. What does Km represent?
A Maximum velocity of the enzyme
B Substrate concentration at half maximal velocity
C Enzyme concentration
D Catalytic constant
Correct Answer:  B. Substrate concentration at half maximal velocity
EXPLANATION

Km (Michaelis constant) represents the substrate concentration at which enzyme velocity is half of Vmax, indicating substrate affinity.

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Q.95 Medium Proteins & Enzymes
Enzyme cofactors are non-protein substances that are essential for enzyme activity. Which of the following is NOT a cofactor?
A Metal ions like Zn²⁺
B Coenzyme A
C NAD⁺
D Serine
Correct Answer:  D. Serine
EXPLANATION

Serine is an amino acid, not a cofactor. Cofactors include metal ions and coenzymes like NAD⁺, FAD, and CoA.

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Which of the following is an example of a globular protein?
A Collagen
B Keratin
C Hemoglobin
D Elastin
Correct Answer:  C. Hemoglobin
EXPLANATION

Hemoglobin is a globular protein with a compact, spherical structure, unlike fibrous proteins like collagen and keratin.

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Isoelectric point (pI) of a protein is defined as the pH at which:
A Protein is maximally soluble
B Net charge on the protein is zero
C Protein denatures completely
D Enzyme activity is maximum
Correct Answer:  B. Net charge on the protein is zero
EXPLANATION

At isoelectric point, the number of positive charges equals negative charges, resulting in zero net charge and minimum solubility.

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Which enzyme catalyzes the hydrolysis of peptide bonds from the C-terminal end?
A Pepsin
B Carboxypeptidase
C Endopeptidase
D Aminopeptidase
Correct Answer:  B. Carboxypeptidase
EXPLANATION

Carboxypeptidase is an exopeptidase that removes amino acids sequentially from the C-terminal end of proteins.

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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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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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