Showing 271–278 of 278 questions
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.
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.
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.
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.
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.
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.
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.
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.
