Q.1 Which of the following is a characteristic property of enzymes?
They increase the activation energy
They are consumed in reactions
They are highly specific
They change the equilibrium constant
Explanation - Enzymes are highly specific to their substrates and catalyze reactions without being consumed. They do not change the equilibrium constant but lower the activation energy.
Correct answer is: They are highly specific
Q.2 The active site of an enzyme is:
Where the substrate binds
Where the enzyme is synthesized
The site of enzyme denaturation
The regulatory site of enzyme activity
Explanation - The active site is a specific region of an enzyme where the substrate binds and undergoes a chemical reaction.
Correct answer is: Where the substrate binds
Q.3 Which type of enzyme catalyzes oxidation-reduction reactions?
Transferases
Oxidoreductases
Hydrolases
Lyases
Explanation - Oxidoreductases catalyze redox reactions, transferring electrons from one molecule to another.
Correct answer is: Oxidoreductases
Q.4 An enzyme that requires a non-protein component for activity is called:
A holoenzyme
An apoenzyme
A coenzyme
An inhibitor
Explanation - A holoenzyme is the active form of an enzyme consisting of the apoenzyme (protein part) and its cofactor (non-protein component).
Correct answer is: A holoenzyme
Q.5 Which of the following is a cofactor required by many enzymes for activity?
Vitamin D
Magnesium ion
Glucose
Cholesterol
Explanation - Magnesium ions often serve as cofactors that assist enzymes in catalysis by stabilizing charges.
Correct answer is: Magnesium ion
Q.6 The Michaelis-Menten constant (Km) represents:
Substrate concentration at half-maximal velocity
Maximum enzyme velocity
Enzyme concentration
Rate of product formation at zero substrate
Explanation - Km is the substrate concentration at which the reaction velocity is half of Vmax and is a measure of enzyme affinity for its substrate.
Correct answer is: Substrate concentration at half-maximal velocity
Q.7 Which type of inhibition can be overcome by increasing substrate concentration?
Competitive inhibition
Non-competitive inhibition
Uncompetitive inhibition
Allosteric inhibition
Explanation - In competitive inhibition, the inhibitor competes with the substrate for the active site; increasing substrate can outcompete the inhibitor.
Correct answer is: Competitive inhibition
Q.8 Enzymes that break down proteins into smaller peptides are called:
Lipases
Proteases
Amylases
Ligases
Explanation - Proteases are enzymes that catalyze the hydrolysis of peptide bonds in proteins.
Correct answer is: Proteases
Q.9 Which of the following factors does NOT affect enzyme activity?
pH
Temperature
Substrate concentration
Molecular weight of substrate
Explanation - Enzyme activity depends on pH, temperature, and substrate concentration, but the molecular weight of substrate alone does not directly affect enzyme activity.
Correct answer is: Molecular weight of substrate
Q.10 Allosteric enzymes are regulated by:
Competitive inhibitors only
Substrate binding only
Effectors binding at regulatory sites
Temperature changes
Explanation - Allosteric enzymes have regulatory sites where effectors (activators or inhibitors) bind, altering enzyme activity.
Correct answer is: Effectors binding at regulatory sites
Q.11 Which enzyme class adds water to break bonds?
Hydrolases
Ligases
Oxidoreductases
Isomerases
Explanation - Hydrolases catalyze hydrolysis reactions, breaking chemical bonds by the addition of water.
Correct answer is: Hydrolases
Q.12 Which of the following is a ribozyme?
DNA polymerase
Peptidyl transferase of ribosome
Amylase
Lipase
Explanation - Ribozymes are RNA molecules with catalytic activity; the peptidyl transferase of the ribosome is an RNA enzyme catalyzing peptide bond formation.
Correct answer is: Peptidyl transferase of ribosome
Q.13 Enzyme activity can be measured by:
Change in substrate concentration
Change in product concentration
Change in reaction rate
All of the above
Explanation - Enzyme activity is often measured by monitoring the decrease in substrate, increase in product, or overall reaction rate.
Correct answer is: All of the above
Q.14 Which type of enzyme inhibition is irreversible?
Competitive
Non-competitive
Suicide inhibition
Allosteric
Explanation - Suicide inhibitors bind permanently to the enzyme and inactivate it irreversibly.
Correct answer is: Suicide inhibition
Q.15 Zymogens are:
Active enzymes
Inactive enzyme precursors
Allosteric inhibitors
Cofactors
Explanation - Zymogens are inactive precursors of enzymes that require a biochemical change to become active.
Correct answer is: Inactive enzyme precursors
Q.16 Which of the following enzymes catalyzes the joining of two molecules using ATP?
Ligases
Hydrolases
Transferases
Lyases
Explanation - Ligases catalyze the formation of covalent bonds between molecules using energy from ATP.
Correct answer is: Ligases
Q.17 Enzyme denaturation can occur due to:
High temperature
Extreme pH
Heavy metal ions
All of the above
Explanation - Enzymes can lose their three-dimensional structure and activity due to heat, pH extremes, or binding of heavy metals.
Correct answer is: All of the above
Q.18 Which type of enzyme catalyzes the transfer of functional groups?
Transferases
Hydrolases
Lyases
Oxidoreductases
Explanation - Transferases catalyze the transfer of functional groups such as methyl, phosphate, or amino groups from one molecule to another.
Correct answer is: Transferases
Q.19 An enzyme that catalyzes the rearrangement of atoms within a molecule is classified as:
Isomerase
Lyase
Ligase
Oxidoreductase
Explanation - Isomerases catalyze structural rearrangements within a molecule to form isomers.
Correct answer is: Isomerase
Q.20 The Lineweaver-Burk plot is a:
Double reciprocal plot
Logarithmic plot
Enzyme-substrate complex graph
Temperature vs activity graph
Explanation - The Lineweaver-Burk plot is a double reciprocal plot (1/V vs 1/[S]) used to determine Km and Vmax.
Correct answer is: Double reciprocal plot
Q.21 Which factor stabilizes the enzyme-substrate complex?
Hydrogen bonds
Ionic interactions
Hydrophobic interactions
All of the above
Explanation - Multiple non-covalent interactions such as hydrogen bonds, ionic interactions, and hydrophobic forces stabilize the enzyme-substrate complex.
Correct answer is: All of the above
Q.22 Enzyme specificity is best explained by:
Lock and key model
Induced fit model
Both models
None of the above
Explanation - Enzyme specificity can be described by the lock-and-key model (perfect fit) and induced fit model (enzyme changes shape slightly upon substrate binding).
Correct answer is: Both models
Q.23 Which of the following is an example of a digestive enzyme?
Pepsin
Hexokinase
DNA polymerase
ATP synthase
Explanation - Pepsin is a protease found in the stomach that digests proteins into peptides.
Correct answer is: Pepsin
Q.24 Enzyme activity units are usually expressed in terms of:
Amount of substrate converted per unit time
Amount of enzyme present
Temperature
pH
Explanation - Enzyme activity is measured by how much substrate is converted into product per unit time under defined conditions.
Correct answer is: Amount of substrate converted per unit time
Q.25 Which enzyme is responsible for breaking down starch into maltose?
Amylase
Lipase
Protease
Cellulase
Explanation - Amylase catalyzes the hydrolysis of starch into maltose units.
Correct answer is: Amylase