Q.1 What is the primary function of enzymes in a living cell?
Store genetic information
Catalyze biochemical reactions
Transport oxygen
Maintain cell shape
Explanation - Enzymes act as biological catalysts that increase the rate of chemical reactions without being consumed, allowing vital metabolic processes to occur efficiently.
Correct answer is: Catalyze biochemical reactions
Q.2 Which of the following best describes the term 'substrate'?
The enzyme's active site
The product of the reaction
The molecule upon which an enzyme acts
A type of inhibitor
Explanation - A substrate is the specific reactant that fits into the enzyme's active site to form a product through catalysis.
Correct answer is: The molecule upon which an enzyme acts
Q.3 Which equation represents the Michaelis-Menten relationship for enzyme kinetics?
V = k_cat * [E]
V = (V_max * [S]) / (K_m + [S])
V = (K_m * [S]) / (V_max + [S])
V = k_cat * [S] / (K_m + [E])
Explanation - The Michaelis-Menten equation describes the rate (V) of an enzymatic reaction in terms of maximum velocity (V_max), substrate concentration ([S]), and Michaelis constant (K_m).
Correct answer is: V = (V_max * [S]) / (K_m + [S])
Q.4 A competitive inhibitor increases which of the following parameters?
V_max
K_m
Both V_max and K_m
Neither V_max nor K_m
Explanation - Competitive inhibition increases the apparent K_m (lower affinity) but does not affect V_max, as the inhibitor competes with the substrate for the active site.
Correct answer is: K_m
Q.5 What is the effect of a non-competitive inhibitor on V_max?
No change
Increase
Decrease
It depends on the inhibitor concentration
Explanation - Non-competitive inhibitors bind to an allosteric site, altering enzyme activity and reducing V_max regardless of substrate concentration.
Correct answer is: Decrease
Q.6 Which enzyme type requires a cofactor for its catalytic activity?
Proteases
Lipases
Oxidoreductases
All of the above
Explanation - Many enzymes, including proteases, lipases, and oxidoreductases, need cofactors such as metal ions or organic molecules (e.g., NAD⁺) for activity.
Correct answer is: All of the above
Q.7 Enzyme activity is typically increased by which of the following changes in temperature?
A decrease to 4°C
An increase to 37°C
An increase to 100°C
A decrease to 0°C
Explanation - Most human enzymes function best near body temperature (~37°C); extreme temperatures can denature enzymes.
Correct answer is: An increase to 37°C
Q.8 Which statement best describes enzyme specificity?
Enzymes act on any molecule.
Enzymes act on molecules with a particular shape and chemical properties.
Enzymes act only on DNA.
Enzymes act only on RNA.
Explanation - Enzymes recognize and bind specific substrates based on shape (steric complementarity) and chemical interactions.
Correct answer is: Enzymes act on molecules with a particular shape and chemical properties.
Q.9 What role does the enzyme lactase play in digestion?
Breaks down proteins into amino acids
Breaks down fats into fatty acids
Breaks down lactose into glucose and galactose
Breaks down carbohydrates into monosaccharides
Explanation - Lactase hydrolyzes lactose into simpler sugars that can be absorbed in the small intestine.
Correct answer is: Breaks down lactose into glucose and galactose
Q.10 What is a hallmark of allosteric enzymes?
They have a single substrate binding site.
Their activity is not affected by the presence of other molecules.
They exhibit cooperative binding to substrates.
They are only found in prokaryotes.
Explanation - Allosteric enzymes display cooperative kinetics, often sigmoidal, indicating that substrate binding changes the enzyme's conformation.
Correct answer is: They exhibit cooperative binding to substrates.
Q.11 Which enzyme is most likely to be inhibited by a substrate analog that resembles ATP?
DNA polymerase
RNA polymerase
ATP synthase
All of the above
Explanation - Any enzyme that uses ATP as a cofactor or energy source can be competitively inhibited by an ATP analog.
Correct answer is: All of the above
Q.12 Which of the following is not a factor affecting enzyme kinetics?
Substrate concentration
pH level
Enzyme concentration
Time of day
Explanation - Enzyme activity can be influenced by substrate, pH, temperature, enzyme concentration, and presence of inhibitors, but not directly by circadian rhythms.
Correct answer is: Time of day
Q.13 A mutation that alters the amino acid sequence near an enzyme's active site will most likely:
Increase V_max
Decrease K_m
Decrease substrate affinity
Have no effect
Explanation - Changes in the active site can reduce the binding affinity for the substrate, increasing the apparent K_m.
Correct answer is: Decrease substrate affinity
Q.14 Which of the following best describes the concept of a 'turnover number' (k_cat)?
The number of substrate molecules that bind to an enzyme per minute
The number of enzyme molecules that exist in the cell
The maximum velocity (V_max) of an enzyme
The number of catalytic cycles an enzyme performs per second
Explanation - k_cat represents the catalytic efficiency, indicating how many substrate molecules one enzyme converts to product per unit time.
Correct answer is: The number of catalytic cycles an enzyme performs per second
Q.15 Which type of inhibition is characterized by the inhibitor binding only to the enzyme-substrate complex?
Competitive inhibition
Uncompetitive inhibition
Non-competitive inhibition
Allosteric inhibition
Explanation - Uncompetitive inhibitors bind exclusively to the ES complex, reducing V_max and K_m proportionally.
Correct answer is: Uncompetitive inhibition
Q.16 The 'induced fit' model of enzyme action suggests that:
Enzymes never change shape upon substrate binding
The substrate changes shape to fit the enzyme
Both the enzyme and substrate change conformation upon binding
Enzymes are rigid and cannot adapt
Explanation - Induced fit proposes that binding induces a conformational change in the enzyme to better accommodate the substrate.
Correct answer is: Both the enzyme and substrate change conformation upon binding
Q.17 What is the primary advantage of using a covalent enzyme inhibitor?
It can be easily removed by washing
It permanently deactivates the enzyme
It has no effect on the enzyme's activity
It increases the enzyme's affinity for substrate
Explanation - Covalent inhibitors form irreversible bonds with the enzyme, leading to permanent loss of activity.
Correct answer is: It permanently deactivates the enzyme
Q.18 Which parameter does NOT affect the shape of a Lineweaver-Burk plot?
V_max
K_m
Enzyme concentration
pH of the solution
Explanation - While pH can affect enzyme activity, the Lineweaver-Burk plot shape is determined by V_max, K_m, and enzyme concentration, not the pH per se.
Correct answer is: pH of the solution
Q.19 In the context of enzyme kinetics, what does 'saturation' refer to?
When the enzyme is fully denatured
When substrate concentration is low
When increasing substrate concentration no longer increases reaction rate
When the enzyme is inhibited
Explanation - Saturation occurs when all active sites are occupied; beyond this point, the reaction rate plateaus at V_max.
Correct answer is: When increasing substrate concentration no longer increases reaction rate
Q.20 Which of the following is a classic example of a positive allosteric regulator?
Glucose-6-phosphate
Fructose-1,6-bisphosphate
ATP
AMP
Explanation - Fructose-1,6-bisphosphate activates phosphofructokinase-1, a key regulatory enzyme in glycolysis.
Correct answer is: Fructose-1,6-bisphosphate
Q.21 Which enzyme would you target with a competitive inhibitor to reduce blood clotting?
Thrombin
Factor Xa
Factor VIII
Plasmin
Explanation - Thrombin converts fibrinogen to fibrin; competitive inhibition can reduce clot formation.
Correct answer is: Thrombin
Q.22 Which of the following best describes the term 'Km' in enzyme kinetics?
The maximum rate of reaction
The substrate concentration at which the reaction rate is half of V_max
The rate constant for enzyme synthesis
The number of enzymes per cell
Explanation - K_m indicates the affinity of the enzyme for its substrate; lower K_m means higher affinity.
Correct answer is: The substrate concentration at which the reaction rate is half of V_max
Q.23 A decrease in pH generally leads to:
Increased enzyme activity
Decreased enzyme activity
No change in enzyme activity
Permanent enzyme activation
Explanation - Most enzymes have an optimal pH; deviations often result in reduced activity due to ionization changes.
Correct answer is: Decreased enzyme activity
Q.24 Which of the following statements is TRUE about irreversible inhibitors?
They can be outcompeted by high substrate concentration
They bind reversibly to the active site
They form covalent bonds with the enzyme
They are always competitive inhibitors
Explanation - Irreversible inhibitors typically form covalent bonds, permanently deactivating the enzyme.
Correct answer is: They form covalent bonds with the enzyme
Q.25 In enzyme assays, a sigmoidal curve instead of a hyperbolic one suggests:
The enzyme has multiple identical active sites
The enzyme is inhibited
Cooperative substrate binding
The substrate is unstable
Explanation - Sigmoidal kinetics often result from cooperative binding, seen in allosteric enzymes.
Correct answer is: Cooperative substrate binding
Q.26 Which of the following would most likely increase the K_m of an enzyme?
Increasing enzyme concentration
Adding a competitive inhibitor
Changing the temperature to optimum
Reducing the pH to optimum
Explanation - Competitive inhibitors increase the apparent K_m by requiring higher substrate concentrations to achieve the same rate.
Correct answer is: Adding a competitive inhibitor
Q.27 Which type of enzyme catalyzes the transfer of a functional group from one molecule to another?
Transferases
Hydrolases
Ligases
Oxidoreductases
Explanation - Transferases move functional groups such as methyl or phosphate groups between substrates.
Correct answer is: Transferases
Q.28 The term 'catalytic efficiency' (k_cat/K_m) indicates:
The maximum rate of reaction
The enzyme's turnover number
The ratio of catalytic speed to substrate affinity
The enzyme's concentration in the cell
Explanation - Catalytic efficiency combines both how fast an enzyme works and how well it binds its substrate.
Correct answer is: The ratio of catalytic speed to substrate affinity
Q.29 Which of the following enzymes is involved in the final step of the citric acid cycle?
Citrate synthase
Isocitrate dehydrogenase
Aconitase
Succinate dehydrogenase
Explanation - Succinate dehydrogenase oxidizes succinate to fumarate in the citric acid cycle.
Correct answer is: Succinate dehydrogenase
Q.30 Why are enzymes often stored in inactive forms in cells?
To prevent accidental denaturation
To reduce the energy cost of synthesis
To avoid premature or uncontrolled reactions
Because they are unstable in active form
Explanation - Inactive forms (zymogens) prevent enzymes from reacting before they reach their intended site.
Correct answer is: To avoid premature or uncontrolled reactions
Q.31 Which of the following best describes the effect of an allosteric activator?
Increases V_max
Decreases K_m
Both increases V_max and decreases K_m
Both decreases V_max and increases K_m
Explanation - Allosteric activators often enhance enzyme activity and increase substrate affinity, raising V_max and lowering K_m.
Correct answer is: Both increases V_max and decreases K_m
Q.32 An enzyme that catalyzes the hydrolysis of a peptide bond between amino acids is a:
Lipase
Protease
Phosphatase
Ligase
Explanation - Proteases (also called peptidases) break peptide bonds in proteins.
Correct answer is: Protease
Q.33 Which of the following would be expected if an enzyme is inhibited by a non-competitive inhibitor and substrate concentration is increased?
V_max increases, K_m unchanged
V_max unchanged, K_m increases
V_max decreases, K_m unchanged
Both V_max and K_m increase
Explanation - Non-competitive inhibition lowers the maximum rate without affecting substrate affinity, so K_m stays the same.
Correct answer is: V_max decreases, K_m unchanged
Q.34 Which enzyme uses ATP as a cofactor to phosphorylate glucose during glycolysis?
Hexokinase
Phosphofructokinase-1
Pyruvate kinase
Glycogen phosphorylase
Explanation - PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, using ATP.
Correct answer is: Phosphofructokinase-1
Q.35 A decrease in the V_max of an enzyme due to a mutation that alters its active site is most likely caused by:
An increase in substrate affinity
A reduction in the number of active enzymes
A shift in the enzyme's optimal pH
An increase in K_m
Explanation - A mutation may impair catalytic function, effectively lowering V_max by reducing the proportion of active enzyme.
Correct answer is: A reduction in the number of active enzymes
Q.36 The 'Hill coefficient' in enzyme kinetics indicates:
The number of active sites on the enzyme
The cooperativity of substrate binding
The enzyme's molecular weight
The reaction's equilibrium constant
Explanation - A Hill coefficient >1 indicates positive cooperativity; <1 indicates negative cooperativity.
Correct answer is: The cooperativity of substrate binding
Q.37 Which of the following enzymes is most relevant in the synthesis of ATP during cellular respiration?
Hexokinase
ATP synthase
Cytochrome c oxidase
Lactate dehydrogenase
Explanation - ATP synthase uses the proton gradient to produce ATP from ADP and inorganic phosphate.
Correct answer is: ATP synthase
Q.38 Which factor will most directly increase the catalytic efficiency (k_cat/K_m) of an enzyme?
Decrease substrate affinity
Increase k_cat
Increase K_m
Reduce enzyme concentration
Explanation - Catalytic efficiency increases with higher turnover number or lower K_m; raising k_cat directly boosts efficiency.
Correct answer is: Increase k_cat
Q.39 Which type of enzyme catalyzes the addition of a phosphate group to a substrate using ATP as the phosphate donor?
Kinase
Phosphatase
Ligase
Transaminase
Explanation - Kinases transfer a phosphate group from ATP to a substrate, often regulating enzyme activity.
Correct answer is: Kinase
Q.40 Which of the following statements about enzyme inhibitors is FALSE?
Competitive inhibitors bind to the active site
Non-competitive inhibitors bind to an allosteric site
Allosteric inhibitors can be activators as well
Inhibitors never form covalent bonds with enzymes
Explanation - Some inhibitors, like suicide inhibitors, form covalent bonds and irreversibly inhibit enzymes.
Correct answer is: Inhibitors never form covalent bonds with enzymes
Q.41 What is the effect of an irreversible inhibitor on the Michaelis constant (K_m)?
It increases
It decreases
It remains unchanged
It becomes undefined
Explanation - Irreversible inhibitors reduce the effective enzyme concentration, affecting V_max, but do not change substrate affinity (K_m).
Correct answer is: It remains unchanged
Q.42 Which of the following enzymes is a key regulator of glycogen synthesis?
Glycogen phosphorylase
Glycogen synthase
Phosphoglucomutase
Hexokinase
Explanation - Glycogen synthase adds glucose units to the glycogen chain during glycogenesis.
Correct answer is: Glycogen synthase
Q.43 Which of the following would likely increase the rate of an enzyme-catalyzed reaction?
Higher enzyme concentration
Lower substrate concentration
A competitive inhibitor
A temperature below optimal
Explanation - Increasing the amount of enzyme increases the number of active sites available for catalysis, raising reaction rate.
Correct answer is: Higher enzyme concentration
Q.44 An enzyme that uses water to break a chemical bond is called a:
Ligase
Hydrolase
Oxidoreductase
Transferase
Explanation - Hydrolases catalyze the hydrolysis of bonds using water as a reactant.
Correct answer is: Hydrolase
Q.45 Which of the following statements is true regarding enzyme denaturation?
Denaturation always increases enzyme activity.
Denaturation can be reversed by adding more substrate.
Denaturation involves the loss of tertiary structure.
Denaturation is the same as catalysis.
Explanation - Denaturation disrupts the enzyme's 3D structure, often inactivating it.
Correct answer is: Denaturation involves the loss of tertiary structure.
Q.46 A decrease in the temperature of an enzymatic reaction typically results in:
An increase in reaction rate
No change in reaction rate
A decrease in reaction rate
Immediate enzyme activation
Explanation - Lower temperatures reduce molecular collisions, slowing the rate of reaction.
Correct answer is: A decrease in reaction rate
Q.47 Which of the following is NOT a type of enzyme classification?
Oxidoreductases
Transferases
Ligases
Chromatases
Explanation - Chromatases is not a recognized enzyme class; the six major classes are oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
Correct answer is: Chromatases
Q.48 Which of the following best describes a 'zymogen'?
An enzyme that is always active
An inactive precursor of an enzyme
An enzyme that binds DNA
An enzyme that requires light
Explanation - Zymogens are inactive enzyme precursors activated by cleavage.
Correct answer is: An inactive precursor of an enzyme
Q.49 The ratio of k_cat to K_m is often used as a measure of:
Enzyme concentration
Enzyme specificity
Catalytic efficiency
Substrate concentration
Explanation - k_cat/K_m reflects how efficiently an enzyme converts substrate to product at low substrate concentrations.
Correct answer is: Catalytic efficiency
Q.50 Which of the following best explains why enzymes have a 'turnover number' of 1000 per second?
The enzyme is extremely unstable
The enzyme can convert one substrate molecule each second
The enzyme can convert 1000 substrate molecules per second
The enzyme can bind 1000 substrates at once
Explanation - Turnover number (k_cat) of 1000 s⁻¹ indicates each enzyme molecule processes 1000 substrates per second.
Correct answer is: The enzyme can convert 1000 substrate molecules per second
Q.51 Which of the following enzyme classes is responsible for breaking down complex polysaccharides in the gut?
Proteases
Lipases
Amylases
Ligases
Explanation - Amylases hydrolyze starch, a complex carbohydrate, into simpler sugars.
Correct answer is: Amylases
Q.52 Which of the following best describes the 'Michaelis constant' (K_m) as a measure of enzyme activity?
The rate of the reaction at saturation
The substrate concentration required to reach half-maximal velocity
The enzyme's molecular weight
The number of active sites on an enzyme
Explanation - K_m indicates how tightly the enzyme binds its substrate: lower K_m means higher affinity.
Correct answer is: The substrate concentration required to reach half-maximal velocity
Q.53 Which of the following would be classified as a 'coenzyme'?
ATP
Magnesium ion
DNA
Hemoglobin
Explanation - Coenzymes are organic non-protein molecules that assist enzymes, like ATP providing a phosphate group.
Correct answer is: ATP
Q.54 A drug that selectively inhibits a viral protease to prevent viral replication is an example of:
A non-competitive inhibitor
A competitive inhibitor
An uncompetitive inhibitor
All of the above
Explanation - Many antiviral drugs mimic the protease's substrate and compete for the active site.
Correct answer is: A competitive inhibitor
Q.55 Which parameter would NOT be altered by an increase in enzyme concentration?
V_max
K_m
Reaction rate at low substrate concentration
Overall reaction time
Explanation - Enzyme concentration affects V_max but not substrate affinity (K_m).
Correct answer is: K_m
Q.56 In a Lineweaver-Burk plot, the slope is equal to:
V_max
K_m
K_m/V_max
V_max/K_m
Explanation - The slope of the double reciprocal plot (1/V vs. 1/[S]) is K_m/V_max.
Correct answer is: K_m/V_max
Q.57 Which of the following would result in a 'shifted' Michaelis-Menten curve to the right?
Increased enzyme concentration
A competitive inhibitor present
A non-competitive inhibitor present
Lower temperature
Explanation - A competitive inhibitor raises apparent K_m, shifting the curve to the right while V_max remains unchanged.
Correct answer is: A competitive inhibitor present
Q.58 Which enzyme would you target to reduce the synthesis of fatty acids in a bacterial cell?
Acetyl-CoA carboxylase
DNA gyrase
RNA polymerase
Peptidoglycan synthase
Explanation - Acetyl-CoA carboxylase catalyzes the first committed step in fatty acid biosynthesis.
Correct answer is: Acetyl-CoA carboxylase
Q.59 The term 'substrate inhibition' describes:
Inhibition that occurs only at low substrate concentrations
Inhibition that occurs at high substrate concentrations
Inhibition that is reversed by adding more substrate
Inhibition that is irreversible
Explanation - In substrate inhibition, excess substrate binds an additional site, reducing enzyme activity.
Correct answer is: Inhibition that occurs at high substrate concentrations
Q.60 Which of the following statements about the 'enzyme-substrate complex (ES)' is FALSE?
It is a transient intermediate
It is required for product formation
It has higher free energy than the reactants
It can form in the presence of inhibitors
Explanation - The ES complex typically has lower free energy than the separated reactants, making its formation favorable.
Correct answer is: It has higher free energy than the reactants
Q.61 Which of the following would most likely decrease the rate of a catalyzed reaction?
Addition of a cofactor
An increase in pH outside the optimal range
Increased enzyme concentration
Use of a more efficient substrate analogue
Explanation - Deviation from optimal pH can destabilize the enzyme and reduce its activity.
Correct answer is: An increase in pH outside the optimal range
Q.62 Which of the following enzymes is primarily responsible for repairing DNA double-strand breaks?
DNA ligase
DNA polymerase
DNA topoisomerase
DNA repair endonuclease
Explanation - DNA repair endonucleases recognize and cleave damaged DNA strands, facilitating repair.
Correct answer is: DNA repair endonuclease
Q.63 A mutation that changes a key catalytic residue in an enzyme will most likely:
Increase V_max
Decrease K_m
Decrease both V_max and K_m
Have no effect on enzyme kinetics
Explanation - A catalytic residue mutation often impairs both binding and turnover, lowering V_max and increasing K_m.
Correct answer is: Decrease both V_max and K_m
Q.64 Which of the following is a typical function of the enzyme urease?
Breakdown of urea into ammonia and carbon dioxide
Phosphorylation of glucose
Synthesis of fatty acids
Replication of DNA
Explanation - Urease catalyzes the hydrolysis of urea, producing ammonia and CO₂, vital for nitrogen metabolism.
Correct answer is: Breakdown of urea into ammonia and carbon dioxide
Q.65 Which enzyme is directly involved in the conversion of pyruvate to acetyl-CoA during aerobic respiration?
Pyruvate dehydrogenase
Cytochrome c
Succinate dehydrogenase
Glutamate dehydrogenase
Explanation - Pyruvate dehydrogenase complex oxidatively decarboxylates pyruvate to acetyl-CoA, feeding the TCA cycle.
Correct answer is: Pyruvate dehydrogenase
Q.66 Enzymes that facilitate the transfer of a single electron from a donor to an acceptor are classified as:
Oxidoreductases
Hydrolases
Lyases
Isomerases
Explanation - Oxidoreductases mediate oxidation-reduction reactions, moving electrons between molecules.
Correct answer is: Oxidoreductases
Q.67 Which of the following best describes the 'thermodynamic efficiency' of an enzyme-catalyzed reaction?
The ratio of product to substrate concentrations at equilibrium
The ability of the enzyme to lower the activation energy
The speed at which the enzyme converts substrate to product
The concentration of enzyme needed for maximum activity
Explanation - Enzymes are not thermodynamically efficient in energy terms but thermodynamically favorable; they lower activation energy to increase reaction rates.
Correct answer is: The ability of the enzyme to lower the activation energy
Q.68 Which of the following is an example of an 'allosteric inhibitor'?
Glucose
Fructose-1,6-bisphosphate
ATP
AMP
Explanation - ATP can bind allosterically to enzymes like phosphofructokinase-1, inhibiting their activity.
Correct answer is: ATP
Q.69 Which of the following is a characteristic of an irreversible inhibitor?
It can be displaced by high substrate concentration
It binds non-covalently to the enzyme
It permanently inactivates the enzyme
It is a type of competitive inhibitor
Explanation - Irreversible inhibitors typically form covalent bonds, resulting in permanent loss of enzyme activity.
Correct answer is: It permanently inactivates the enzyme
Q.70 A low K_m value for an enzyme indicates:
High substrate concentration is needed for activity
Low affinity for substrate
High affinity for substrate
The enzyme is inactive
Explanation - A small K_m means the enzyme binds its substrate tightly, requiring less substrate for half-maximal activity.
Correct answer is: High affinity for substrate
Q.71 The process of converting a monomer into a polymer using an enzyme is known as:
Catabolism
Anabolism
Polymerization
Degradation
Explanation - Enzymes like DNA polymerase or RNA polymerase add nucleotides to form long chains (polymers).
Correct answer is: Polymerization
Q.72 Which of the following is NOT typically considered an enzyme?
DNA polymerase
ATP synthase
Hemoglobin
Lipase
Explanation - Hemoglobin transports oxygen but does not catalyze reactions, unlike the listed enzymes.
Correct answer is: Hemoglobin
Q.73 Which of the following best explains the term 'kcat' in enzyme kinetics?
The equilibrium constant for the enzyme-substrate interaction
The number of enzyme molecules per cell
The turnover number, indicating how many substrate molecules one enzyme converts per second
The ratio of substrate concentration to enzyme concentration
Explanation - kcat is the maximum number of substrate molecules processed by an enzyme per second at saturation.
Correct answer is: The turnover number, indicating how many substrate molecules one enzyme converts per second
Q.74 Which enzyme class catalyzes the addition of a new phosphate group to a substrate?
Kinase
Phosphatase
Ligase
Isomerase
Explanation - Kinases transfer a phosphate group from ATP to a substrate, often regulating biological processes.
Correct answer is: Kinase
Q.75 An enzyme that breaks down a polysaccharide into monomeric sugars is a:
Protease
Amylase
Lipase
Ligase
Explanation - Amylases hydrolyze starch (a polysaccharide) into glucose or maltose units.
Correct answer is: Amylase
Q.76 Which of the following statements about the 'substrate inhibition' phenomenon is correct?
It occurs only at low substrate concentrations
It results in a linear relationship between velocity and substrate concentration
It is characterized by a decrease in reaction velocity at high substrate concentrations
It is caused by product accumulation
Explanation - In substrate inhibition, excess substrate binds to an additional site, reducing the catalytic activity.
Correct answer is: It is characterized by a decrease in reaction velocity at high substrate concentrations
Q.77 Which of the following best describes the concept of enzyme cooperativity?
Enzymes bind substrates independently
Enzymes have identical active sites
Binding of substrate to one site affects binding at another site
Enzymes do not exhibit sigmoidal kinetics
Explanation - Cooperativity refers to the influence of substrate binding at one site on the affinity at other sites, leading to sigmoidal kinetics.
Correct answer is: Binding of substrate to one site affects binding at another site
Q.78 Which of the following best explains why enzyme activity can be altered by changing the ionic strength of the solution?
It changes the enzyme's genetic code
It modifies the pH of the solution
It influences electrostatic interactions within the enzyme
It directly changes the enzyme's tertiary structure
Explanation - Ionic strength can shield or enhance charges, affecting enzyme conformation and substrate binding.
Correct answer is: It influences electrostatic interactions within the enzyme
Q.79 Which enzyme would be targeted to treat hypercholesterolemia by preventing the synthesis of cholesterol?
HMG-CoA reductase
HMG-CoA synthase
Acetyl-CoA carboxylase
ATP citrate lyase
Explanation - HMG-CoA reductase catalyzes the rate-limiting step in cholesterol biosynthesis; statins inhibit this enzyme.
Correct answer is: HMG-CoA reductase
Q.80 Which of the following describes a 'feedback inhibitor'?
An inhibitor that binds only to the enzyme-substrate complex
An inhibitor that signals the end product to reduce its own synthesis
An inhibitor that irreversibly binds the active site
An inhibitor that is a product of the reaction but does not affect the enzyme
Explanation - Feedback inhibition occurs when the end product of a pathway inhibits an early enzyme, preventing overproduction.
Correct answer is: An inhibitor that signals the end product to reduce its own synthesis
Q.81 Which of the following enzyme classes is responsible for the cleavage of glycosidic bonds in complex sugars?
Hydrolases
Transferases
Oxidoreductases
Isomerases
Explanation - Hydrolases, such as glycosidases, catalyze the hydrolysis of glycosidic bonds.
Correct answer is: Hydrolases
Q.82 A mutation in the catalytic triad of a serine protease will most likely:
Increase enzymatic activity
Decrease substrate affinity but maintain turnover
Significantly reduce or abolish enzyme activity
Have no effect on the enzyme's function
Explanation - The catalytic triad is essential for protease activity; mutating it disrupts catalysis.
Correct answer is: Significantly reduce or abolish enzyme activity
Q.83 Which of the following best describes the 'turnover number' (kcat) in terms of enzyme kinetics?
The number of enzymes in a cell
The number of substrate molecules processed per second per enzyme
The concentration of substrate at which the reaction rate is half-maximal
The maximum velocity of the enzyme
Explanation - kcat expresses the catalytic speed of an enzyme, indicating how many molecules it converts per unit time.
Correct answer is: The number of substrate molecules processed per second per enzyme
Q.84 Which of the following enzymes is crucial for the initial step of glycolysis?
Hexokinase
Phosphofructokinase-1
Pyruvate kinase
Glyceraldehyde-3-phosphate dehydrogenase
Explanation - Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate, committing it to glycolysis.
Correct answer is: Hexokinase
Q.85 In enzyme kinetics, which parameter is directly proportional to enzyme concentration?
V_max
K_m
k_cat
Reaction rate at saturating substrate
Explanation - V_max increases linearly with enzyme concentration; K_m and k_cat are independent of enzyme amount.
Correct answer is: V_max
Q.86 Which of the following best illustrates the concept of 'enzyme-substrate complex stability'?
High activation energy
Low free energy of the ES complex
High K_m value
Low k_cat value
Explanation - A stable ES complex has lower free energy, facilitating the conversion to product.
Correct answer is: Low free energy of the ES complex
Q.87 Which enzyme class catalyzes the removal of phosphate groups from substrates?
Phosphatases
Kinases
Ligases
Isomerases
Explanation - Phosphatases catalyze the hydrolysis of phosphate esters, removing phosphate groups.
Correct answer is: Phosphatases
Q.88 The 'Michaelis-Menten constant' (K_m) can be interpreted as:
The rate at which an enzyme is produced
The concentration of substrate at which the enzyme is half-occupied
The maximum velocity of the enzyme
The total amount of enzyme present in the cell
Explanation - K_m approximates the substrate concentration needed for half-maximal activity, reflecting affinity.
Correct answer is: The concentration of substrate at which the enzyme is half-occupied
Q.89 Which of the following is a key difference between an enzyme and a catalyst in chemistry?
Enzymes are proteins; chemical catalysts are not
Enzymes are consumed in the reaction
Enzymes can be regulated by cellular signals
Chemical catalysts cannot be regenerated
Explanation - Enzymes can be regulated by various mechanisms (allostery, covalent modification) within living cells.
Correct answer is: Enzymes can be regulated by cellular signals
Q.90 Which of the following enzymes is responsible for the synthesis of the DNA double helix during replication?
DNA polymerase
DNA ligase
RNA polymerase
Topoisomerase
Explanation - DNA polymerase catalyzes the addition of nucleotides to synthesize a new DNA strand.
Correct answer is: DNA polymerase
Q.91 Which of the following would most likely be an example of a non-competitive inhibitor?
An ATP analog that binds to the active site
A molecule that binds only to the ES complex
A molecule that binds to an allosteric site
A substrate analog that competes for the active site
Explanation - Non-competitive inhibitors bind to an allosteric site, affecting enzyme activity regardless of substrate concentration.
Correct answer is: A molecule that binds to an allosteric site
Q.92 Which of the following best describes a 'zinc-binding enzyme'?
An enzyme that uses zinc as a structural cofactor
An enzyme that releases zinc ions during catalysis
An enzyme that transports zinc across membranes
An enzyme that synthesizes zinc from metal ions
Explanation - Zinc-binding enzymes often rely on zinc ions for structural stability or catalytic function.
Correct answer is: An enzyme that uses zinc as a structural cofactor
Q.93 Which of the following enzymes is a key component of the electron transport chain?
Cytochrome c oxidase
Cytochrome c peroxidase
Cytochrome c phosphatase
Cytochrome c kinase
Explanation - Cytochrome c oxidase (complex IV) transfers electrons to oxygen in the mitochondrial electron transport chain.
Correct answer is: Cytochrome c oxidase
Q.94 A mutation that causes a 'gain of function' in an enzyme will most likely:
Increase the enzyme's affinity for its substrate
Decrease enzyme activity
Increase the enzyme's K_m
Inactivate the enzyme
Explanation - Gain-of-function mutations often enhance enzyme activity or substrate binding, leading to increased catalytic efficiency.
Correct answer is: Increase the enzyme's affinity for its substrate
Q.95 Which of the following best characterizes 'enzyme kinetics'?
The study of enzyme structure only
The study of how enzyme activity changes with temperature and pH
The study of enzyme-mediated reaction rates under various conditions
The study of enzyme gene expression
Explanation - Enzyme kinetics focuses on measuring reaction rates to understand enzyme behavior under different conditions.
Correct answer is: The study of enzyme-mediated reaction rates under various conditions
Q.96 Which of the following best describes the role of a 'coenzyme' in enzyme catalysis?
It permanently inactivates the enzyme
It acts as a substrate for the reaction
It assists the enzyme by donating or accepting chemical groups
It is a component of the enzyme's active site that is never released
Explanation - Coenzymes are small organic molecules that shuttle electrons or functional groups during enzyme-catalyzed reactions.
Correct answer is: It assists the enzyme by donating or accepting chemical groups
Q.97 Which enzyme is involved in the hydrolysis of the peptide bond in the bacterial cell wall?
Peptidoglycan hydrolase
Chitinase
Lipase
Lactase
Explanation - Peptidoglycan hydrolases (amidases, endopeptidases) degrade bacterial cell walls during growth or lysis.
Correct answer is: Peptidoglycan hydrolase
Q.98 Which of the following statements about 'enzyme activation' is FALSE?
It can occur via covalent modification
It always involves a change in the enzyme's primary structure
Allosteric changes can activate enzymes
Substrate binding can activate some enzymes
Explanation - Enzyme activation often involves conformational changes or post-translational modifications, not changes to primary sequence.
Correct answer is: It always involves a change in the enzyme's primary structure
Q.99 Which of the following best explains why enzymes are considered 'specific'?
They can catalyze any reaction if the temperature is high enough
They only bind to a single substrate or a narrow set of substrates
They are not affected by inhibitors
They are composed only of amino acids
Explanation - Enzyme specificity refers to the precise recognition of a particular substrate or group of substrates.
Correct answer is: They only bind to a single substrate or a narrow set of substrates
Q.100 Which of the following best describes the effect of a non-competitive inhibitor on the Michaelis-Menten equation?
It increases the apparent K_m
It increases the apparent V_max
It decreases the apparent V_max but K_m remains unchanged
It decreases both V_max and K_m equally
Explanation - Non-competitive inhibition reduces the overall maximum rate while leaving substrate affinity unaffected.
Correct answer is: It decreases the apparent V_max but K_m remains unchanged
Q.101 Which of the following enzymes is responsible for the removal of the terminal phosphate from ATP during phosphorylation reactions?
ATPase
ATP synthase
Kinase
Phosphatase
Explanation - Phosphatases catalyze the removal (dephosphorylation) of phosphate groups from substrates, often including ATP.
Correct answer is: Phosphatase
Q.102 Which of the following best defines 'enzyme catalysis'?
The enzyme is consumed during the reaction
The enzyme changes the equilibrium position of the reaction
The enzyme lowers the activation energy of a reaction
The enzyme increases the thermodynamic stability of the products
Explanation - Enzymes function by stabilizing the transition state, reducing the activation energy required for a reaction.
Correct answer is: The enzyme lowers the activation energy of a reaction