Set of Important MCQs on Enzymes for the preparation of tests for chemistry and biology.
Aldolase belongs to ________ class of enzymes.
- Transferases
- Lyases
- Hydrolases
- Isomerases
Question’s Answer: Lyases
All of the following enzymes show group specificity, excluding
- Hexokinase
- Glucokinase
- Phospholipase
- Amino acid oxidase
Question’s Answer: Glucokinase
Pyruvate carboxylase belongs to ________ class of enzymes.
- Ligase
- Oxidoreductasec
- Transferase
- Hydrolase
Question’s Answer: Ligase
The co-enzymes have which properties?
- Having the same quaternary structures like the enzymes
- Structural analogues of enzymes
- Soluble, colloidal, protein molecules
- Heat stable, dialyzable, non-protein organic molecules
Question’s Answer: Heat stable, dialyzable, non-protein organic molecules
When substrate concentration is equal to Km of an enzyme:
- Half of the enzyme molecules are bound to the substrate
- The velocity of the reaction is = V
- The enzyme is saturated with the substrate
- The reaction velocity becomes independent of substrate concentration
Question’s Answer: Half of the enzyme molecules are bound to the substrate
A sigmoidal plot of substrate concentration ([S]) versus reaction velocity (V) may indicate.
- Michaelis-Menten kinetics
- Non-competitive inhibition
- Competitive inhibition
- Co-operative binding
Question’s Answer: Co-operative binding
An inducer is not needed in which type of enzyme?
- Allosteric enzyme
- Inducible enzyme
- Constitutive enzyme
- An isoenzyme
Question’s Answer: Constitutive enzyme
The V of an enzyme represents which of the following?
- Substrate concentration
- The amount of active enzyme
- Half the substrate
- The total concentration of the enzymes
Question’s Answer: The amount of active enzyme
Which is characteristic of a competitive inhibitor?
- It may be a feedback inhibitor
- It decreases the Vmax of the enzyme
- It interferes with the binding of the substrate to the active site
- It causes irreversible inhibition
Question’s Answer: It interferes with the binding of the substrate to the active site
Enzymes, which are produced inactive form in the living cells, in are called
- Proenzymes
- Apoenzymes
- Lysozymes
- Ribozymes
Question’s Answer: Proenzymes
Which is a proenzyme?
- angiotensin converting enzyme
- Pepsinogen
- None of these
Question’s Answer: Pepsinogen
The enzyme _______ that adds water across a double bond or removes water to create a double bond without breaking the bonds?
- Hydrolase
- Hydroxylase
- Hydratase
- Esterase
Question’s Answer: Hydratase
Effect of raising the temperature for 20- 80°C on enzyme activity would be.
- Increasing velocity
- Decreasing velocity
- Increasing followed by decreasing velocity
- Both A, B and C
Question’s Answer: Increasing followed by decreasing velocity
Cytochrome P-450 carries which type of enzyme?
- Monoamine oxidase
- Catalase
- Dehydrogenase
- Monooxygenase
Question’s Answer: Monooxygenase
What is the most ideal statement regarding Active Site’ of an enzyme
- Nearly all polypeptide chains must participate in catalysis
- Most of the amino acids involved in Active Site are located near each other on the polypeptide
- Conformation of the Active Site does not exist until the substrate binds
- Amino acids forming Active Site are in close proximity due to specific orientation in space
Question’s Answer: Amino acids forming Active Site are in close proximity due to specific orientation in space
Which of the following is an example of multifunctional enzyme?
- Acetyl-CoA carboxylase
- Pyruvate dehydrogenase complex
- Animal fatty acid synthase
- None of these
Question’s Answer: Animal fatty acid synthase
An enzyme that converts an aldose sugar to a keto-sugar is classified as ______.
- Transferase
- Oxidoreductase
- Isomerase
- Hydrolase
Question’s Answer: Isomerase
If the initial velocity of an enzymatic reaction is equal to Vmax, the substrate concentration is
- Far above KM
- Equal to KM
- Half of K
- Both A, B and C
Question’s Answer: Far above KM
During competitive inhibition, the inhibitor
- Competes with the substrate
- Irreversibly binds with the enzyme
- Competes with the enzyme
- Both A, B and C
Question’s Answer: Competes with the substrate
Competitive inhibitors ______.
- Decrease the VMAX
- Decrease the KM of the enzyme for the substrate
- Increase the VMAX
- Increase the KM of the enzyme for the substrate
Question’s Answer: Increase the KM of the enzyme for the substrate
Which is a therapeutic enzyme?
- Glucose-6-P dehydrogenase
- Streptokinase
- Monoamine oxidase
- Allopurinol
Question’s Answer: Streptokinase
The role of co-enzyme in the enzymatic reactions is
- Enhancing the specificity
- Increasing the number of binding sites on the Apo-enzyme.
- Acting as an acceptor for intermediate products of the substrate
- None of these
Question’s Answer: Acting as an acceptor for intermediate products of the substrate
Which is not true regarding enzymes?
- They remain active even after separation form the source
- They are destroyed after completion of the reaction
- They are destroyed at high temperatures
- Their activity depends upon the pH of the solution
Question’s Answer: They are destroyed after completion of the reaction
Michalis constant (Km) of an enzyme is ______ .
- Dependent upon the enzyme concentration.
- Numerically equal to substrate concentration at VMAX
- Numerically equal VMAX
- Independent of pH
Question’s Answer: Numerically equal to substrate concentration at VMAX
During the estimation of enzyme activity, all of the following are kept constant, excluding
- Enzyme concentration
- pH
- Substrate concentration
- Temperature
Question’s Answer: Enzyme concentration
As per Michalis-Menten equation, at a very low substrate concentration, the initial velocity of the enzymatic reaction is_________.
- Not affected by enzyme concentration
- Nearly equal to Vmax
- Inversely proportional to substrate concentration
- Directly proportional to substrate concentration
Question’s Answer: Directly proportional to substrate concentration
The isoenzymes differ from each other in all of the following, excluding
- Michaelis-Menten constant
- Specific inhibitors
- Amino acid sequence
- Catalytic activity
Question’s Answer: Catalytic activity
What is Lock and Key Theory?
- The active site is flexible and adjusts to the substrate
- The structure of the substrate is identical to the active site
- The Enzyme-Substrate complex has higher energy than free substrate and enzyme
- The active site is complementary to the shape of the substrate
Question’s Answer: The active site is complementary to the shape of the substrate
Which was the first enzyme to be isolated, purified and crystallized?
- Chymotrypsin
- Urease
- Lysozyme
- Ribonuclease
Question’s Answer: Urease
The concept of “Induced Fit as a theory implies which of the following?
- The template theory adequately explains the enzyme mechanism
- The catalytic groups are brought into proper alignment by the substrate
- The conformation of the substrate changes upon binding with the enzyme
- Formation of ES complex is always the fastest step
Question’s Answer: The catalytic groups are brought into proper alignment by the substrate
The alloenzymes are
- Chemically and immunologically different forms of the enzymes
- The same enzyme isolated from different tissues or subcellular compartments
- Structurally related enzyme that carry out different reactions
- Chemically identical enzymes isolated from different species
Question’s Answer: Chemically identical enzymes isolated from different species
Amil Fischer’s Lock-and-key’ theory for enzymes was supported by the fact-
- Size of the active site is very small comared to the total protein
- Co-enzymes act as the ‘key’ at the active site
- Substances similar in structure to that of substrate inhibit enzyme reactions
- The enzyme adapts after binding with the substrate and locks it at the active site
Question’s Answer: Substances similar in structure to that of substrate inhibit enzyme reactions
All _________ enzymes carry Flavin nucleotides as prosthetic group.
- L-Amino acid oxidase
- Xanthine oxidase
- Cytochrome oxidase
- None of these
Question’s Answer: Cytochrome oxidase
Which type of enzyme can supply the citric acid cycle with oxaloacetate from pyruvate?
- A ligase
- A mutase
- An isomerase.
- Both A, B and C
Question’s Answer: A ligase
Cooperativity of an allosteric enzyme can be studied by-
- Michalis-Menten equation
- Hill Equation
- Line weaver-Burk plot
- Both A, B and C
Question’s Answer: Hill Equation
In-vivo of an enzymatic reaction can be controlled by:
- Interconversion b/n forms with different Km values
- Phosphorylation
- Proteolytic.cleavage of the polypeptides
- Both A, B and C
Question’s Answer: Both A, B and C
Which is a co-enzyme?
- Vitamin
- ATP
- Ubiquinone
- Both A, B and C
Question’s Answer: Both A, B and C
Hydrolysis of proteins by protease enzymes would yield amino acids in the form of which of the following?
- Racemic mixture of amino acids
- D-Amino acids
- D. L-Amino acids
- L-Amino acids.
Question’s Answer: L-Amino acids
A number of biochemical assays are linked with enzymatic conversion of NAD NADH. The reaction velocity in these assays is determined by measuring the change in optical density
- 550 nm
- 340 nm
- 290 nm
- 210 nm
Question’s Answer: 340 nm
The Vmax of an enzymatic reaction may be dependent on which of the following?
- K of the enzyme
- Concentration of the enzyme
- Concentration of the competitive inhibitor
- Both A, B and C
Question’s Answer: Concentration of the enzyme
Which is a hydrogen transferring co-enzyme?
- Pyridoxal phosphate
- Thiamine pyrophosphate
- NADP+
- ATP
Question’s Answer: NADP+
According to Steady state kinetics,Which statements is false?
- When [S] =KM, half the substrate binding sites are saturated
- KM is larger than the dissociation constants for [ES]
- Excluding at very low [S], increase in V₁ is less than increase in [S]
- V equals [ES] times k3
Question’s Answer: KM is larger than the dissociation constants for [ES]
Mostly the regulatory reactions in a pathway are enzyme limited, Which is true about such reactions
- They are rate limiting
- They are exergonic and
- They are far from equilibrium irreversible
- Both A, B and C
Question’s Answer: Both A, B and C
The enzymes ______ are always present in a cell/organism at relatively constant concentrations.
- Proenzymes
- Constitutive enzymes
- Functional enzymes
- Facultative enzymes
Question’s Answer: Proenzymes
Which among the following is extracellular?
- Glucose-6-Phosphatase
- Hexokinase
- Pancreatic amylase
- Citrate Synthase
Question’s Answer: Pancreatic amylase
Choose the most ideal statement regarding Allosteric enzymes
- Often found at the first committed step
- Subject to regulation by covalent modification
- They are usually multi-subunit systems
- Both A, B and C
Question’s Answer: Both A, B and C
The isoenzymes are
- Chemically and immunologically different forms of the enzymes
- Chemically and immunologically identical forms of the different enzymes
- Different enzymes that carry out same reactions
- Structurally related enzymes that carry out different reactions
Question’s Answer: Chemically and immunologically different forms of the enzymes
Which enzymes catalyze the binding of two substrates by covalent bonds?
- Lyases
- Ligases
- Synthases
- Reductases
Question’s Answer: Ligases
Who proposed the induced fit model of enzyme action?
- Amil Fischer
- Peter Mitchel
- Daniel Koshland
- Robert Gilbert
Question’s Answer: Daniel Koshland
In lineweaver-Burk plot, the Y-intercept represents
- Vmax
- 1/Vmax
- 1/Km
- Km/Vmax
Question’s Answer: 1/Vmax
Which statements regarding enzyme kinetics is NOT TRUE?
- Value of Km is independent concentration
- Low signifies high affinity for the substrate (s)
- The V is reached when [ES] concentration is maximal
- Enzymes increase the rate of the reaction by enhancing the forward reaction
Question’s Answer: Enzymes increase the rate of the reaction by enhancing the forward reaction
Which is NOT TRUE regarding enzymes
- They lower the activation energy of the reaction
- They change the rate of approach to equilibrium
- They can be very selective with respect to substrate
- They lower the standard free energy of the reaction
Question’s Answer: They lower the standard free energy of the reaction
Which is not a characteristics of allosteric enzymes?
- Feedback inhibition
- Greater specificity than non- allosteric enzymes
- They can be very selective with respect to substrate-
- They lower the standard free energy of the reaction
Question’s Answer: Greater specificity than non-allosteric enzymes
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