MCQs on Enzymes

Definition and Classification of Enzymes

1. Which of the following best defines an enzyme?

A. A type of hormone that speeds up reactions
B. A carbohydrate that stores energy
C. A biological catalyst that increases the rate of a reaction
D. A lipid that breaks down proteins

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2. Enzymes are primarily composed of which macromolecule?

A. Nucleic acids
B. Proteins
C. Carbohydrates
D. Lipids

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3. Which of the following is NOT a class of enzymes according to IUBMB classification?

A. Transferases
B. Isomerases
C. Hydrolases
D. Inhibitors

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4. Which enzyme class catalyzes the transfer of functional groups from one molecule to another?

A. Oxidoreductases
B. Transferases
C. Ligases
D. Lyases

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5. Ligases are enzymes that:

A. Break chemical bonds by adding water
B. Transfer electrons between molecules
C. Join two molecules using energy from ATP
D. Rearrange atoms within a molecule

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6. The enzyme class that adds or removes groups to form double bonds is called:

A. Lyases
B. Hydrolases
C. Ligases
D. Transferases

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7. Which enzyme class catalyzes oxidation-reduction reactions?

A. Isomerases
B. Hydrolases
C. Oxidoreductases
D. Lyases

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8. Hydrolases catalyze:

A. Bond formation with ATP
B. Rearrangement of molecular structures
C. Hydrolytic cleavage of bonds using water
D. Removal of electrons

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9. Enzymes are highly specific because of their:

A. High molecular weight
B. Active site configuration
C. pH stability
D. Metal ion content

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10. The IUBMB system classifies enzymes into how many major classes?

A. 4
B. 5
C. 6
D. 8

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✅ Answer Key

1. C

2. B

3. D

4. B

5. C

6. A

7. C

8. C

9. B

10. C

 

Examples of Classification of Enzymes

1. Which of the following enzymes is an example of a hydrolase?

A. Lactate dehydrogenase
B. DNA polymerase
C. Amylase
D. Fumarase

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2. Hexokinase is classified under which class of enzymes?

A. Transferases
B. Isomerases
C. Ligases
D. Lyases

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3. Which of the following enzymes is a ligase?

A. Aldolase
B. DNA ligase
C. Lipase
D. Phosphatase

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4. Which enzyme is an example of an oxidoreductase?

A. Sucrase
B. Urease
C. Alcohol dehydrogenase
D. Isomerase

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5. An example of a lyase is:

A. Pepsin
B. Fumarase
C. DNA ligase
D. Hexokinase

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6. Which of the following enzymes is an isomerase?

A. Phosphoglucomutase
B. Trypsin
C. Urease
D. Pyruvate kinase

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7. Lipase belongs to which class of enzymes?

A. Transferases
B. Oxidoreductases
C. Lyases
D. Hydrolases

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8. Which of these enzymes catalyzes bond formation and belongs to ligases?

A. Catalase
B. DNA ligase
C. Enolase
D. Sucrase

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9. Which of the following is a transferase enzyme?

A. Alanine transaminase (ALT)
B. Peptidase
C. Lactase
D. Isocitrate dehydrogenase

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10. An enzyme that catalyzes the rearrangement within a molecule is called:

A. Lyase
B. Isomerase
C. Transferase
D. Hydrolase

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✅ Answer Key

1. C – Amylase (Hydrolase)

2. A – Hexokinase (Transferase)

3. B – DNA ligase (Ligase)

4. C – Alcohol dehydrogenase (Oxidoreductase)

5. B – Fumarase (Lyase)

6. A – Phosphoglucomutase (Isomerase)

7. D – Lipase (Hydrolase)

8. B – DNA ligase (Ligase)

9. A – Alanine transaminase (Transferase)

10. B – Isomerase

 

Holoenzyme, Apoenzyme, Coenzyme, Cofactor, Prosthetic Group, Proenzyme

1. What is a holoenzyme?

A. The non-protein part of an enzyme
B. The protein part of an enzyme only
C. The active enzyme consisting of apoenzyme and cofactor
D. An enzyme that is irreversibly inhibited

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2. Which of the following best defines an apoenzyme?

A. A complete enzyme with its cofactor
B. The protein part of the enzyme without its coenzyme
C. A metallic ion that activates enzymes
D. A non-protein organic molecule

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3. Coenzymes are:

A. Always metal ions
B. Protein components of enzymes
C. Organic non-protein molecules required for enzyme activity
D. Inhibitors of enzymes

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4. A cofactor is:

A. Always a protein
B. The inactive form of an enzyme
C. A non-protein component essential for enzyme activity
D. A denatured enzyme

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5. Which of the following is an example of a coenzyme?

A. Fe²⁺
B. NAD⁺
C. Zn²⁺
D. Mg²⁺

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6. A prosthetic group is defined as:

A. A loosely bound coenzyme
B. A permanently attached non-protein component
C. A part of the active site of all enzymes
D. A type of inhibitor

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7. Which statement is TRUE about apoenzymes?

A. They are active on their own
B. They are non-protein cofactors
C. They require cofactors/coenzymes to become active
D. They are coenzymes

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8. The inactive part of an enzyme is called:

A. Proenzyme
B. Coenzyme
C. Apoenzyme
D. Holoenzyme

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9. Which of the following is a metallic cofactor?

A. FAD
B. NADP⁺
C. Zn²⁺
D. Biotin

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10. Example of proenzyme

A. Trypsin
B. Pepsin
C. Plasmin
D. Trypsinogen

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✅ Answer Key

1. C – The active enzyme consisting of apoenzyme and cofactor

2. B – The protein part of the enzyme without its coenzyme

3. C – Organic non-protein molecules required for enzyme activity

4. C – A non-protein component essential for enzyme activity

5. B – NAD⁺

6. B – A permanently attached non-protein component

7. C – They require cofactors/coenzymes to become active

8. A – Proenzyme

9. C – Zn²⁺

10. D – Trypsinogen

 

Mechanism of Enzyme Action & Theories of Enzyme-Substrate Complex Formation

1. The first step in enzyme action involves:

A. Product release from enzyme
B. Covalent modification of the enzyme
C. Formation of enzyme-substrate complex
D. Denaturation of enzyme

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2. Which theory suggests that the enzyme’s active site has a rigid structure complementary to the substrate?

A. Induced fit theory
B. Lock and key theory
C. Collision theory
D. Transition state theory

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3. The “induced fit” model of enzyme action was proposed by:

A. Emil Fischer
B. Linus Pauling
C. Daniel Koshland
D. Michaelis and Menten

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4. According to the lock and key theory, enzyme specificity is due to:

A. Change in enzyme shape after substrate binds
B. The presence of cofactors
C. Pre-existing complementary shape of enzyme and substrate
D. Substrate phosphorylation

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5. In the induced fit theory, the enzyme:

A. Acts only after denaturation
B. Undergoes a conformational change upon substrate binding
C. Is consumed in the reaction
D. Binds irreversibly with the substrate

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6. Which of the following best describes the transition state in enzyme catalysis?

A. Stable enzyme-substrate complex
B. Final product of reaction
C. High-energy intermediate between substrate and product
D. Inactive enzyme form

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7. What is the role of the active site in an enzyme?

A. To bind water molecules
B. To lower the temperature of the reaction
C. To bind the substrate and catalyze the reaction
D. To act as a structural protein

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8. Which of the following represents the correct sequence of enzyme action?

A. Product → Enzyme-substrate complex → Substrate
B. Enzyme-substrate complex → Substrate → Product
C. Substrate → Enzyme-substrate complex → Product
D. Substrate → Product → Enzyme-substrate complex

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9. Enzymes increase the rate of reactions by:

A. Increasing temperature
B. Increasing activation energy
C. Decreasing activation energy
D. Altering the reaction equilibrium

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10. The binding of a substrate to an enzyme is usually through:

A. Covalent bonds only
B. Irreversible bonds
C. Non-covalent interactions such as hydrogen bonds and van der Waals forces
D. Strong ionic bonds only

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✅ Answer Key

1. C – Formation of enzyme-substrate complex

2. B – Lock and key theory

3. C – Daniel Koshland

4. C – Pre-existing complementary shape of enzyme and substrate

5. B – Undergoes a conformational change upon substrate binding

6. C – High-energy intermediate between substrate and product

7. C – To bind the substrate and catalyze the reaction

8. C – Substrate → Enzyme-substrate complex → Product

9. C – Decreasing activation energy

10. C – Non-covalent interactions such as hydrogen bonds and van der Waals forces

 

Factors Affecting Enzyme Activity

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1. Which of the following factors does NOT affect enzyme activity?

A. Temperature
B. pH
C. Substrate concentration
D. Light intensity

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2. Enzymes typically show maximum activity at:

A. Low temperature and low pH
B. High temperature and low pH
C. Optimum temperature and optimum pH
D. Room temperature only

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3. What happens to most enzymes at very high temperatures?

A. Increased activity
B. Denaturation
C. Freezing
D. Stabilization

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4. The pH at which an enzyme shows maximum activity is called:

A. Neutral pH
B. Peak pH
C. Acidic pH
D. Optimum pH

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5. As substrate concentration increases, the enzyme activity:

A. Decreases continuously
B. Increases and then levels off
C. Stays the same
D. Stops immediately

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6. Enzyme activity is measured in terms of:

A. Enzyme concentration
B. Rate of product formation
C. Number of cofactors
D. pH change only

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7. Effect of temperature on enzyme activity, graph looks like

A. Linear
B. Sigmoidal
C. Bell shaped
D. Rectangular hyperbola

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8. Optimum pH for most of human enzymes

A. 1-3
B. 3-5
C. 6-8
D. 8-10

9. At enzyme saturation, increasing substrate concentration will:

A. Decrease enzyme activity
B. Increase enzyme activity linearly
C. Have no effect on enzyme activity
D. Stop the enzyme reaction

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10. Effect of substrate concentration on enzyme activity, graph looks like

A. Linear
B. Sigmoidal
C. Bell shaped
D. Rectangular hyperbola

 

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✅ Answer Key

1. D – Light intensity

2. C – Optimum temperature and optimum pH

3. B – Denaturation

4. D – Optimum pH

5. B – Increases and then levels off

6. B – Rate of product formation

7. C – Bell shaped

8. C – 6-8

9. C – Have no effect on enzyme activity

10. D – Rectangular hyperbola

 

Km Value and Vmax

1. Km is defined as the substrate concentration at which the reaction rate is:

A. Zero
B. Equal to Vmax
C. Half of Vmax
D. Double the enzyme concentration

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2. Vmax represents:

A. Maximum product formed per mole of substrate
B. Maximum velocity when enzyme is fully saturated with substrate
C. Minimum rate of reaction
D. Enzyme concentration in the reaction

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3. A low Km value indicates:

A. Low affinity between enzyme and substrate
B. High affinity between enzyme and substrate
C. No reaction
D. Enzyme inhibition

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4. When substrate concentration is much higher than Km, the rate of reaction approaches:

A. Zero
B. Half of Vmax
C. Vmax
D. Infinity

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5. Which of the following statements is TRUE regarding Vmax?

A. It decreases as enzyme concentration increases
B. It is reached when all enzyme active sites are occupied
C. It is independent of enzyme concentration
D. It is the initial velocity at zero substrate

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6. Km is a measure of:

A. The energy required for activation
B. The number of enzyme molecules
C. The affinity of enzyme for its substrate
D. The product concentration

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7. In Michaelis-Menten kinetics, if Km is much greater than the substrate concentration, the rate of reaction is:

A. Near Vmax
B. Proportional to enzyme concentration only
C. Very low and dependent on substrate concentration
D. Independent of substrate concentration

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8. Vmax can be increased by:

A. Increasing substrate concentration
B. Increasing enzyme concentration
C. Decreasing pH
D. Adding competitive inhibitor

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9. The unit of Km is typically:

A. mg/ml
B. mol
C. μmol/min
D. Same as substrate concentration (e.g., mM)

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10. The Michaelis-Menten equation relates reaction rate to:

A. Temperature and pH
B. Substrate concentration and enzyme size
C. Substrate concentration and enzyme-substrate affinity
D. Product concentration and enzyme activity

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✅ Answer Key

1. C – Half of Vmax

2. B – Maximum velocity when enzyme is fully saturated with substrate

3. B – High affinity between enzyme and substrate

4. C – Vmax

5. B – It is reached when all enzyme active sites are occupied

6. C – The affinity of enzyme for its substrate

7. C – Very low and dependent on substrate concentration

8. B – Increasing enzyme concentration

9. D – Same as substrate concentration (e.g., mM)

10. C – Substrate concentration and enzyme-substrate affinity

 

Enzyme Inhibition and Its Significance

1. Enzyme inhibition refers to:

A. Activation of enzyme by substrate
B. Increase in enzyme activity
C. Decrease or loss of enzyme activity due to a substance
D. Enzyme binding to coenzymes

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2. Competitive inhibition occurs when the inhibitor:

A. Binds to a site other than the active site
B. Is a product of the reaction
C. Competes with the substrate for the active site
D. Enhances enzyme activity

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3. In non-competitive inhibition, the inhibitor binds to:

A. The substrate
B. The active site
C. The enzyme-substrate complex only
D. A site other than the active site

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4.  Feedback inhibition is an example of type of  inhibition?

A. Competitive
B. Non-competitive
C. Allosteric
D. Suicide inhibition

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5. Competitive inhibition can be reversed by:

A. Increasing enzyme concentration
B. Decreasing product concentration
C. Increasing substrate concentration
D. Heating the reaction mixture

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6. In non-competitive inhibition, Vmax is:

A. Increased
B. Decreased
C. Unchanged
D. Doubled

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7. Which of the following is an example of irreversible enzyme inhibition?

A. Penicillin action on bacterial transpeptidase
B. Malonate inhibiting succinate dehydrogenase
C. ATP inhibiting phosphofructokinase
D. Statin inhibition of HMG-CoA reductase

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8. Significance of enzyme inhibition in medicine includes:

A. Enhancing enzyme synthesis
B. Blocking metabolic pathways in pathogens
C. Decreasing drug half-life
D. Preventing enzyme denaturation

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9. Allosteric inhibition involves:

A. Competitive binding at active site
B. Binding at a site other than the active site, altering enzyme shape
C. Breakdown of the enzyme
D. Irreversible covalent modification

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10. In competitive inhibition, Km:

A. Increases
B. Decreases
C. Remains unchanged
D. Becomes zero

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✅ Answer Key

1. C – Decrease or loss of enzyme activity due to a substance

2. C – Competes with the substrate for the active site

3. D – A site other than the active site

4. C – Allosteric inhibition

5. C – Increasing substrate concentration

6. B – Decreased

7. A – Penicillin action on bacterial transpeptidase

8. B – Blocking metabolic pathways in pathogens

9. B – Binding at a site other than the active site, altering enzyme shape

10. A – Increases

 

Clinical Significance of Enzymes

1. Which of the following enzymes is most commonly used to diagnose myocardial infarction (MI)?

A. Alkaline phosphatase (ALP)
B. Amylase
C. Creatine kinase-MB (CK-MB)
D. Aspartate transaminase (AST)

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2. Elevated levels of alkaline phosphatase (ALP) are commonly associated with:

A. Myocardial infarction
B. Pancreatitis
C. Liver and bone disorders
D. Renal failure

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3. Which enzyme is used as a marker for acute pancreatitis?

A. AST
B. CK-MB
C. Amylase
D. LDH

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4. Alanine transaminase (ALT) is a specific marker for:

A. Kidney function
B. Brain disorders
C. Liver cell injury
D. Bone diseases

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5. An increase in serum lactate dehydrogenase (LDH) can be seen in:

A. Hypothyroidism
B. Myocardial infarction and liver diseases
C. Hypercalcemia
D. Diabetes mellitus

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6. Which isoenzyme of creatine kinase is specific for cardiac muscle?

A. CK-MM
B. CK-BB
C. CK-MB
D. CK-LD

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7. Prostate-specific antigen (PSA) is:

A. An enzyme found in urine
B. A hormone regulating male fertility
C. A marker enzyme used in prostate cancer diagnosis
D. A liver enzyme

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8. Increased levels of gamma-glutamyl transferase (GGT) suggest:

A. Myocardial infarction
B. Chronic alcohol consumption or liver damage
C. Bone metastasis
D. Acute kidney failure

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9. Marker enzyme for obstructive jaundice is

A. Acid phosphatase
B. Amylase
C. LDH
D. ALP

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10. Enzymes are used in clinical diagnosis because:

A. They are not affected by diseases
B. Their levels remain constant
C. Their levels change in specific diseases
D. They are always elevated in all conditions

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✅ Answer Key

1. C – Creatine kinase-MB (CK-MB)

2. C – Liver and bone disorders

3. C – Amylase

4. C – Liver cell injury

5. B – Myocardial infarction and liver diseases

6. C – CK-MB

7. C – A marker enzyme used in prostate cancer diagnosis

8. B – Chronic alcohol consumption or liver damage

9. D – ALP

10. C – Their levels change in specific diseases

 

Isoenzymes and Their Clinical Significance

1. Isoenzymes are:

A. Enzymes with different functions but similar structure
B. Enzymes with identical amino acid sequences
C. Different molecular forms of the same enzyme catalyzing the same reaction
D. Inactive forms of enzymes

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2. Which of the following enzymes exists in multiple isoenzymic forms?

A. Amylase
B. Creatine kinase (CK)
C. Urease
D. Sucrase

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3. Isoenzymes of Alkaline phosphatase (ALP) are originated from all, EXCEPT

A. Liver
B. Placenta
C. Bone
D. Heart

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4. In myocardial infarction (MI), which LDH isoenzyme is elevated first?

A. LDH-5
B. LDH-4
C. LDH-2
D. LDH-1

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5. The isoenzyme CK-MB is primarily associated with which tissue?

A. Skeletal muscle
B. Brain
C. Cardiac muscle
D. Liver

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6. LDH isoenzymes can be separated by:

A. Chromatography
B. Spectrophotometry
C. Electrophoresis
D. Colorimetry

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7. Which isoenzyme of CK is found mainly in the brain?

A. CK-MM
B. CK-MB
C. CK-BB
D. CK-LD

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8. Clinical significance of isoenzymes lies in:

A. Identifying enzyme cofactors
B. Differentiating tissue-specific damage
C. Calculating enzyme molecular weight
D. Measuring DNA synthesis

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9. An LDH “flipped pattern” (LDH-1 > LDH-2) is characteristic of:

A. Liver cirrhosis
B. Pancreatitis
C. Myocardial infarction
D. Bone disease

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10. CK-MM isoenzyme is most abundant in:

A. Cardiac muscle
B. Smooth muscle
C. Brain tissue
D. Skeletal muscle

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✅ Answer Key

1. C – Different molecular forms of the same enzyme catalyzing the same reaction

2. B – Creatine kinase (CK)

3. D – Heart

4. D – LDH-1

5. C – Cardiac muscle

6. C – Electrophoresis

7. C – CK-BB

8. B – Differentiating tissue-specific damage

9. C – Myocardial infarction

10. D – Skeletal muscle

 

Case-Based Questions on Clinical Significance of Enzymes and Isoenzymes

Question 1:

A 55-year-old male presents with chest pain radiating to the left arm. ECG shows ST-segment elevation.

Which is the first enzyme to rise and helps in  diagnosing myocardial infarction in this patient?

A. Lactate dehydrogenase (LDH)

B. Creatine kinase-MB (CK-MB)

C. Aspartate transaminase (AST)

D. Troponin I

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Question 2:

A 45-year-old chronic alcoholic presents with abdominal pain radiating to the back. Serum amylase and lipase are elevated.

Which enzyme is more specific for diagnosing acute pancreatitis?

A. Amylase

B. Lipase

C. ALT

D. ALP

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Question 3:

A 5-year-old child is brought with muscle weakness and delayed milestones. CPK-MM levels are elevated.

Which disease is most likely in this child?

A. Myocardial infarction

B. Acute pancreatitis

C. Muscular dystrophy

D. Viral hepatitis

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Question 4:

A patient with liver cirrhosis shows a marked increase in gamma-glutamyl transferase (GGT) and ALP levels.

What is the significance of elevated GGT in this context?

A. Indicates cardiac damage

B. Suggests alcohol-induced liver damage

C. Confirms pancreatitis

D. Rules out liver disease

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Question 5:

A patient suspected of myocardial infarction has elevated LDH1 over LDH2.

This pattern is referred to as:

A. Isoenzyme reversal (Flipped Pattern)

B. Enzyme inactivation

C. Zymogen activation

D. Protein denaturation

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Question 6:

A 30-year-old man presents with jaundice. Lab results show increased ALT and AST, with ALT > AST.

What is the most likely cause?

A. Alcoholic liver disease

B. Viral hepatitis

C. Hemolytic anemia

D. Myocardial infarction

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Question 7:

In a suspected case of prostate cancer, which of the following enzyme markers would most likely be elevated?

A. CK-MB

B. ALP (Bone isoenzyme)

C. Acid phosphatase

D. AST

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Question 8:

A patient with bone metastasis shows a marked increase in alkaline phosphatase.

Which isoenzyme is elevated in this condition?

A. Liver ALP

B. Intestinal ALP

C. Placental ALP

D. Bone ALP

Question 9:

A 60-year-old male presents with fatigue, weight loss, and bone pain. Laboratory investigations reveal high serum ALP and normal GGT.

Which of the following is the most likely diagnosis?

A. Alcoholic liver disease
B. Cholestatic jaundice
C. Paget’s disease of bone
D. Viral hepatitis

Question 10:

A patient was suspected of myocardial infarction.

Which of the following enzyme is NOT a cardiac Marker?

A. AST
B. LDH
C. CPK
D. ALT

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✅ Answer Key:

1. B. Creatine kinase-MB (CK-MB)

2. B. Lipase

3. C. Muscular dystrophy

4. B. Suggests alcohol-induced liver damage

5. A. Isoenzyme reversal (Flipped Pattern)

6. B. Viral hepatitis

7. C. Acid phosphatase

8. D. Bone ALP

9. C. Paget’s disease of bone
10. D. ALT

 

Revision Questions

1. Which of the following is an example of a lyase enzyme?
   A. Acetyl‑CoA carboxylase
   B. Aldolase
   C. Fatty acyl CoA dehydrogenase
   D. Glutathione reductase

2. Which statement is false about oxygenases?
   A. Monooxygenases incorporate one atom of molecular oxygen into substrate.
   B. Dioxygenases incorporate both atoms of O₂ into substrate.
   C. They catalyse carboxylation reactions of all drugs.
   D. Important in hydroxylation of steroids.

3. All of the following are oxidoreductases except:
   A. Dehydrogenases
   B. Peroxidases
   C. Hydrolases
   D. Oxygenases

4. Which type of enzyme inhibition increases the Km but leaves Vmax unchanged?
   A. Noncompetitive inhibition
   B. Uncompetitive inhibition
   C. Competitive inhibition
   D. Mixed inhibition

5. Uncompetitive inhibition is characterized by which of the following changes?
   A. ↑ Km, no change Vmax
   B. ↓ Km, ↓ Vmax
   C. No change Km, ↓ Vmax
   D. ↑ both Km & Vmax

6. Chymotrypsin cleaves at which kind of amino acids’ peptide bond (on the carboxyl side)?
   A. Basic amino acids (Arg, Lys)
   B. Acidic amino acids (Asp, Glu)
   C. Large hydrophobic amino acids (Phe, Trp, Tyr)
   D. Small neutral amino acids (Gly, Ala)

7. Which of the following is true about zymogens?
   A. They are irreversible inhibitors of enzymes.
   B. They are active forms of proteolytic enzymes.
   C. They require proteolytic cleavage to become active.
   D. They are always secreted in their active form.

8. Which coenzyme is required by decarboxylation reactions (e.g. pyruvate dehydrogenase)?
   A. Riboflavin (FAD)
   B. Biotin
   C. Thiamine pyrophosphate (TPP)
   D. Pyridoxal phosphate (PLP)

9. Biotin is a coenzyme for which kind of reactions?
   A. Transamination
   B. Carboxylation
   C. Oxidation‑reduction
   D. Decarboxylation

10. The catalytically active part of an enzyme (excluding any cofactor or coenzyme) is termed:
    A. Holoenzyme
    B. Apoenzyme
    C. Cofactor
    D. Coenzyme

11. Which of the following covalent modifications can regulate enzyme activity?
    A. Phosphorylation
    B. Acetylation
    C. ADP‑ribosylation
    D. All of the above

12. Which parameter(s) of enzyme kinetics is/are reduced by a noncompetitive inhibitor?
    A. Km increased, Vmax same
    B. Km same, Vmax decreased
    C. Both Km & Vmax decreased
    D. Vmax increased, Km same

13. Isoenzymes are characterized by:
    A. Catalysing different reactions
    B. Having same amino acid sequence
    C. Having different distribution in tissues
    D. Being coded by same gene always

14. Regarding the model of enzyme‐substrate interaction, which model suggests that the active site is rigid and exactly complementary to the substrate?
    A. Induced fit model
    B. Lock and key model
    C. Transition‑state model
    D. Conformational selection model

15. Which of the following enzymes is not correctly matched with its marker location?
    A. Alkaline phosphatase — biliary tract /apical membrane
    B. Glucose‑6‑phosphatase — endoplasmic reticulum of hepatocytes
    C. 5’‑Nucleotidase — plasma membrane marker
    D. Catalase — mitochondrial matrix

16. Malonate acts as an inhibitor of succinate dehydrogenase. What type of inhibition is this?
    A. Competitive
    B. Noncompetitive
    C. Uncompetitive
    D. Irreversible

17. What happens to enzyme kinetics in competitive inhibition if substrate concentration is increased to very high?
    A. Vmax decreases
    B. Km decreases
    C. Vmax same, Km increases
    D. Km eventually becomes similar to the original (in effect)

18. Which of the following statements about competitive inhibition is true?
    A. Increases Vmax, Km stays the same
    B. Decreases Vmax, Km stays the same
    C. Km increases, Vmax remains unchanged
    D. Both Km and Vmax decrease

19. Which coenzyme is derived from niacin?
    A. CoA
    B. FMN
    C. NAD⁺ / NADP⁺
    D. TPP

20. Which enzyme in the following is a mixed function oxidase / monooxygenase?
    A. Xanthine oxidase
    B. Cytochrome P450
    C. Aldolase
    D. Lipase

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✅ Answer Key