Pharmacy MCQ

MCQ on Enzymes and Metabolic Pathways

By Biology Ease 6 min read

🟢 EASY (1–20)

  1. What are enzymes?
    a) Carbohydrates
    b) Proteins ✅
    c) Lipids
    d) Vitamins
    Explanation: Most enzymes are proteins that catalyze biochemical reactions.
  2. Which of the following is a characteristic of enzymes?
    a) Consumed in reactions
    b) Slow down reactions
    c) Catalyze reactions ✅
    d) Form part of DNA
    Explanation: Enzymes speed up reactions without being consumed.
  3. The substance upon which an enzyme acts is called:
    a) Product
    b) Catalyst
    c) Substrate ✅
    d) Coenzyme
    Explanation: Substrate is the molecule that binds to the enzyme’s active site.
  4. Enzymes work best at specific:
    a) Colors
    b) Temperatures and pH ✅
    c) Volumes
    d) Pressures
    Explanation: Each enzyme has an optimal temperature and pH for activity.
  5. Which enzyme breaks down starch?
    a) Lipase
    b) Protease
    c) Amylase ✅
    d) Sucrase
    Explanation: Amylase hydrolyzes starch into simpler sugars.
  6. Lipase helps in the digestion of:
    a) Carbohydrates
    b) Fats ✅
    c) Proteins
    d) Minerals
    Explanation: Lipase breaks down lipids (fats) into fatty acids and glycerol.
  7. Which of the following is a coenzyme?
    a) Mg²⁺
    b) Vitamin B6 ✅
    c) Water
    d) Oxygen
    Explanation: Many vitamins, like B6, act as coenzymes.
  8. What type of biomolecule are most enzymes?
    a) Lipids
    b) Proteins ✅
    c) Sugars
    d) DNA
    Explanation: Most enzymes are proteinaceous in nature.
  9. Which enzyme is present in saliva?
    a) Pepsin
    b) Trypsin
    c) Amylase ✅
    d) Urease
    Explanation: Salivary amylase initiates carbohydrate digestion.
  10. The energy barrier that enzymes help lower is called:
    a) Activation energy ✅
    b) Enthalpy
    c) Entropy
    d) Catalysis energy
    Explanation: Enzymes lower the activation energy needed for a reaction.
  11. Which enzyme breaks down proteins in the stomach?
    a) Amylase
    b) Lipase
    c) Pepsin ✅
    d) Lactase
    Explanation: Pepsin breaks proteins into peptides in acidic environments.
  12. What is the function of ATP in metabolic pathways?
    a) Enzyme
    b) Inhibitor
    c) Energy carrier ✅
    d) Vitamin
    Explanation: ATP stores and transfers energy for cellular processes.
  13. In glycolysis, glucose is converted into:
    a) Pyruvate ✅
    b) Acetyl-CoA
    c) ATP
    d) Fructose
    Explanation: Glycolysis breaks down glucose to produce pyruvate.
  14. Which of the following enzymes catalyzes ATP synthesis?
    a) Kinase
    b) ATP synthase ✅
    c) Protease
    d) Amylase
    Explanation: ATP synthase generates ATP in oxidative phosphorylation.
  15. Which of the following inhibits enzyme activity?
    a) Coenzyme
    b) Activator
    c) Inhibitor ✅
    d) Catalyst
    Explanation: Inhibitors decrease or block enzyme activity.
  16. The active site of an enzyme is:
    a) Where it binds to other enzymes
    b) Where substrate binds ✅
    c) Where DNA is made
    d) Unrelated to function
    Explanation: The active site is the region where substrate binds and reacts.
  17. Which enzyme breaks down hydrogen peroxide?
    a) Catalase ✅
    b) Peroxidase
    c) Amylase
    d) Lipase
    Explanation: Catalase breaks H₂O₂ into water and oxygen.
  18. Which coenzyme is derived from vitamin B3 (niacin)?
    a) NAD+ ✅
    b) FAD
    c) TPP
    d) CoA
    Explanation: NAD+ is derived from niacin and is involved in redox reactions.
  19. Which process occurs in the mitochondria?
    a) Glycolysis
    b) Electron transport chain ✅
    c) Fermentation
    d) Photosynthesis
    Explanation: The electron transport chain takes place in mitochondria.
  20. Which metabolic pathway produces the most ATP?
    a) Glycolysis
    b) Fermentation
    c) Citric acid cycle
    d) Electron transport chain ✅
    Explanation: The electron transport chain is the major ATP-producing process.

🟡 MODERATE (21–40)

  1. The enzyme that converts pyruvate to acetyl-CoA is:
    a) Pyruvate kinase
    b) Pyruvate dehydrogenase ✅
    c) Hexokinase
    d) Enolase
    Explanation: Pyruvate dehydrogenase links glycolysis and the Krebs cycle.
  2. Enzymes that transfer phosphate groups are called:
    a) Isomerases
    b) Kinases ✅
    c) Oxidases
    d) Ligases
    Explanation: Kinases catalyze phosphorylation.
  3. Which pathway is anaerobic?
    a) Krebs cycle
    b) Electron transport chain
    c) Glycolysis ✅
    d) Oxidative phosphorylation
    Explanation: Glycolysis does not require oxygen.
  4. Enzyme inhibition that is reversible and competes for active site:
    a) Allosteric
    b) Competitive ✅
    c) Non-competitive
    d) Irreversible
    Explanation: Competitive inhibitors resemble the substrate and bind at the active site.
  5. Which vitamin is a precursor of FAD?
    a) Vitamin C
    b) Vitamin B2 (Riboflavin) ✅
    c) Vitamin A
    d) Vitamin D
    Explanation: Riboflavin is the precursor of FAD.
  6. Which enzyme regulates glycolysis?
    a) Enolase
    b) Hexokinase
    c) Phosphofructokinase-1 (PFK-1) ✅
    d) Pyruvate kinase
    Explanation: PFK-1 is a key regulatory enzyme in glycolysis.
  7. What type of reaction does oxidase catalyze?
    a) Hydrolysis
    b) Oxidation ✅
    c) Reduction
    d) Isomerization
    Explanation: Oxidases catalyze electron transfer to oxygen.
  8. The Krebs cycle takes place in the:
    a) Cytoplasm
    b) Mitochondrial matrix ✅
    c) Nucleus
    d) Chloroplast
    Explanation: The matrix is the site of the citric acid cycle.
  9. Which enzyme synthesizes DNA from RNA?
    a) RNA polymerase
    b) Reverse transcriptase ✅
    c) DNA ligase
    d) DNA polymerase
    Explanation: Reverse transcriptase creates DNA from an RNA template.
  10. In gluconeogenesis, which molecule is synthesized?
    a) Lipids
    b) Glucose ✅
    c) Urea
    d) ATP
    Explanation: Gluconeogenesis produces glucose from non-carbohydrate sources.
  11. Which of the following enzymes is used in PCR?
    a) Taq polymerase ✅
    b) Ligase
    c) Helicase
    d) Endonuclease
    Explanation: Taq polymerase is heat-stable and used in DNA amplification.
  12. Which enzyme catalyzes the first step of glycolysis?
    a) Enolase
    b) Hexokinase ✅
    c) Pyruvate kinase
    d) Aldolase
    Explanation: Hexokinase phosphorylates glucose to glucose-6-phosphate.
  13. What is the end product of anaerobic glycolysis in humans?
    a) Ethanol
    b) Pyruvate
    c) Lactate ✅
    d) Acetyl-CoA
    Explanation: In the absence of oxygen, pyruvate is converted to lactate.
  14. An allosteric site on an enzyme is:
    a) Always inactive
    b) Same as active site
    c) Site for non-substrate binding ✅
    d) DNA-binding site
    Explanation: Allosteric sites bind regulators, affecting enzyme activity.
  15. An example of a metabolic pathway is:
    a) Osmosis
    b) Digestion
    c) Glycolysis ✅
    d) Filtration
    Explanation: Glycolysis is a well-defined metabolic pathway.
  16. A zymogen is an enzyme that is:
    a) Overactive
    b) Inactive precursor ✅
    c) Hormone
    d) Nucleic acid
    Explanation: Zymogens are inactive enzymes that require activation.
  17. Which process converts ADP to ATP?
    a) Hydrolysis
    b) Phosphorylation ✅
    c) Oxidation
    d) Reduction
    Explanation: Addition of a phosphate group generates ATP.
  18. Which enzyme removes CO₂ from a compound?
    a) Dehydrogenase
    b) Decarboxylase ✅
    c) Ligase
    d) Kinase
    Explanation: Decarboxylases catalyze the removal of carbon dioxide.
  19. Inhibitors that bind to sites other than the active site are called:
    a) Competitive
    b) Non-competitive ✅
    c) Substrate analogs
    d) Cofactors
    Explanation: These inhibitors bind elsewhere and change enzyme shape.
  20. The final electron acceptor in aerobic respiration is:
    a) NAD+
    b) FAD
    c) Oxygen ✅
    d) Carbon dioxide
    Explanation: Oxygen accepts electrons and forms water.

🔴 HARD (41–50)

  1. Which pathway is shared between aerobic and anaerobic respiration?
    a) Krebs cycle
    b) Electron transport chain
    c) Glycolysis ✅
    d) Oxidative phosphorylation
    Explanation: Glycolysis occurs in both conditions.
  2. Enzymes that catalyze bond formation with energy input are called:
    a) Isomerases
    b) Ligases ✅
    c) Transferases
    d) Lyases
    Explanation: Ligases join molecules using ATP.
  3. Which metabolic pathway is catabolic?
    a) Gluconeogenesis
    b) Glycogenesis
    c) Glycolysis ✅
    d) Lipogenesis
    Explanation: Glycolysis breaks down glucose to release energy.
  4. Which enzyme catalyzes the final step of glycolysis?
    a) Aldolase
    b) Pyruvate kinase ✅
    c) Hexokinase
    d) Enolase
    Explanation: Pyruvate kinase converts phosphoenolpyruvate to pyruvate.
  5. Which of the following is a product of the urea cycle?
    a) ATP
    b) Urea ✅
    c) Ammonia
    d) Pyruvate
    Explanation: The urea cycle eliminates nitrogen as urea.
  6. Apoenzyme becomes active when bound to a:
    a) Cofactor ✅
    b) Substrate
    c) Product
    d) Zymogen
    Explanation: Apoenzyme + cofactor = holoenzyme.
  7. Which enzyme deficiency causes phenylketonuria (PKU)?
    a) Amylase
    b) Tyrosinase
    c) Phenylalanine hydroxylase ✅
    d) Lactase
    Explanation: Deficiency leads to accumulation of phenylalanine.
  8. The term “holoenzyme” refers to:
    a) Inactive enzyme
    b) Substrate
    c) Apoenzyme + cofactor ✅
    d) Competitive inhibitor
    Explanation: Holoenzyme is the active form.
  9. In the ETC, electrons move through complexes to:
    a) Pump water
    b) Generate light
    c) Create a proton gradient ✅
    d) Make glucose
    Explanation: The gradient drives ATP synthesis.
  10. Which is not a part of the citric acid cycle?
    a) Fumarate
    b) Citrate
    c) Oxaloacetate
    d) Glucose ✅
    Explanation: Glucose enters glycolysis, not the Krebs cycle directly.