Free Enzymes MCQs with Answers
633 Enzymes MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Enzymes are biological catalysts that lower activation energy without being consumed, and their specificity is explained by the lock and key and induced fit models. Work includes the effects of temperature, pH and substrate concentration on reaction rate, plus competitive and non-competitive inhibition and how these differ.
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- A. The active site is rigid
- B. The enzyme changes shape to fit the substrate
- C. The substrate is unchanged
- D. No conformational changes occur
Explanation: Koshland's induced fit model proposes that the enzyme's active site is flexible and changes shape to better accommodate the substrate.
Correct answer: The enzyme changes shape to fit the substrate- A. Bind to allosteric site
- B. Cannot be overcome by increasing substrate
- C. Bind to active site
- D. Change Vmax but not Km
Explanation: Competitive inhibitors bind to the active site, competing with substrate. They can be overcome by increasing substrate concentration.
Correct answer: Bind to active site- A. 2
- B. 7
- C. 8
- D. 10
Explanation: Pepsin works optimally at pH 1.5-2 in the stomach, where it is activated by HCl.
Correct answer: 2- A. Temperature
- B. pH
- C. Substrate concentration
- D. Color of the solution
Explanation: Enzyme activity is affected by temperature, pH, substrate concentration, and presence of inhibitors/activators, but not by color.
Correct answer: Color of the solution- A. Maximum reaction velocity
- B. Substrate concentration at half Vmax
- C. Enzyme concentration
- D. Inhibitor concentration
Explanation: Km is the substrate concentration at which the reaction velocity is half of Vmax. It indicates enzyme-substrate affinity.
Correct answer: Substrate concentration at half Vmax- A. Follow Michaelis-Menten kinetics strictly
- B. Have multiple subunits and regulatory sites
- C. Are not affected by feedback inhibition
- D. Always show competitive inhibition
Explanation: Allosteric enzymes have multiple subunits with regulatory (allosteric) sites where activators or inhibitors bind, affecting enzyme…
Correct answer: Have multiple subunits and regulatory sites- A. RNA polymerase
- B. DNA ligase
- C. Peptidase
- D. Lipase
Explanation: DNA ligase joins Okazaki fragments by forming phosphodiester bonds between adjacent nucleotides.
Correct answer: DNA ligase68. Zymogens are
- A. Active enzymes
- B. Inactive enzyme precursors
- C. Coenzymes
- D. Enzyme inhibitors
Explanation: Zymogens (proenzymes) are inactive precursors that are activated by cleavage, e.g., pepsinogen → pepsin, trypsinogen → trypsin.
Correct answer: Inactive enzyme precursors- A. Stomach
- B. Red blood cells
- C. Pancreas
- D. Liver
Explanation: Carbonic anhydrase in RBCs catalyzes CO2 + H2O ↔ H2CO3, facilitating CO2 transport in blood.
Correct answer: Red blood cells- A. Substrate concentration increases
- B. Enzymes become denatured
- C. Product formation increases
- D. Temperature becomes constant
Explanation: Excess hydrogen or hydroxide ions disturb the ionic and hydrogen bonds between the side chains that hold the tertiary structure, so the…
Correct answer: Enzymes become denatured- A. Carbohydrates
- B. Lipids
- C. Proteins
- D. Nucleic acids
Explanation: Almost every enzyme is a globular protein whose precisely folded tertiary structure creates the active site, which is why heat and extreme…
Correct answer: Proteins- A. Decrease the rate of reaction
- B. Increase the reaction rate until all active sites are saturated
- C. Have no effect on the reaction rate
- D. Increase the rate of reaction in a straight diagonal line
Explanation: Rate rises steeply at first because more collisions occur between substrate and free active sites, then levels off at Vmax once every site…
Correct answer: Increase the reaction rate until all active sites are saturated- A. Rigid and specific
- B. Flexible and specific
- C. Rigid and non specific
- D. Flexible and non specific
Explanation: Fischer's lock and key model treats the active site as a pre formed rigid shape that only the matching substrate fits, which explains…
Correct answer: Rigid and specific- A. Bind permanently and cannot be removed
- B. Bind temporarily and can be removed
- C. Permanently inactivate the enzyme
- D. Change enzyme structure permanently
Explanation: A reversible inhibitor binds through weak interactions and detaches again, so activity returns when it is removed or outcompeted, which is…
Correct answer: Bind temporarily and can be removed- A. lipid
- B. protein
- C. inorganic ion
- D. vitamin
Explanation: Many coenzymes are organic, non-protein helpers derived from vitamins, and they assist enzymes by carrying electrons or chemical groups…
Correct answer: vitamin- A. Jons Jacob Berzelius
- B. Anselme Payen
- C. Walter Bradford Cannon
- D. None of these
Explanation: Anselme Payen and Jean-François Persoz discovered diastase, one of the first recognized enzymes, in 1833.
Correct answer: Anselme Payen- A. only once
- B. only few times
- C. again and again
- D. non of above
Explanation: A coenzyme functions as an organic helper molecule and is usually regenerated or transferred back to its original form during enzyme…
Correct answer: again and again- A. Rate of digestion
- B. Rate of reaction
- C. Level of pH
- D. Number of active sites
Explanation: Enzyme activity is measured by how quickly substrate is converted into product, which is expressed as the rate of reaction.
Correct answer: Rate of reaction- A. Decarboxylase
- B. Hydrolase
- C. Oxidoreductase
- D. Transferase
Explanation: Hydrolases break chemical bonds by adding water, so a dipeptidase hydrolyses the peptide bond and releases two amino acids.
Correct answer: Hydrolase- A. 27?C
- B. 37?C
- C. 47?C
- D. 30?C
Explanation: Most human enzymes have an optimum temperature close to normal body temperature, about 37 °C, where enzyme-substrate collisions and…
Correct answer: 37?C