1. Enzymes are classified as which type of biological molecule?
a) Lipids
b) Proteins
c) Carbohydrates
d) Nucleic acids
Answer: b) Proteins
Explanation: Most enzymes are proteins, though some RNA molecules (ribozymes) can also act as enzymes. They are made of amino acids and folded into specific shapes to perform catalytic functions.

2. What is the term for enzymes that work outside the cell that produces them?
a) Intracellular enzymes
b) Extracellular enzymes
c) Endoenzymes
d) Apoenzymes
Answer: b) Extracellular enzymes
Explanation: Extracellular enzymes, like digestive enzymes, are secreted out of the cell and function externally to break down macromolecules.

3. Which metal ion is a cofactor for the enzyme carbonic anhydrase?
a) Zinc (Zn²⁺)
b) Iron (Fe²⁺)
c) Magnesium (Mg²⁺)
d) Calcium (Ca²⁺)
Answer: a) Zinc (Zn²⁺)
Explanation: Zinc acts as a cofactor for carbonic anhydrase, enabling the enzyme to catalyze the conversion of carbon dioxide and water into bicarbonate and protons.

4. How does temperature affect enzyme activity?
a) Increases activity at all temperatures
b) Decreases activity at high temperatures only
c) Optimum activity at specific temperatures, then declines
d) Temperature has no effect
Answer: c) Optimum activity at specific temperatures, then declines
Explanation: Enzymes have an optimal temperature at which they function best. High temperatures can denature them, while low temperatures slow their activity.

5. What is an allosteric site on an enzyme?
a) The active site where substrates bind
b) A site where inhibitors or activators bind
c) The part of the enzyme that catalyzes the reaction
d) A region that denatures under high temperatures
Answer: b) A site where inhibitors or activators bind
Explanation: The allosteric site is separate from the active site and allows molecules to regulate enzyme activity by changing its shape.

6. Which type of enzyme inhibitor binds irreversibly to the active site?
a) Competitive inhibitor
b) Non-competitive inhibitor
c) Uncompetitive inhibitor
d) Suicide inhibitor
Answer: d) Suicide inhibitor
Explanation: Suicide inhibitors irreversibly bind to the enzyme’s active site, rendering the enzyme permanently inactive.

7. What is the primary difference between cofactors and coenzymes?
a) Cofactors are organic, coenzymes are inorganic
b) Cofactors are inorganic, coenzymes are organic
c) Both are the same
d) Only coenzymes bind to the active site
Answer: b) Cofactors are inorganic, coenzymes are organic
Explanation: Cofactors are typically metal ions, while coenzymes are organic molecules, often derived from vitamins, that assist enzyme function.

8. Which enzyme breaks down lactose into glucose and galactose?
a) Maltase
b) Lactase
c) Sucrase
d) Protease
Answer: b) Lactase
Explanation: Lactase is the enzyme responsible for hydrolyzing lactose, a sugar found in milk, into glucose and galactose.

9. What is the purpose of feedback inhibition in enzymatic pathways?
a) To speed up the reaction
b) To increase enzyme concentration
c) To regulate and maintain balance in the pathway
d) To bind more substrates
Answer: c) To regulate and maintain balance in the pathway
Explanation: Feedback inhibition occurs when the end product of a pathway inhibits an earlier enzyme, preventing overproduction.

10. Which enzyme functions in the breakdown of hydrogen peroxide?
a) Amylase
b) Catalase
c) Lipase
d) Urease
Answer: b) Catalase
Explanation: Catalase catalyzes the decomposition of hydrogen peroxide into water and oxygen, protecting cells from oxidative damage.

11. Enzymes that catalyze the same reaction but differ in structure are called?
a) Apoenzymes
b) Isoenzymes
c) Holoenzymes
d) Metalloenzymes
Answer: b) Isoenzymes
Explanation: Isoenzymes (or isozymes) are different molecular forms of an enzyme that catalyze the same reaction but differ in structure and regulatory properties.

12. Which enzyme is used in the process of converting RNA into DNA?
a) DNA polymerase
b) Reverse transcriptase
c) RNA polymerase
d) Ligase
Answer: b) Reverse transcriptase
Explanation: Reverse transcriptase is used by retroviruses to synthesize DNA from an RNA template.

13. What happens when an enzyme reaches saturation with its substrate?
a) The enzyme stops functioning
b) The rate of reaction decreases
c) The rate of reaction remains constant at maximum speed
d) The enzyme denatures
Answer: c) The rate of reaction remains constant at maximum speed
Explanation: Saturation occurs when all enzyme molecules are bound to substrate molecules, and the reaction rate plateaus.

14. Which vitamin is a precursor for the coenzyme NAD⁺?
a) Vitamin B1
b) Vitamin B2
c) Vitamin B3
d) Vitamin B6
Answer: c) Vitamin B3
Explanation: Vitamin B3 (niacin) is a precursor for the coenzyme NAD⁺, which plays a crucial role in metabolic reactions.

15. How do non-competitive inhibitors affect enzyme activity?
a) They block the active site
b) They bind to the active site and compete with the substrate
c) They change the enzyme’s shape by binding elsewhere
d) They increase substrate concentration
Answer: c) They change the enzyme’s shape by binding elsewhere
Explanation: Non-competitive inhibitors bind to a different site on the enzyme, altering its structure and reducing its activity.