Practice Enzymes MCQs for AKU Entry Test Biology — topic-wise sets with solved answers.
Q1. A biochemical reaction requires a specific amount of energy to initiate the breaking of chemical bonds. This energy requirement is known as:
Answer: Activation energy
Explanation: Activation energy is the minimum barrier for reactions; kinetic energy merely describes particle motion and lacks the specific initiation threshold.
Q2. In many enzymatic reactions, metal ions like magnesium or iron are required to detach easily from the protein part. These are called:
Answer: Activators
Explanation: Activators are inorganic metallic ions like Mg2+; coenzymes are organic molecules, often vitamin derivatives, which serve a different structural role.
Q3. The catalytic activity of an enzyme is restricted to a small region containing specific amino acids that determine its shape. This region is:
Answer: Active site
Explanation: The active site facilitates catalysis; the allosteric site is a separate regulatory region where non-competitive inhibitors or activators typically bind.
Q4. An enzyme like urease only acts upon urea and no other substrate, even those with similar structures, demonstrating a high degree of:
Answer: Substrate specificity
Explanation: Substrate specificity refers to an enzyme acting on one molecule; reaction specificity describes the type of chemical change occurring regardless of substrate.
Q5. In a metabolic pathway, the end product binds to the first enzyme to stop the production sequence. This regulatory mechanism is called:
Answer: Feedback inhibition
Explanation: Feedback inhibition regulates pathways via the end product; irreversible inhibition permanently destroys enzyme activity through covalent bonding at active sites.
Q6. A non-protein part that is permanently and covalently bonded to the enzyme's protein structure is specifically defined as a:
Answer: Prosthetic group
Explanation: Prosthetic groups are permanently attached non-protein components; coenzymes are loosely attached organic molecules that easily dissociate after the catalytic reaction.
Q7. Many enzymes utilize derivatives of vitamins like NAD or FAD to transport chemical groups or electrons. These organic molecules are:
Answer: Coenzyme
Explanation: Coenzymes are organic carriers like NAD; activators are inorganic metal ions, which underprepared students often confuse with organic cofactors.
Q8. Malonic acid resembles succinic acid and competes for the active site of succinate dehydrogenase. This type of interaction is called:
Answer: Competitive inhibition
Explanation: Competitive inhibitors like malonate mimic the substrate's shape; non-competitive inhibitors bind elsewhere, failing to resemble the substrate's molecular structure.
Q9. When the essential non-protein part is removed from an enzyme, the remaining inactive protein part is known as the:
Answer: Apoenzyme
Explanation: An apoenzyme is the inactive protein part; a holoenzyme is the complete, active complex including the required cofactor or prosthetic group.
Q10. During the formation of the enzyme-substrate complex, the substrate undergoes a high-energy, unstable state before becoming products. This is the:
Answer: Transition state
Explanation: The transition state is the unstable mid-point of a reaction; the product state represents the final stable molecules after catalysis completes.
Q11. Enzymes in the human body generally reach their maximum rate of reaction at which specific temperature according to PTB?
Answer: 37 degrees Celsius
Explanation: Human enzymes function optimally at 37 degrees Celsius; 25 degrees is standard room temperature and results in lower kinetic energy for collisions.
Q12. The enzyme pepsin, which functions in the acidic environment of the stomach, has an optimum pH value of:
Answer: 2.0
Explanation: Pepsin requires a highly acidic pH of 2.0; a neutral pH of 7.0 would denature the enzyme and stop its activity.
Q13. Cyanide combines with the iron of cytochrome oxidase at a site other than the active site, blocking respiration. This is:
Answer: Non-competitive inhibition
Explanation: Non-competitive inhibitors bind to separate sites; competitive inhibitors must resemble the substrate to occupy the active site, which cyanide does not.
Q14. The hypothesis suggesting that the active site is flexible and molds around the substrate for a better fit was proposed by Koshland:
Answer: Induced fit model
Explanation: The induced fit model describes active site flexibility; the lock and key model incorrectly assumes a rigid, unchanging active site structure.
Q15. When all active sites are occupied by substrate molecules, further increasing substrate concentration does not increase the rate. This state is:
Answer: Saturation
Explanation: Saturation occurs when all active sites are busy; denaturation involves the physical unfolding of the protein due to heat or pH.
Q16. Enzymes involved in the process of cellular respiration and ATP production are specifically localized within which organelle?
Answer: Mitochondria
Explanation: Respiratory enzymes are localized in mitochondria; ribosomes are the site of protein synthesis and do not contain the Krebs cycle enzymes.
Q17. Emil Fischer proposed a model in 1894 where the enzyme and substrate have rigid, complementary shapes. This model is:
Answer: Lock and key model
Explanation: The lock and key model emphasizes rigid complementarity; the induced fit model is more accurate as it accounts for conformational changes.
Q18. The specific part of the active site that transforms the substrate into products by breaking and forming bonds is the:
Answer: Catalytic site
Explanation: The catalytic site performs the chemical transformation; the binding site's role is limited to orienting and holding the substrate in place.
Q19. A fully functional enzyme consisting of both an apoenzyme and its required cofactor is referred to as a:
Answer: Holoenzyme
Explanation: A holoenzyme is the complete functional unit; an apoenzyme is only the protein portion and lacks its necessary non-protein cofactor.
Q20. Exposure to extremely high temperatures causes the loss of the three-dimensional shape of an enzyme, rendering it permanently non-functional. This is:
Answer: Denaturation
Explanation: Denaturation is the irreversible loss of tertiary structure; inactivation might be reversible and doesn't necessarily involve the unfolding of the protein.
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