Enzyme Activity & Tertiary Structure — NEET Biology
📚 Practice ConceptThe activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein. These include temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity.
Which of the above statements are correct? S1: Enzymes generally function optimally within a narrow range of temperature and pH, with activity declining sharply outside this range. S2: At temperatures significantly above the optimum, enzymes undergo denaturation, which permanently destroys their catalytic activity. S3: Low temperatures temporarily inactivate enzymes, preserving their structure and allowing them to regain activity upon temperature increase. S4: The maximum velocity (Vmax) of an enzyme-catalyzed reaction can be continuously increased by further raising the substrate concentration. S5: Competitive inhibitors structurally resemble the natural substrate and bind to the enzyme's active site, thereby blocking substrate access. S6: Enzymes isolated from organisms adapted to extremely high temperatures typically lose their catalytic power above 40°C.
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Correct answer: B — S1, S2, S3 and S5 only
The activity of an enzyme is highly sensitive to conditions such as temperature, pH, substrate concentration, and inhibitors. S1: Correct. Enzymes show their highest activity at an optimum temperature and pH. Activity declines both below and above these optimum values. S2: Correct. High temperatures (typically above 40°C for most enzymes) cause denaturation of the enzyme protein, leading to a permanent loss of catalytic activity. S3: Correct. Low temperature preserves the enzyme in a temporarily inactive state, meaning its structure is maintained, and it can regain activity when conditions become optimal again. S4: Incorrect. With increasing substrate concentration, the velocity of the enzymatic reaction rises initially but eventually reaches a maximum velocity (Vmax). At Vmax, all enzyme active sites are saturated with substrate, and no further increase in velocity occurs even with more substrate. S5: Correct. Competitive inhibitors are chemicals that closely resemble the substrate in molecular structure and compete with the substrate for binding to the enzyme's active site, thus inhibiting enzyme activity. S6: Incorrect. Enzymes isolated from thermophilic organisms (e.g., those living in hot vents and sulphur springs) are stable and retain their catalytic power even at very high temperatures (up to 80°-90°C), demonstrating thermal stability. Therefore, statements S1, S2, S3, and S5 are correct. The final answer is B.
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