# DBT JRF 2020 — Question 47

Exam: DBT JRF 2020 · Section: A · Topic: Biochemistry · Difficulty: Easy

## Question

While working in the lab, you forgot to keep enzymes back in the fridge. Which of the following enzyme will be least affected on being left outside at room temperature?

## Options

- **A.** BamHI restriction enzyme
- **B.** Topoisomerase
- **C.** Taq DNA polymerase
- **D.** DNA ligase

## Answer

Option C

## Explanation

Taq DNA polymerase is isolated from Thermus aquaticus, a thermophilic bacterium that thrives in hot springs at 70–75°C. It is inherently thermostable (optimal activity at ~72°C, stable up to 95°C) because its proteins have evolved to maintain structure at high temperatures through increased hydrophobic interactions, salt bridges, and reduced flexible loops. At room temperature (~25°C), Taq is far from its denaturation point. In contrast, BamHI (optimal 37°C), topoisomerase, and DNA ligase (optimal 25–37°C) are mesophilic enzymes that lose activity at non-optimal temperatures.

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