# DBT JRF 2020 — Question 45

Exam: DBT JRF 2020 · Section: A · Topic: Molecular Biology · Difficulty: Medium

## Question

Denaturation of DNA is a

## Options

- **A.** cooperative phenomenon
- **B.** linear process
- **C.** neither linear nor a cooperative process
- **D.** temperature-independent process

## Answer

Option A

## Explanation

DNA denaturation (melting) is a cooperative (sigmoidal) process. Once initial base pairs break, adjacent base pairs become destabilised because: (1) stacking interactions between adjacent bases are disrupted, and (2) the helix is locally unwound, reducing the thermodynamic cost of further melting. This positive cooperativity produces a sharp melting curve with a well-defined melting temperature ( $T_m$ ) — the temperature at which 50% of DNA is single-stranded. The $T_m$ is higher for GC-rich sequences (3 H-bonds per GC pair vs. 2 for AT). The sigmoidal (not linear) shape proves the cooperative nature of DNA melting.

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