Which of the following reactions is not enzyme-mediated in biological system ?

Options

A. Dissolving `CO_(2)` in water
B. Unwinding the two strands of DNA
C. Hydrolysis of sucrose
D. Formation of peptide bond

Explanation

To determine which of the following reactions is not enzyme-mediated in biological systems, we will analyze each option provided:

1. **Dissolving CO2 in water**: This process involves the physical interaction of carbon dioxide gas with water, leading to the formation of carbonic acid. This reaction occurs naturally and does not require any enzyme to facilitate it. Therefore, this reaction is not enzyme-mediated.

2. **Unwinding the two strands of DNA**: This process is essential for DNA replication and transcription. It is facilitated by the enzyme topoisomerase, which helps to relieve the tension in the DNA strands as they unwind. Thus, this reaction is enzyme-mediated.

3. **Hydrolysis of sucrose**: This reaction involves the breakdown of sucrose into glucose and fructose. It is catalyzed by the enzyme sucrase (or invertase). Therefore, this reaction is also enzyme-mediated.

4. **Formation of peptide bonds**: Peptide bonds are formed during protein synthesis, and this process is facilitated by the enzyme peptidyltransferase. Hence, this reaction is enzyme-mediated as well.

After analyzing all the options, we conclude that the reaction that is not enzyme-mediated is:

**Correct Answer: Dissolving CO2 in water**