Melting of DNA at `70^(@)C` is due to breakdown of

Options

A. Phosphodiester bonds
B. Hydrogen bonds
C. Glycosidic bonds
D. Disulphide bonds

Answer

To solve the question regarding the melting of DNA at 70°C, we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of DNA Melting**:
- DNA melting refers to the process where double-stranded DNA separates into single strands. This process is also known as denaturation.

2. **Identify the Bonds in DNA**:
- DNA is held together by various types of bonds:
- **Phosphodiester Bonds**: These bonds link the sugar and phosphate groups in the DNA backbone.
- **Hydrogen Bonds**: These bonds form between the complementary nitrogenous bases (A-T and C-G).
- **Glycosidic Bonds**: These bonds connect the nitrogenous bases to the sugar molecule.
- **Disulfide Bonds**: These are not present in DNA; they are more relevant in protein structures.

3. **Determine the Temperature Effect**:
- When DNA is heated, the temperature affects the stability of the bonds. The melting temperature (Tm) is influenced by the number of hydrogen bonds between the strands.

4. **Analyze the Bonds Under Heat**:
- At 70°C, the primary bonds that break are the hydrogen bonds. These bonds are weaker compared to phosphodiester bonds, which are covalent and much stronger.

5. **Conclude the Answer**:
- Since the question asks about the breakdown that leads to melting, and considering that hydrogen bonds are responsible for holding the two strands together, the correct answer is that melting of DNA at 70°C is due to the breakdown of hydrogen bonds.

### Final Answer:
The melting of DNA at 70°C is due to the breakdown of **hydrogen bonds**.

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