The couplings between base units of DNA is through

Options

A. Hydrogen bonding
B. Electrostatic bonding
C. Covalent bonding
D. Vander Waals forces

Answer

To solve the question "The couplings between base units of DNA is through", we need to analyze the types of bonds that connect the base units in DNA. Here is a step-by-step breakdown of the solution:

### Step-by-Step Solution:

1. **Identify the Base Units of DNA**:
- DNA consists of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
- Adenine and guanine are classified as purines, while thymine and cytosine are classified as pyrimidines.

2. **Understand the Pairing of Bases**:
- In DNA, adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G).
- The pairing occurs through specific interactions between the bases.

3. **Determine the Type of Bonding**:
- The connection between adenine and thymine involves two hydrogen bonds.
- The connection between cytosine and guanine involves three hydrogen bonds.
- These interactions are crucial for the stability of the DNA double helix structure.

4. **Evaluate Other Types of Bonds**:
- While there are other types of bonds like covalent bonds, electrostatic interactions, and Van der Waals forces, they are not responsible for the specific pairing of the nitrogenous bases.
- Covalent bonds are involved in the backbone of the DNA (between the sugar and phosphate groups), but not between the bases.

5. **Conclude the Answer**:
- The couplings between the base units of DNA are primarily through **hydrogen bonding**.

### Final Answer:
The couplings between base units of DNA is through **hydrogen bonding**.

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