The number of covalent bonds formed during the formation of r - DNA .

Options

A. 2
B. 3
C. 4
D. 1

Answer

To determine the number of covalent bonds formed during the formation of recombinant DNA (r-DNA), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Recombinant DNA Formation**:
- Recombinant DNA is formed by combining DNA from two different sources. This process typically involves cutting the DNA at specific sites and then joining the fragments together.

2. **Role of Ligase Enzyme**:
- The enzyme responsible for joining the DNA fragments is called DNA ligase. This enzyme facilitates the formation of covalent bonds between the DNA fragments.

3. **Types of Bonds Formed**:
- The covalent bonds that are formed during this process are specifically known as phosphodiester bonds. These bonds occur between the phosphate group of one nucleotide and the deoxyribose sugar of another nucleotide.

4. **Counting the Covalent Bonds**:
- When two DNA fragments are ligated, each fragment will contribute to the formation of a bond. For example, if we have two fragments, we will create one bond between them.
- If we consider the process of forming a recombinant DNA molecule from two fragments, we can visualize that:
- For two fragments, one bond is formed.
- For three fragments, two bonds are formed.
- For four fragments, three bonds are formed.
- Thus, if we are forming a recombinant DNA molecule from two different DNA sources, we will typically form three covalent bonds.

5. **Conclusion**:
- Therefore, the total number of covalent (phosphodiester) bonds formed during the formation of recombinant DNA is **3**.

### Final Answer:
The number of covalent bonds formed during the formation of recombinant DNA is **3**.