Which of the following bonds are formed by the action of DNA ligase ?

Options

A. Sugar-phosphate bond
B. Phosphodiester bond
C. Both (1) and (2)
D. Phosphate-phosphate bond

Answer

To determine which bonds are formed by the action of DNA ligase, we need to analyze the options provided and understand the role of DNA ligase in DNA structure.

### Step-by-Step Solution:

1. **Understanding DNA Ligase**:
- DNA ligase is an enzyme that plays a crucial role in the joining of DNA fragments. It facilitates the formation of bonds between the nucleotides in the DNA strands.

2. **Evaluating the Options**:
- The options given are:
- a) Sugar-phosphate bond
- b) Phosphodiester bond
- c) Both sugar-phosphate bond and phosphodiester bond
- d) Phosphate-phosphate bond

3. **Analyzing Sugar-Phosphate Bond**:
- The term "sugar-phosphate bond" is somewhat misleading. In DNA, the sugar and phosphate groups are part of the backbone structure, but they do not form a distinct bond referred to as a "sugar-phosphate bond." Instead, they are linked through phosphodiester bonds.

4. **Understanding Phosphodiester Bond**:
- A phosphodiester bond is the bond that connects the 5' phosphate group of one nucleotide to the 3' hydroxyl group of another nucleotide. This bond is crucial for forming the DNA backbone and is indeed formed by the action of DNA ligase.

5. **Evaluating Other Options**:
- The option stating "both 1 and 2" is incorrect because the sugar-phosphate bond is not a recognized bond formed during the ligation process.
- The "phosphate-phosphate bond" is also incorrect as such bonds do not occur in the structure of DNA.

6. **Conclusion**:
- Based on the analysis, the only correct bond that is formed by the action of DNA ligase is the **phosphodiester bond**.

### Final Answer:
The bond formed by the action of DNA ligase is the **phosphodiester bond**.

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