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

Options

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

Answer

To answer the question "Which of the following bonds are formed by the action of DNA ligase?", we can follow these steps:

### Step 1: Understand the Role of DNA Ligase
DNA ligase is an enzyme that plays a crucial role in DNA replication and repair. Its primary function is to join two DNA fragments together.

### Step 2: Identify the Bonds Formed
When DNA ligase acts on DNA, it facilitates the formation of bonds between the 3' hydroxyl group of one nucleotide's sugar and the 5' phosphate group of another nucleotide's sugar. This results in the formation of a specific type of bond.

### Step 3: Determine the Type of Bond
The bond that is formed between the sugar of one nucleotide and the phosphate of another nucleotide is known as a **phosphodiester bond**. This bond is crucial for linking nucleotides together in a DNA strand.

### Step 4: Analyze the Options
The options given in the question are:
1. Sugar phosphate bond
2. Phosphodiester bond
3. Phosphate phosphate bond
4. Both 1 and 2

From our understanding:
- The **sugar phosphate bond** can refer to the connection between the sugar and phosphate in a nucleotide, but it's more accurately described as a phosphodiester bond when discussing the linkage between nucleotides.
- The **phosphodiester bond** is indeed formed by the action of DNA ligase.
- The **phosphate phosphate bond** is not formed by DNA ligase.

### Step 5: Conclusion
Based on the analysis, the correct answer is that DNA ligase forms the **phosphodiester bond** and can also be associated with the sugar-phosphate bond in the context of nucleotide connections. Therefore, the correct option is **both 1 and 2**.

### Final Answer
The answer to the question is **D: Both 1 and 2**.

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