Generally the palindromic sequence in dsDNA at which restriction enzymes act and cut into small segments contain

Options

A. Always 4 base pairs only
B. Always 6 base pairs only
C. Always 5 pairs only
D. 4 to 6 base pairs

Answer

To solve the question regarding the palindromic sequence in double-stranded DNA (dsDNA) at which restriction enzymes act, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Restriction Enzymes**:
- Restriction enzymes, also known as restriction endonucleases, are proteins that cut DNA at specific sequences. These sequences are known as restriction sites.

2. **Identify the Nature of Restriction Sites**:
- The restriction sites are typically palindromic sequences, meaning that the sequence of bases reads the same in the 5' to 3' direction on one strand and in the 5' to 3' direction on the complementary strand.

3. **Determine the Length of Palindromic Sequences**:
- The question asks about the length of these palindromic sequences. Restriction sites can vary in length.

4. **Examine Common Lengths of Palindromic Sequences**:
- Most restriction enzymes recognize and cut at specific palindromic sequences that are typically 4 or 6 base pairs long.
- For example:
- EcoRI recognizes the sequence GAATTC, which is 6 base pairs long.
- A restriction enzyme like HaeIII recognizes the sequence GGCC, which is 4 base pairs long.

5. **Conclude the Possible Lengths**:
- Based on the information about restriction enzymes and their recognition sites, we conclude that the palindromic sequences can contain either 4 or 6 base pairs.

6. **Select the Correct Answer**:
- Therefore, the correct answer to the question is "four to six base pairs."

### Final Answer:
The palindromic sequence in dsDNA at which restriction enzymes act and cut into small segments contains **four to six base pairs**.

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