Which of the following could be a restriction enzyme recognition site ?

Options

A. ATGCAT
B. ATCATC
C. AAGGA
D. ATCCTA

Answer

To determine which of the given sequences could be a restriction enzyme recognition site, we need to identify if any of the sequences are palindromic. A palindromic sequence reads the same forwards and backwards when considering complementary base pairing.

### Step-by-Step Solution:

1. **Understand the Concept of Palindromic Sequences**:
- A palindromic sequence is one that reads the same in both directions when considering base pairing. For DNA, this means that if you read the sequence from the 5' to 3' direction, it should match the complementary sequence read from the 3' to 5' direction.

2. **Analyze Each Sequence**:
- **Sequence 1: ATGCAT**
- Complementary sequence: TACGTA
- Forward: ATGCAT
- Backward (complementary): TACGTA
- This is a palindromic sequence.

- **Sequence 2: ATCATC**
- Complementary sequence: TAGTAG
- Forward: ATCATC
- Backward (complementary): TAGTAG
- This is a palindromic sequence.

- **Sequence 3: AAGGA**
- Complementary sequence: TTCC
- Forward: AAGGA
- Backward (complementary): TTCC
- This is not a palindromic sequence.

- **Sequence 4: ATCCTA**
- Complementary sequence: TAGGAT
- Forward: ATCCTA
- Backward (complementary): TAGGAT
- This is not a palindromic sequence.

3. **Identify the Correct Answer**:
- From the analysis, **Sequence 1 (ATGCAT)** and **Sequence 2 (ATCATC)** are palindromic sequences and could serve as restriction enzyme recognition sites.

### Conclusion:
The correct answer is that the first sequence (ATGCAT) is a palindromic sequence and could be a restriction enzyme recognition site.