Which of the following is a palindromic sequence ?

Options

A. `5'-CGTATG -3'`
`5'- GCATAC-3'`
B. `5' - CG"AA"TG - 3'`
`3' -CG"AA"TG-5'`
C. `5' - G"AA"TTC - 3' `
`3' - CTT"AA"G - 5'`
D. `5' - GACTAC - 3' `
`3' - TACGAC - 5'`

Answer

To determine which of the provided sequences is a palindromic sequence, we need to understand what a palindromic sequence is. A palindromic sequence is one that reads the same forwards and backwards when considering the complementary strands of DNA.

### Step-by-step Solution:

1. **Understand the Definition**:
- A palindromic sequence in DNA is a sequence that is identical when read from the 5' to 3' direction on one strand and from the 3' to 5' direction on the complementary strand.

2. **Analyze Each Option**:
- We will check each option one by one to see if it meets the criteria of being palindromic.

3. **Option 1**:
- Given sequence: **GTA TGC**
- Complementary sequence (reverse): **GCA TAC**
- Check: The complementary sequence does not match the original sequence when read in reverse.
- Conclusion: **Not a palindromic sequence.**

4. **Option 2**:
- Given sequence: **CGA ATG**
- Complementary sequence (reverse): **CAT TCG**
- Check: The complementary sequence does not match the original sequence when read in reverse.
- Conclusion: **Not a palindromic sequence.**

5. **Option 3**:
- Given sequence: **GAA TCT**
- Complementary sequence (reverse): **AGA TTC**
- Check: The complementary sequence matches the original sequence when read in reverse.
- Conclusion: **This is a palindromic sequence.**

6. **Option 4**:
- Given sequence: **GAC TAC**
- Complementary sequence (reverse): **GTA CTG**
- Check: The complementary sequence does not match the original sequence when read in reverse.
- Conclusion: **Not a palindromic sequence.**

7. **Final Conclusion**:
- The only palindromic sequence from the given options is **Option 3: GAA TCT**.