One strand of double helix of DNA reads 5'-AAA T TCGA-3'. Which of the following strands can form double helix?

Options

A. 5' - TTT AAGCT- 3'
B. 3'-T TT AA GCT - 5
C. 5'-T TT AACGA-3'
D. 3'-T TTAA CGA-3

Explanation

To determine which strand can form a double helix with the given DNA strand 5'-AAATTCGA-3', we need to find its complementary strand based on the base pairing rules of DNA.

### Step-by-Step Solution:

1. **Identify the Given Strand**:
The provided DNA strand is 5'-AAATTCGA-3'.

2. **Understand Base Pairing Rules**:
- Adenine (A) pairs with Thymine (T)
- Thymine (T) pairs with Adenine (A)
- Cytosine (C) pairs with Guanine (G)
- Guanine (G) pairs with Cytosine (C)

3. **Determine the Complementary Bases**:
- The complementary bases for the given strand are:
- A (Adenine) → T (Thymine)
- A (Adenine) → T (Thymine)
- A (Adenine) → T (Thymine)
- T (Thymine) → A (Adenine)
- T (Thymine) → A (Adenine)
- C (Cytosine) → G (Guanine)
- G (Guanine) → C (Cytosine)
- A (Adenine) → T (Thymine)

4. **Write the Complementary Strand**:
- The complementary sequence to 5'-AAATTCGA-3' is 3'-TTTAAGCT-5'.

5. **Reverse the Complementary Strand for Proper Orientation**:
- Since DNA strands run in opposite directions (antiparallel), we need to write the complementary strand in the 5' to 3' direction:
- The 3'-TTTAAGCT-5' strand will be written as 5'-TCGAATTT-3'.

6. **Check the Options**:
- Now, we need to compare the complementary strand (5'-TCGAATTT-3') with the provided options to find the correct match.

### Conclusion:
The strand that can form a double helix with the given strand 5'-AAATTCGA-3' is 5'-TCGAATTT-3'.