if one chain of a DNA molecule has the base order 5'ATTGACGT3' . . . . . Then the base order of its complementary chain will be

Options

A. 3' ATTGACGT 5'
B. 5' TGCAGTTA 3'
C. 5' TUUCTGCU 3'
D. 3' TAACTGCA 5'

Answer

To find the base order of the complementary DNA chain for the given sequence 5' ATTGACGT 3', we need to follow these steps:

### Step-by-Step Solution:

1. **Identify the Base Pairing Rules**:
- In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).

2. **Write Down the Given Sequence**:
- The given sequence is 5' ATTGACGT 3'.

3. **Determine the Complementary Bases**:
- For each base in the given sequence, find its complementary base:
- A (from ATTGACGT) pairs with T
- T pairs with A
- T pairs with A
- G pairs with C
- A pairs with T
- C pairs with G
- G pairs with C
- T pairs with A

4. **Construct the Complementary Sequence**:
- Writing down the complementary bases in the same order gives us:
- T (from A)
- A (from T)
- A (from T)
- C (from G)
- T (from A)
- G (from C)
- C (from G)
- A (from T)

5. **Reverse the Order**:
- Since DNA strands are anti-parallel, we need to write the complementary sequence in the reverse order (from 3' to 5'):
- The complementary sequence is 3' TAAC TGCA 5'.

6. **Final Answer**:
- Therefore, the base order of the complementary chain is 3' TAAC TGCA 5'.