In E. coli DNA has 18% of bases of cytosine. What will be the fraction of adenine?

Options

A. 0.18
B. 0.32
C. 0.36
D. Data insufficient

Explanation

To solve the problem, we need to determine the fraction of adenine (A) in E. coli DNA, given that 18% of the bases are cytosine (C).

### Step-by-Step Solution:

1. **Understand Base Pairing in DNA**:
- In DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C).
- This means that the amount of adenine will be equal to the amount of thymine, and the amount of guanine will be equal to the amount of cytosine.

2. **Identify the Percentage of Cytosine**:
- The problem states that cytosine (C) makes up 18% of the bases in E. coli DNA.

3. **Determine the Percentage of Guanine**:
- Since guanine (G) pairs with cytosine (C), the percentage of guanine will also be 18%.
- Therefore, G = 18%.

4. **Calculate the Total Percentage of C and G**:
- Add the percentages of cytosine and guanine together:
\[ C + G = 18\% + 18\% = 36\% \]

5. **Calculate the Remaining Percentage for A and T**:
- The total percentage of all bases in DNA must equal 100%.
- Thus, the remaining percentage for adenine (A) and thymine (T) is:
\[ 100\% - 36\% = 64\% \]

6. **Divide the Remaining Percentage Equally Between A and T**:
- Since adenine (A) and thymine (T) are equal, we divide the remaining percentage by 2:
\[ A = T = \frac{64\%}{2} = 32\% \]

7. **Convert the Percentage of Adenine to Fraction**:
- To find the fraction of adenine, convert 32% to a decimal:
\[ \frac{32}{100} = 0.32 \]

### Final Answer:
The fraction of adenine in E. coli DNA is **0.32**.

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