DNA was extracted from E.coli. The proportion of cytosine was found to be 30%, then what will be the amount of adenine?

Options

A. 0.6
B. 0.7
C. 0.2
D. 0.4

Answer

To solve the question regarding the amount of adenine in the DNA extracted from E. coli, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Chargaff's Rule**:
Chargaff's rule states that in DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). This means:
- A = T
- G = C

2. **Identify the Given Information**:
We know from the question that the proportion of cytosine (C) is 30%. Therefore:
- C = 30%

3. **Calculate the Amount of Guanine**:
According to Chargaff's rule, since C = 30%, then G must also equal 30%. Thus:
- G = 30%

4. **Calculate the Total Percentage of C and G**:
Now, we can add the percentages of cytosine and guanine:
- C + G = 30% + 30% = 60%

5. **Determine the Remaining Percentage for A and T**:
Since the total percentage of all bases (A, T, C, G) must equal 100%, we can find the combined percentage of adenine and thymine:
- A + T = 100% - (C + G) = 100% - 60% = 40%

6. **Divide the Remaining Percentage Between A and T**:
According to Chargaff's rule, A = T. Therefore, we can divide the remaining 40% equally between adenine and thymine:
- A = T = 40% / 2 = 20%

7. **Final Result for Adenine**:
The amount of adenine (A) is therefore 20%. To express this as a decimal:
- A = 20% = 0.20

### Conclusion:
The amount of adenine in the DNA extracted from E. coli is **0.20**.