Question

In sea urchin DNA, which is double stranded, 10% of the bases are shown to be cytosine (C). Based on this observation, the following were recorded
A. Guanine (G) are 10%
B. Adenine (A) are 40%
C. Thymine (T) are 20%
D. Purines are 50%
E. Purine and pyrimidine are equal
Choose the correct answer from the options given below

• A. A, B, C and D only
• B. A, B, C and E only
• C. A, B, D and E only
• D. A, C, D and E only

Hint:

If you know one base percentage in dsDNA, you can find the other three instantly.
\(A+G\) is always 50% in double-stranded DNA.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question requires the application of Chargaff's Rules of base pairing in double-stranded DNA (dsDNA).

Step 2: Key Formula or Approach:
Chargaff's Rules for dsDNA:
1. \(\text{Adenine (A)} = \text{Thymine (T)}\)
2. \(\text{Guanine (G)} = \text{Cytosine (C)}\)
3. \(\text{Purines (A+G)} = \text{Pyrimidines (T+C)} = 50\%\)
4. \(\text{Total Bases} = A + T + G + C = 100\%\)
Detailed Explanation:

• Given: \(C = 10\%\).

• Calculation of G: Since \(G = C\), \(G = 10\%\). (Statement A is True).

• Total G+C: \(10\% + 10\% = 20\%\).

• Calculation of A+T: \(100\% - 20\% = 80\%\).

• Calculation of Individual A and T: Since \(A = T\), each must be half of 80%. So, \(A = 40\%\) and \(T = 40\%\).
- Statement B says \(A = 40\%\) (True).
- Statement C says \(T = 20\%\) (False, it should be 40%).

• Calculation of Purines (A+G): \(40\% + 10\% = 50\%\). (Statement D is True).

• Purine vs Pyrimidine: In any dsDNA, they must be equal. (Statement E is True).
Final Answer:
Statements A, B, D, and E are correct. Option (C) matches this findings.