Dna Replication

Step 1: Understanding Chargaff's rule.
According to Chargaff's rule, in a double-stranded DNA molecule: and Thus, the sum of adenine and thymine is equal to the sum of guanine and cytosine: Step 2: Calculating the percentage of guanine.
Given that adenine constitutes 30% of the bases, thymine must also constitute 30%: This leaves 40% for guanine and cytosine: Since the amount of guanine equals the amount of cytosine: Step 3: Conclusion.
The percentage of guanine in the DNA molecule is 20%.

Statement 1: Avery, McLeod, and McCarty discovered the semi-conservative nature of DNA.

Statement 2: Meselson and Stahl used E. coli to demonstrate the semi-conservative nature of DNA.

Analysis:

• Statement 1 is incorrect. Avery, McLeod, and McCarty demonstrated that DNA, not protein, is the genetic material. They did not discover the semi-conservative nature of DNA replication.
• Statement 2 is correct. Meselson and Stahl conducted experiments using E. coli and isotopes of nitrogen to prove that DNA replication is semi-conservative.

Therefore, the correct answer is:

Option 2: Statement 2 is correct, Statement 1 is incorrect