Rosalind Franklin’s X-ray diffraction studies of DNA revealed two distinct structural forms depending on hydration. Which two forms did she identify?

• A. A-DNA and Z-DNA
• B. C-DNA and D-DNA
• C. B-DNA and Z-DNA
• D. A-DNA and B-DNA

Answer: (D)

Verified step by step guidance

1. Understand that Rosalind Franklin's X-ray diffraction studies focused on the structural forms of DNA under different hydration conditions.
2. Recall that DNA can exist in multiple conformations, but the two most common forms identified in early studies are A-DNA and B-DNA.
3. Recognize that B-DNA is the hydrated, biologically active form typically found in cells, while A-DNA is a more compact form that appears under dehydrated conditions.
4. Note that Franklin's X-ray diffraction patterns showed distinct differences between these two forms, allowing her to identify both A-DNA and B-DNA.
5. Conclude that the two forms identified by Franklin are A-DNA and B-DNA, which correspond to different hydration states of the DNA molecule.