What evidence did Watson and Crick have at their disposal in 1953? What was their approach in arriving at the structure of DNA?

Verified step by step guidance

1. Understand the historical context: In 1953, James Watson and Francis Crick were working on understanding the structure of DNA, which was known to be the molecule responsible for heredity.
2. Review the key evidence: They had access to X-ray diffraction images of DNA, particularly the famous 'Photo 51' taken by Rosalind Franklin and Raymond Gosling, which suggested a helical structure.
3. Consider Chargaff's rules: Erwin Chargaff had discovered that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C), suggesting base pairing.
4. Analyze the model-building approach: Watson and Crick used model-building techniques to hypothesize the double helix structure, where two strands of DNA run in opposite directions and are held together by base pairs (A-T and G-C).
5. Synthesize the information: By combining the X-ray diffraction data, Chargaff's rules, and their model-building, Watson and Crick proposed the double helix structure of DNA, which explained how genetic information is stored and replicated.

Key Concepts

Double Helix Structure

Watson and Crick proposed that DNA has a double helix structure, consisting of two intertwined strands. This model explained how genetic information is stored and replicated, with the strands running in opposite directions and held together by complementary base pairing between adenine-thymine and guanine-cytosine.

X-ray Crystallography

X-ray crystallography was a critical technique used by Rosalind Franklin, whose images of DNA provided key insights into its helical structure. Watson and Crick utilized these images, particularly the famous Photo 51, to infer the dimensions and arrangement of the DNA molecule, which was pivotal in their model development.

Base Pairing Rules

The base pairing rules, established by Erwin Chargaff, state that in DNA, the amount of adenine equals thymine, and the amount of guanine equals cytosine. This concept was essential for Watson and Crick as it guided them in understanding how the two strands of DNA are complementary, allowing for accurate replication and transmission of genetic information.