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. Watson and Crick had access to X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins. This data provided critical evidence about the helical structure of DNA, including the spacing between the bases and the overall dimensions of the helix.
2. They utilized Chargaff's rules, which stated that the amount of adenine (A) equals the amount of thymine (T), and the amount of cytosine (C) equals the amount of guanine (G). This suggested base pairing as a key feature of DNA structure.
3. Watson and Crick used model-building techniques to test different possible structures of DNA. They constructed physical models to visualize how the molecular components could fit together in a stable configuration.
4. They hypothesized that DNA is a double helix with two strands running in opposite directions (antiparallel) and that the bases are paired in the interior of the helix, held together by hydrogen bonds (A pairs with T, and C pairs with G).
5. Their approach combined experimental evidence (from Franklin and Wilkins) with theoretical reasoning and model-building, leading to the proposal of the double-helix structure, which explained both the physical properties of DNA and its role in genetic information storage and replication.

Key Concepts

Double Helix Structure

The double helix is the three-dimensional structure of DNA, consisting of two intertwined strands that form a spiral shape. This model, proposed by Watson and Crick in 1953, illustrates how the sugar-phosphate backbone of each strand runs in opposite directions, allowing for complementary base pairing between adenine-thymine and guanine-cytosine. Understanding this structure is crucial for grasping how genetic information is stored and replicated.

X-ray Crystallography

X-ray crystallography is a technique used to determine the atomic and molecular structure of a crystal by diffracting X-ray beams through it. Rosalind Franklin's X-ray diffraction images of DNA provided critical evidence of its helical structure, which was pivotal for Watson and Crick's model. This method allowed them to visualize the dimensions and arrangement of the DNA molecule, supporting their hypothesis about its structure.

Base Pairing Rules

Base pairing rules refer to the specific pairing of nitrogenous bases in DNA, where adenine pairs with thymine and guanine pairs with cytosine. This complementary pairing is essential for DNA replication and transcription, ensuring that genetic information is accurately copied and expressed. Watson and Crick's understanding of these rules was fundamental in constructing their model of DNA, as it explained how the two strands could be held together and how genetic information could be reliably transmitted.