Question

Q1. Discovering the Structure of DNA.  Jim Watson and Francis Crick were able to build the correct model of DNA based on four key pieces of information that they learned from the work of Rosalind Franklin, Erwin Chargaff and others.  List the four key pieces of information that led to the correct model. Write on back of page if you need to. (this is for genetics)

Answer 1

Four key pieces of information that led to correct model of DNA structure by Watson and Crick are:

1. Chargaff's data that conveys that DNA from any cell of any organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases. In other words, the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine.

2. Rosalind Franklin's high resolution X-ray diffraction patterns of DNA confirming that the structure of DNA is right handed double helix and is anti-parellel with the two sugar-phosphate backbones lying on the outside. .

3. The incorporation of corrected base structures (helped by Donohue) inside the helical core and modeling the phosphate structures outside helped them to demonstrate hydrogen bonding between nitrogen bases of the adjacent DNA strands which accounted Chargaff's rule (A only pairs with T with two hydrogen bonds and G only pairs with C with three hydrogen bonds between them) and how the two helical strands were held together by base pairing.

4. Building the physical model of DNA structure (ball and stick model which was inspired by Linus Pauling) and proposing a logic conclusion of copying mechanism in which the double strands separate and each separated strand will serve as the template for making another new strand (Semi-conservative replication).