History of DNA

Erwin Chargaff’s DNA Data

1. What observations can you make about the data in the following table? What patterns do you notice? 2. What does the data show about the make-up of the DNA for different species?

Nitrogenous Base Make-Up of Different Organism’s DNA (in %) C Mycobacterium tuberculosis 15.1 14.6 34.9 35.4 Yeast 31.3 32.9 18.7 17.1 Wheat 27.3 27.1 22.7 22.8 Sea Urchin 32.8 32.1 17.7 17.3 Marine Crab 47.3 2.7 Turtle 29.7 27.9 22.0 21.3 Rat 28.6 28.4 21.4 21.5 Human 30.9 29.4 19.9 19.8

What observations can you make about the data in the table What observations can you make about the data in the table? What patterns do you notice? The amount of A is almost equal to the amount of T, the amount of G is almost equal to the amount of C. This is because A pairs with T, G pairs with C. 2. What does the data show about the make-up of the DNA for different species? Different species have different amounts of A, T, G, and C. This is what makes them different.

Purine and Pyrimidine What can you conclude about the purine :pyrimidine ratio of DNA?

Purine and Pyrimidine What can you conclude about the purine :pyrimidine ratio of DNA? 1:1 ratio Each purine bonds with one pyrimidine.

This 1:1 ratio is important because there are always three rings across, 1 purine (2 rings) bonded with 1 pyrimidine (1 ring) this allows DNA to have a straight ladder shape that can be twisted into a double helix, if it weren’t always 3 rings across, it would break when twisted.

Discovery of the Structure of DNA Rosalind Franklin (click Watch Preview) http://www.pbs.org/wgbh/nova/photo51/ James Watson and Francis Crick (click pieces of the puzzle and Watson’s base pairing) http://www.dnai.org/a/index.html

Discovery of the Structure of DNA Rosalind Franklin Took the first x-ray photo of DNA James Watson and Francis Crick Discovered the structure of DNA