Biology, Answering the Big Questions of Life/DNA2


Genetic material is DNA Griffith 1928 Pneumococcus Mice injected with S strain die Mice injected with R strain live Kill S and mix it with R before injecting and the mice die

something transferred from the dead S to the R and transformed it.

Avery MacKeod and McCarthy 1944 same system purified extracts of cells by type of macromolecule i.e. destroyed proteins with proteases, removed lipid and carbohydrates, and it still transformed. Transforming principle is DNA

Hershey and chace 1952 Virus that infects bacteria - Bacteriophage T2 Labeled cells with radioactive isotopes Radioactive 35S for the proteins and 32P for the DNA Sheered the phages off of the cells with a Warring blender Looked at what entered the cells.

Supernatant - 35S labeled protein Pellet - bacteria - 32P labeled DNA

DNA entered the cells and caused infection. DNA was the transforming principle. Confirmation

Structure of DNA Rosalind Franklin - Crystallographer - crystlized DNA and took Xray photo - X-ray Crystallography. found repeating spiral pattern.

Chargraff(1950) - biochemist - analyzed DNA and formulated rules of behavior. amount of A always equal to amount of T [A]=[T] amount of C always equal to amount of G [C]=[G]

1953 Watson and Crick model the structure of DNA DNA double helix with bases as rungs of ladder monomer spacing 0.34nm helical spacing 3.4nm per turn (10 bp) Model helped us understand how DNA worked.

Nobel Prize - Watson Crick and Franklin posthumously

(Semi-conservative replication Meselson and Stahl 1957 15N labeled DNA Switch to 14N (normal light) DNA look after one two and three generations

separate by centrifuge

Start - all heavy gen 2 - middle gen 3 middle and light

explain: Strand is half heavy half light Semi-conservative