DNA: Structure and Functions

Genetic Material What we know: Genes are on chromosomes But what are genes made of? Genetic material must be: able to store information Able to be replicated and transmitted from generation to generation Able to undergo mutations - variability

Experiments Miescher – removed nuclei from pus cells, contained nuclein, rich in phosphorus, not sulfur Acidic properties: nucleic acids (DNA, RNA)

Griffith experiment – Transformation in Bacteria 1920 ’ s – vaccine against Streptococcus pneumoniae S strain – smooth, have capsule R strain – rough, no capsule Inject with s-strain, mouse dies Inject with R-strain, mouse lives Inject with heat killed S-strain, mouse lives

Bacterial Transformation

When Griffith took a mixture of the heat-inactivated S strain, mixed with the R strain, the bacteria would die. Thus there was some material in the heat-killed S strain that was responsible for "transforming “ the R strain into a lethal form.

Transformation Taking up of extraneous genetic material from the environment by bacteria

Avery, MacLeod and McCarty Produced paper on proving DNA is the transforming material, using enzymes Enzymes that degrade proteins do not prevent transformation DNase, enzyme that digests DNA, does prevent transformation Molecular weight of genetic material would require thousands of nucleotides which equals genetic variability.

Hershey and Chase – DNA or proteins? Worked with bacteriophages – viruses that infect bacteria Virus consist of genetic material and a protein capsid Used radioactive phosphorous to label the core of the phage and radioactive sulfur to label the protein in the capsid of the phage

Results of Hershey and Chase experiment Viral DNA found in bacteria sediment, viral capsid found in liquid in centrifuged Concluded that viral DNA, not protein, was responsible for directing the production of new viruses

Alfred Hershey and Martha Chase