Download DNA: Structure and Functions

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