Oswald Avery Colin MacLeod Maclyn McCarty 1928

Isolating the Hereditary
Material Continued
Oswald
Avery
Maclyn
McCarty
Colin
MacLeod
1928
1
continued with Griffiths work, first
wanting to replicate it because they
didn't believe it.
took the pathogenic bacteria and
treated it with a protein destroying
enzyme and noticed that
transformation still took place
Took an RNA destoying enzyme and
transformation still took place
took DNA destroying enzyme and
there was NO TRANSFORMATION
concluded that DNA determines cell
function and is responsible for
transformation
many didn't believe
• just four letters?
• this was in prokaryotic cells and
can't provide reliable mechanism for
complex organisms
2
another key discovery was that
somatic cells had twice the DNA as
gametes but gametes and somatic
cells varied in its amount of protein.
Erwin Chargaff
Late 1940's
3
nucleotides are not found in equal
numbers
individual cells from the same species
with have the same composition no
matter their state or environmental
situation
the DNA from any cell of all organisms
should have an expected ratio
%A=%T
%G=%C
Martha
Chase
Alfred
Hershey
1952
4
DNA is the genetic hereditary
material
radio­actively tagged a virus
"bacteriophage" which infects e. coli
5
structure of a virus
contains
Sulfur
contains
phosphorous
virus is non­living
requires a host to replicate
tricks host into copying its DNA and
creating more viruses
6
Radioactive
Phosphorous in
DNA non­
radioactive
protein coat
Non­radioactive
DNA and
radioactive
Sulfur in protein
coat
Now we know that DNA is the
hereditary material but we still need
to know how it is structured........
Review Questions page 223
# 1­3, 5­7 and 9
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Attachments
DNAi_chargaff_ratio­lg.mov