Virology investigation history

1. Experiments

2. Griffith’sExperiment Performed by aBritish bacteriologist Frederick Griffith in
1928.
Experiments involved Streptococcus pneumoiae and mice.
Griffith wastrying to develop vaccineagainstpneumonia.
Twostrains of bacteria were used, roughand smooth. Mice
injected with live roughbacteria were not sick,hencerough
S. pneumoniae is not virulent.
However, smoothstrain of S. pneumoniae caused
pneumonia in mice.Thisis due to the presence of
polysaccharide coat of smooth S. pneumoniae which
protected live S. pneumoniae from mice immunesystem.
Then, Griffith heat-killed smoothS. pneumoniae and injected
mice with it, asexpected mice did not get pneumonia this
time.
Surprisehappened when mice were injected with mixture of
live roughand heat-killed smoothbacteria. Subsequently
,
mice developed pneumonia and died. When blood sample
from dead mice were taken, live smooth S. pneumoniae
were found!
Griffithcalled this ‘transforming principle’, which allowed
rough bacteria to becomesmooth andvirulent.
ImagefromKhanacademy

3. Experiments by Avery,McCartyand MacLeod
in 1944
• Although Griffith’s experiments wereseminal
in establishing importance of genetic
material, it did not show what was
responsible for the geneticinformation.
• Avery andcoset out to figure out thecritical
molecule in S. pneumoniae that was
transforming roughS.pneumoniae into viral
smoothbacteria.
• Theygot rid of lipids andpolysaccharades
from the heat-killed smoothbacteria.
• Thentreated some remainders of smooth
bacteria with protease, somewith DNaseand
somewith RNase.Thenadded rough
bacteria, and observed that only fractions
with DNasetreatment were unable to
become smoothbacteria.
• Thishasestablished that DNAis the genetic
material, however, scientific community was
reluctant to accept DNAasthe carrier of
genetic information.
Imagefrombioninja

4. Hershey – Chase experiments
• In an attempt to further confirm that it is
DNAthat is the genetic material, Hershey
and co studied bacteriophages and
bacteria.
• It was known to them thatphage attaches
itself onto the surface of the bacteria and
releases either DNAor protein, following
which those ‘instructions’ makebacteria
produce phage.
• Distinct batches of phageswere produced
in the presence of either 35Sor 32P,
radioactive isotopes of Sand P
.Since
proteins contain S,they were labeled with
35S.While DNAcontain Pand 32Pwas
incorporated into DNAmolecules.
• Bacteria were infected with the labeled
phage, and following infection phage and
bacteria were separated.
• Bymeasuring the radioactivity DNAfound
to be inside the bacteria, while protein
stayed outside. Thisexperiments
confirmed that DNAwas the genetic
molecule.
Imagefrom openstaxbiology

5. Boyer-Cohen collaborationlaidthe foundationsfor
development of recombinant technology and of
biotechindustry
• In 1972 both Boyerand Cohenhappened to be inameetingon plasmids in
Hawaii.
• While Boyerpresented his work on the digestionof DNAby EcoRI,Cohen
presented his work on the discoveryof the methodby which bacteria
could take up aplasmid.
• Two started a collaboration which led to significant advances in the field.
Their work laid the foundation for recombinant technology and biotech in
general.
• Later Boyerco-foundedthe biotech giant Genentech,which is now part of
Roche.Rocheacquired Genentech for $46.8 billion.
• While in Genentech,Boyer and corecombinantly produced Humulin, a
human insulin, which wasapproved by FDAin 1982.