Download - PlanbookConnect

15-02-10
Friedrich Miescher
DNA:
The History of Its
Understanding
Mr. Masri
SBI4U
Humberside C.I.
•  Investigated the contents
of pus cell nuclei
•  Pus cells are readily available from
infectious patients.
•  Found that the nuclei contained a
significant amount of material that was
NOT protein
•  Called it nuclein, but it was later named
DNA
Frederick Griffith
•  done in 1928 - tried to develop a vaccine
against pneumoniae
•  worked with 2 types of streptococcus
pneumoniae:
Strain
R (rough)
S (smooth)
Characteristics
•  no capsule
•  non-pathogenic
•  w/ capsule
•  pathogenic
Griffith…
•  Injected different bacteria into four
groups of mice:
Group Mice
Result
#
Injected w/
1
R
Mice lives, unaffected
2
S
Mice die
(from pneumonia)
1
15-02-10
Griffith…
Group Mice
Result
#
Injected w/
3
4
Heat killed S Mice live, unaffected
Heat killed Mice die
S + Live R
•  Blood sample from mice group #4
contained live smooth bacteria
Griffith…
Griffith’s Conclusion:
•  R cells had acquired from the dead S
cells the ability to make the
polysaccharide capsule
•  the bacteria underwent transformation
- the transfer of genetic material from
one bacterium to another through the
liquid in which the bacteria live
2
15-02-10
Griffith…
•  Avery, McCarty and MacCleod (early
1940s) furthered Griffith's work and also
identified DNA as being the transforming
agent
Joachim Hammerling
•  Conducted experiments on
Acetabularia, a one celled green
algae
•  Hypothesized that hereditary
information is stored in the nucleus
Joachim Hammerling
Why study algae?
•  Three distinct parts: a 'foot' that has the
nucleus, a stalk and a cap region.
•  Not microscopic, can grow to 5cm in length.
3
15-02-10
Joachim Hammerling
Alfred Hershey and Martha Chase
If he removed the cap, the cap grew back. If
he removed the foot, it did not.
Concluded the instructions for making the cap
were in the foot – possibly the nucleus.
He repeated his experiment and got the same
results.
Hershey and Chase
Hershey and Chase…
•  In 1952, they used radioactively labeled
bacteriophage (virus) to infect bacterial cells
•  Virus is made up of two parts: DNA and a
protein coat
•  DNA contains phosphorous but no sulfur.
•  Protein contains sulfur, but no phosphorus.
•  No one knew for certain
which became injected into
the host cell and was
involved in the creation of
new viruses.
•  Hershey and Chase radiolabelled viral
proteins with S-35 and viral DNA with P-32.
•  These radioisotopes are very unstable and
easy to measure the radioactive decay.
4
15-02-10
Hershey and Chase…
•  The viruses were allowed to infect the
bacterial hosts.
•  Only P-32 was present in the bacterial
cells - No S-35
Conclusion:
•  DNA, NOT protein, is the hereditary material
5