Transcript 12.1 DNA as Genetic Factor File

Ch.12-1
Identifying the Substance of Genes
POINT > Describe Griffith’s experiments
with bacteria and mice
POINT > Describe Avery’s experiments that
identified DNA as genetic material
POINT > Describe Hershey & Chase
experiments with viruses
Griffith’s Bacterial Transformations
Avery’s Continuation of Griffith’s Work
Hershey & Chase’s Viral Isotopes
POINT > Describe Griffith’s
experiments with bacteria and
mice
British scientist researching
bacteria
Griffith studied how bacteria
cause pneumonia
POINT > Describe Griffith’s experiments with
bacteria and mice
He used two similar bacterial types
S-strain: Looked smooth due to
outer coating of saccharide
molecules. Causes disease (virulent)
R-strain: Looked rough – no
saccharide coating. Harmless
POINT > Describe Griffith’s experiments
with bacteria and mice
1. Injected each strain into mice
S:Virulent…
R: Harmless…
POINT > Describe Griffith’s experiments
with bacteria and mice
Griffith then heat-killed S-strain bacteria &
injected into mice
Harmless…
POINT > Describe Griffith’s experiments
with bacteria and mice
He then mixed living R-strain with heatkilled S-strain bacteria
Virulent…
POINT > Describe Griffith’s experiments
with bacteria and mice
Conclusions from the experiment:
1. Some “factor” was transferred from heat-killed
S-strain to living R-strain
2. “Factor” must contain information causing a
transformation: able to change harmless bacteria into
disease-causing bacteria
3. “Factor” must be a gene, because disease-causing
ability was inherited by offspring bacteria
WB CHECK:
Griffith discovered that
a) DNA is the genetic material
b) some factor from virulent bacteria could cause
disease even if the bacteria was killed
c) some factor from virulent bacteria could cause
harmless bacteria to become virulent
d) harmless bacteria could become virulent if
exposed to heat
POINT > Describe Avery’s
experiments that identified DNA
as genetic material
Canadian biologist, used
Griffith’s results as starting
point
Which molecule in the heat-killed bacteria
was the key for transformation?
POINT > Describe Avery’s experiments that
identified DNA as genetic material
1.
Heat-killed S-strain, making it harmless,
and extracted the macromolecules:
proteins, carbohydrates, RNA, DNA
POINT > Describe Avery’s experiments that
identified DNA as genetic material
2.
Treated the extract with an enzyme that
destroys proteins. Then repeated with
enzymes to destroy lipids, carbs, RNA
Protease
(destroys protein)
POINT > Describe Avery’s experiments that
identified DNA as genetic material
He added treated extracts to harmless R-strain
They became
virulent!
Protease
(destroys protein)
+
POINT > Describe Avery’s experiments that
identified DNA as genetic material
4.
Avery repeated the experiment using an
enzyme that destroys DNA
DNase
(destroys DNA)
Harmless!
+
POINT > Describe Avery’s experiments that
identified DNA as genetic material
Avery’s conclusions:
1. DNA was the transforming factor
2. DNA stored & transmitted the information
for causing disease
WB CHECK:
Avery showed that
a) enzymes that destroy protein destroy the genetic
material
b) enzymes that destroy DNA destroy the genetic
material
c) carbohydrates are important in heredity
d) DNA had to be the genetic material
e) all of the above
f) a and d
g) b and d
POINT > Describe Hershey &
Chase experiments with viruses
American scientists
Experiments with viruses provided more
evidence to support Avery’s work
POINT > Describe Hershey & Chase
experiments with viruses
Hershey/Chase used bacteriophage:Virus that
infects bacteria by attaching to surface and
injecting its genetic information
POINT > Describe Hershey & Chase
experiments with viruses
Hershey/Chase used bacteriophage:Virus
that infects bacteria by attaching to surface
and injecting its genetic information
Structure of a bacteriophage:
POINT > Describe Hershey & Chase
experiments with viruses
Radioactive elements can be used to trace molecules
1. Phages grown in different conditions (based on
elements of macromolecules)
DNA has lots of phosphorus, no sulfur
Grown in radioactive phosphorus-32 (32P)
Protein has lots of sulfur, no phosphorus
Grown in radioactive sulfur-35 (35S)

POINT > Describe Hershey & Chase
experiments with viruses
2. S-35-labelled phages were added to bacteria
and allowed to reproduce
POINT > Describe Hershey & Chase
experiments with viruses
3. Phages & bacteria were separated & analyzed
to detect location of radioactivity
Bacteria were not radioactive
POINT > Describe Hershey & Chase
experiments with viruses
4. Repeated experiment with P-32 phages &
analyzed to detect location of radioactivity
Bacteria were radioactive!
POINT > Describe Hershey & Chase
experiments with viruses
Conclusion:
DNA was genetic material found in genes of
other organisms (confirming and adding to
Avery’s results)
WB CHECK:
Hershey & Chase showed that
a) bacteriophages are made of protein and DNA
b) radioactive sulfur showed up in infected bacteria
c) radioactive phosphorus showed up in infected
bacteria
d) DNA had to be the genetic material
e) all of the above
f) c and d
g) a and d
If genes are made of DNA, DNA must be able
to:
1. Store information
2. Replicate (during S-phase)
3. Transmit information (via sexual & asexual
reproduction)
We know DNA is a macromolecule of nucleic
acid
…we know its importance as the genetic
material…
…we know that it stores and transmits genetic
information…
…so what is the structure of DNA, that allows it
to do these things?
Homework:
Read pages 338-343!!
Assess #1-3 page 343
Workbook page 202