Download DNA: Information Molecule

DNA: Information Molecule
How did scientists use evidence to
discover that the DNA molecule
contains information for an organism’s
characteristics (traits)?
Objectives
• Explain with evidence that DNA is the
information carrying molecule of
organisms
– Griffith and Avery
– T2 virus
• Describe one way DNA can be transferred
laterally between organisms.
– Bacterial transformation
– Viral transduction
Can molecules act as information
to determine an organism’s traits?
Can molecules from one strain
of bacteria cause a different
strain of bacteria to have
similar traits?
Words to know
• Benign – not harmful
– pronounce buh-nine
– Root word: good (Think “bien”)
– A benign tumor is not dangerous.
• Virulent – harmful (active) bacteria
– Pronounce veer-you-lent
– Root word: virus
Figure 11.1a
There are two strains of Streptococcus pneumoniae.
ROUGH COLONY (R)
R strain is benign
(Lacking a protective
capsule, it is recognized
and destroyed by
host’s immune system)
SMOOTH COLONY (S)
S strain is virulent
(Protective capsule
prevents detection by
host’s immune system)
Narrated animation of experiment
Griffith’s experiments
http://nortonbooks.com/college/biology/animations/ch12a01.htm
Figure 11.1b
Explain each treatment: What is
purpose for each control?
What data shows the heat-killed
S strain did not cause death of
the mouse in treatment #4?
What data shows S strain
molecules cannot kill the mouse
alone; the streptococcus must be
alive?
What data shows that the R
strain alone will not kill the
mouse?
What data shows that the S
strain IS virulent?
Mechanism
Bacteria can take in pieces of DNA from
their environment.
This process is called transformation
because in Griffith’s experiment the R
strain was transformed into an S strain by
taking in DNA from the dead molecules.
Griffith’s Conclusion
• The R strain was able to take in molecules from
the dead S strain.
• These molecules somehow gave the R strain
characteristics of the dead S strain.
– Ability to make protective coating
So, we know that there is a molecule that transfers
information…
BUT…we still haven’t proved what those
molecules are!
Which molecules could be responsible
for the information in cells?
Type of molecule
Lipids (fats)
Proteins
DNA
RNA
Made of
Example
Experiment to determine which molecule
in cells acts as information for traits
1. Take material from dead virulent (S-strain)
Streptococcus. Remove lipid & carbohydrate.
2. Separate remaining molecules into three test
tubes.
3. Treat each with a different enzyme to destroy
one type of molecule.
A. One test tube has DNA and RNA, but NO PROTEIN
B. One test tube has DNA and protein, but NO RNA
C. One test tube has RNA and protein, but NO DNA
Figure 11.2
DETERMINING THAT DNA IS THE HEREDITARY MATERIAL
Heat-killed
S cells
1. Remove the lipids
and carbohydrates
from a solution of
heat-killed S cells.
Proteins, RNA, and
DNA remain.
Lipids
Carbohydrates
Add
proteinases
Sample should
Contain
NO PROTEIN
Add
ribonuclease
Sample should
Contain
NO RNA
Add
deoxyribonuclease
2. Subject the
solution to
treatments of
Sample should enzymes to destroy
Contain
either the proteins,
NO DNA
RNA, or DNA.
3. Add a small
portion of each
sample to a culture
containing R cells.
Observe whether
transformation has
occurred by testing
for the presence
virulent S cells.
PREDICTIONS
Hypotheses
DNA is the
information
molecule
RNA is the
information
molecule
Protein is the
information
molecule
no protein in
sample
no RNA in
sample
no DNA in
sample
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Will the sample make
R cells become S?
Figure 11.2
DETERMINING THAT DNA IS THE HEREDITARY MATERIAL
Heat-killed
S cells
1. Remove the lipids
and carbohydrates
from a solution of
heat-killed S cells.
Proteins, RNA, and
DNA remain.
Lipids
Carbohydrates
Add
proteinases
Sample should
contain
NO PROTEIN
Add R cells
S cells
appear
Transformation occurs
Add
ribonuclease
Sample should
contain
NO RNA
Add
deoxyribonuclease
Sample should
contain
NO DNA
2. Subject the
solution to
treatments of
enzymes to destroy
either the proteins,
RNA, or DNA.
3. Add a small
portion of each
sample to a culture
containing R cells.
S cells
No S cells Observe whether
appear
appear
transformation has
occurred by testing
No transformation occurs
for the presence
virulent S cells.
Add R cells
Add R cells
RESULT
no protein in
sample
S Cells become
R cells
no RNA in
sample
S Cells become
R cells
no DNA in
sample
S Cells DO NOT
become R cells
Conclusion:
Transformation cannot occur unless DNA is
present. Therefore DNA is likely the
hereditary material.
Is the hereditary information
composed of DNA or Protein?
T2 Virus
Bacterial
Cell
Figure 11.3
DNA or
protein?
DNA or
protein?
1. Viruses are made of
DNA and proteins. To
reproduce, the virus injects
it’s hereditary information
into the host cell.
2. Is the protein or
the DNA injected?
3. Do proteins or DNA
carry the hereditary
information for the
viruses to replicate?
Narrated animation of experiment
Bacteriophage experiments
http://trc.ucdavis.edu/biosci10v/bis10v/media/ch09/bacteriophage_studies.html
PREDICTIONS based on the two
different hypotheses
Hypotheses
Viruses with
radioactive proteins
infect bacteria
Viruses with
radioactive DNA
infect bacteria
DNA is injected by
Where will radioactivity be
the virus as the
found?
information molecule [inside] or [outside] the cells
Where will radioactivity be
found?
[inside] or [outside] the cells
PROTEIN is injected Where will radioactivity be
by the virus as the
found?
information molecule [inside] or [outside] the cells
Where will radioactivity be
found?
[inside] or [outside] the cells
RESULTS
Viruses with
radioactive proteins
infect bacteria
Viruses with
radioactive DNA
infect bacteria
Radioactivity is found only
Radioactivity is found only
OUTSIDE the bacteria
INSIDE the bacteria
Results:
Because the reproduced cells showed
radioactivity on the inside when the DNA
was injected, but not the protein, we can
conclude that DNA is the molecule that
acts as information for traits.
Figure 11.3
Virus protein coat
m
Host cell
embrane
Virus DNA
1. Start of infection.
Virus DNA enters host
cells. Protein coat
does not.
2. Virus DNA directs
the production of new
virus particles.
3. End of infection.
New generation of
virus particles burst
from host cell.
What we learned
9DNA is the molecule that carries information
9Information in DNA determines which
proteins can be made by an organism
9DNA can be passed between organisms in
nature by viruses
9Bacteria can take in pieces of DNA from
their environment. This process is called
transformation.
How we use this understanding
• We can manipulate DNA in the laboratory and
add it to organisms.
• Because DNA carries information for an
organism’s characteristics, we can give new
characteristics to organisms
• In our lab we will change the characteristics of
an organism through bacterial transformation
• We will study the ethics and implications of this
technology- genetically modified organisms
(GMO’s) and GM foods.