12.1 Flashcards
He isolated two strains of the same bacterial species from
mice, and then he grew them ……. but only
one caused pneumonia.
In culture plates
The disease-causing bacteria
(S strain) grew into smooth
colonies,
the harmless bacteria
(R strain) produced
rough edge colonies.
He injected mice with the disease-causing bacteria (S
strain), they developed
pneumonia and died.
Then he injected mice with the harmless bacteria(R strain), they
they stayed healthy.
Griffith took a culture of the S strain heated the cells to kill
them, then injected the heat-killed bacteria into laboratory
mice.
The mice survived, suggesting that the cause of
pneumonia was not a toxin from the disease-causing
bacteria.
In his next experiment he mixed
heat-killed S strain bacteria + live R strain harmless bacteria
He injected this mixture into the mice, the injected mice
developed pneumonia and died.
In the second experiment what happened when he examined the lungs of the mice?
When he examined the lungs of these mice, he found
them to be filled with the disease-causing bacteria.
The heat-killed bacteria somehow passed their disease-
causing ability to the harmless bacteria.
What did he reason at the end of his second experiment?
He reasoned that when he mixed them together some
chemical factor was transferred from the heat-killed S
strain to the live R strain.
What did he call this process?
He called this process transformation, because one type
of bacteria had been changed permanently into another.
What did Griffith conclude?
Griffith concluded that the transforming factor was a gene.
What is the transforming factor
There was just one possible explanation that DNA was the
transforming factor.
Bacteriophage
Bacteriophage: a kind of virus that infects bacteria
What did Hershey and chase study? And why?
Hershey and chase studied a bacteriophage that was
composed of a DNA core and a protein coat.
They wanted to determine which part of the virus entered
the bacteria
What are the viruses Hershey and chase grow?
They grew viruses in cultures containing radioactive
isotopes of phosphorous-32 and sulfur-35.
Proteins contain ….., and DNA contain ….
Proteins contain sulfur, and DNA contain phosphorous.
If they found radioactive from sulfur in the bacteria, it
means
it
means the protein coat entered the bacteria,
if they
found radioactive phosphorous
and it means DNA has been
injected.
They found out that all the radioactivity in the bacteria
was
from phosphorous.
Hershey and Chase concluded that the genetic material of
the bacteriophage
was DNA not protein.
The Role of DNA: Summary
DNA stores information needed by every living cell, its role:
1
Store information
2. Copy information for daughter cells
3. Transmit information to daughter cells
