Transcript 8.1 Identifying DNA as the Genetic Material

8.2
of DNA
•SetStructure
up Cornell Notes
on
pg. 3
•Topic: 8.1 Identifying
DNA as the Genetic
Material
•Essential Question:
Summarize: Why was
bacteriophage an
excellent choice for
research to determine
whether genes are made
of DNA or proteins?
8.1Atoms,
Identifying
2.1
Ions, DNA as the Genetic
and Molecules Material
Summarize: Why was bacteriophage an
excellent choice for research to determine
whether genes are made of DNA or
proteins?
Key Concept:DNA was
identified as the genetic
material through a series of
experiments
8.1 Identifying DNA as the Genetic Material
KEY CONCEPT
DNA was identified as the genetic material through a
series of experiments.
8.1 Identifying DNA as the Genetic Material
• Frederick Griffith (1928)
– Microbiologist studying the bacterium that causes
pneumonia to create a vaccine
» He studied two types
o S- smooth- Pneumonia + death
o R- rough- Pneumonia + recovery
8.1 Identifying DNA as the Genetic Material
Hypothesize what would Griffith expect to find if he
combined the live S bacteria with live R bacteria?
+
8.1 Identifying DNA as the Genetic Material
Griffith’s Experiments
• Griffith injected the two types of bacteria into mice
• What should Griffith expect to find when he injects the S
(encapsulated) bacteria into the mice?
• What about the R (non-encapsulated) bacteria?
8.1 Identifying DNA as the Genetic Material
• Hypothesize why only the S
(encapsulated) strain would
be deadly.
• The capsule protects the
bacteria from the immune
system!
8.1 Identifying DNA as the Genetic Material
•Hypothesize what happened when Griffith heat-killed the S
bacteria and injected it into the mice.
•When Griffith heat-killed the S bacteria and injected it into the
mice, they were unaffected (healthy and alive).
8.1 Identifying DNA as the Genetic Material
Hypothesize what Griffith expect to find if he combined the
dead S bacteria with live R bacteria?
8.1 Identifying DNA as the Genetic Material
•When Griffith injected mice with a combination of heatkilled S bacteria and R bacteria the mouse died!!!
What do you think he found when he took a blood test of the
dead mouse?
8.1 Identifying DNA as the Genetic Material
•When he did a blood test on the dead mouse he found live S bacteria
in the dead mice!
8.1 Identifying DNA as the Genetic Material
Table Talk
Hypothesize with your table about what happened when
the heat-killed S bacteria was combined with the R
bacteria.
Remember:
– Live R= live mouse
– Heat-killed S= live mouse
– Live R + Heat-killed S= dead mouse
8.1 Identifying DNA as the Genetic Material
• A “transforming material” passed from dead S bacteria to
live R bacteria, making them deadly.
8.1 Identifying DNA as the Genetic Material
• Oswald Avery, a biologist, spent 10 years trying to
figure out what Griffith had discovered (1944)
• He combined R bacteria with an extract made from S
bacteria and observed R bacteria turning into S
bacteria.
8.1 Identifying DNA as the Genetic Material
• Wanted to know if it was DNA or protein that
transformed harmless R bacteria into deadly S bacteria
– tests showed DNA was
present when proteins
were not.
– chemical makeup
matched that of DNA.
8.1 Identifying DNA as the Genetic Material
Avery’s Experiments (DEMO)
• Broke down the Heat-killed S bacteria into its
components
– Carbohydrates
– Lipids
– Proteins
– DNA
– RNA
• He then added Live R bacteria
• What should we expect to happen to each animal?
• Rabbit 1: Carbs
• T-Rex 2: Lipids
• Rabbit 3: Proteins
• Snail 4: DNA
• Elephant 5: RNA
8.1 Identifying DNA as the Genetic Material
Avery’s Experiments Cont’ (DEMO #2)
Even though this was good evidence that DNA was the
genetic material, more evidence was needed.
• This time scientists decided to add enzymes that
destroyed specific components of the Heat-killed S
bacteria
• What should we expect to happen to each animal?
• Rabbit 1: Carb destroying enzyme
• T-Rex 2: Lipid destroying enzyme
• Rabbit 3: Protein destroying enzyme
• Snail 4: DNA destroying enzyme
• Elephant 5: RNA destroying enzyme
8.1 Identifying DNA as the Genetic Material
– Transformation ONLY stopped when an
enzyme was added that destroyed DNA!!!
8.1 Identifying DNA as the Genetic Material
• He thought DNA was the transforming principle, but more
proof was needed…
8.1 Identifying DNA as the Genetic Material
• Hershey and Chase studied viruses that infect bacteria, or
bacteriophages. (1952)
8.1 Identifying DNA as the Genetic Material
–They tagged viral
proteins with radioactive
sulfur
• They tagged viral DNA
with radioactive
phosphorus
• Tagged DNA was found inside the bacteria; tagged
proteins were not.
• This confirmed that DNA was the genetic
material!
8.1 Identifying DNA as the Genetic Material
8.1 Identifying DNA as the Genetic Material
Biologix DNA Video