8.2 Structure of DNA Set up Cornell Notes on pg. 91 Topic: 8.1 Identifying DNA as the Genetic...

8.2 Structure of DNA•Set up Cornell Notes on pg. 91

•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?

2.1 Atoms, Ions, and Molecules

Summarize: Why was bacteriophage an excellent choice for research to determine whether genes are made of DNA or proteins?

8.1 Identifying DNA as the Genetic Material

Key Concept:DNA was identified as the genetic material through a series of experiments

8.2 Structure of DNA

• Pg 90Summarize: Avery Demo #1

Summarize: Avery Demo #2


KEY CONCEPT DNA was identified as the genetic material through a series of experiments.


Pneumonia • Pneumonia is an infection in one or both of

your lungs.• Can be caused by bacteria/viruses• OUR FOCUS: Streptococcus pneumoniae

(bacteria)• When the germs that cause pneumonia

reach your lungs, the lungs' air sacs (alveoli) become inflamed and fill up with fluid. This causes the symptoms of pneumonia, such as a cough, fever, chills, and trouble breathing.

• When you have pneumonia, oxygen may have trouble reaching your blood. If there is too little oxygen in your blood, your body cells can't work properly. Because of this and the infection spreading through the body, pneumonia can cause death.


Pneumonia was a serious cause of death in the wake of the post-WWI Spanish influenza pandemic

Frederick Griffith (1928) Microbiologist studying the bacterium that causes pneumonia to create a vaccine–He studied two types:

• S strain (smooth): which was virulent and encapsulated in a coat of sugar molecules

• R strain (rough): was not virulent and was non-encapsulated


• Griffith injected the two types of bacteria into mice

• Hypothesize what should Griffith expect to find when he injects the S (encapsulated) bacteria into the mice?

• What about the R (non-encapsulated) bacteria?

Griffith’s Experiments

Unaffected


• Hypothesize why only the S (encapsulated) strain would be deadly.

• The capsule protects the bacteria from the immune system!


Hypothesize what would Griffith expect to find if he combined the live S bacteria with live R bacteria?

+Live S + Live R=Rationale:


•Hypothesize what happened when Griffith heat-killed the S bacteria and injected it into the mice.

Heat-killed S=Rationale:

Unaffected


Hypothesize what Griffith expect to find if he combined the dead S bacteria with live R bacteria?

Heat-killed S + Live R=Rationale:


•When Griffith injected mice with a combination of heat-killed S bacteria and R bacteria the mouse died!!!

What do you think he found when he took a blood test of the dead mouse?


•When he did a blood test on the dead mouse he found live S bacteria in the dead mice!


Table Talk

Remember:–Live R= unaffected live mouse

–Heat-killed S= unaffected live mouse

–Live R + Heat-killed S= dead mouse

Hypothesize with your table about what happened when the heat-killed S bacteria was combined with the R bacteria.


• Griffith hypothesized that a “transforming material” passed from dead S bacteria to live R bacteria, making them turn into deadly S bacteria.

• “Transformation” suggested that bacteria are capable of transferring genetic material from one bacteria to another


• 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 under a microscope.


• He 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 makeupmatched that of DNA.


Avery’s Experiments (DEMO): TOP P. 90

• Broke down the Heat-killed S bacteria into its components– DNA– Lipids– Carbohydrates– Proteins– RNA

carbohydrates

Lipids

Proteins

DNA

RNA



• He then added Live R bacteria (dead S + Live R)• What should we expect to happen to each animal?

• Pig: Carbs=

• T-Rex : Lipids=

• Owl: Proteins=

• Snail : DNA=

• Elephant : RNA=



What should we expect to happen to each animal?

• Pig: Carbs--------------- LIVE!!!!

• T-Rex 2: Lipids--------- LIVE!!!!

• Owl: Proteins----------- LIVE!!!!

• Snail 4: DNA------------ DEAD!!!!

• Elephant 5: RNA------- LIVE!!!!



Summarize how Avery’s first experiment supports the theory that DNA is the “transforming principle”.


carbohydrates

Lipids

Proteins

DNA

RNA

Avery’s Experiments Cont’ (DEMO #2) Bottom: P. 90

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


carbohydrates

Lipids

Proteins

DNA

RNA


This time scientists decided to add enzymes that destroyed specific components of the Heat-killed S bacteria

• DNA destroying enzyme


carbohydrates

Lipids

Proteins

DNA

RNA



• Lipid destroying enzyme


carbohydrates

Lipids

Proteins

DNA

RNA



• Carbohydrate destroying enzyme


carbohydrates

Lipids

Proteins

DNA

RNA



• Protein destroying enzyme


carbohydrates

Lipids

Proteins

DNA

RNA



• RNA destroying enzyme




• Pig: Carb destroying enzyme=

• T-Rex : Lipid destroying enzyme=

• Owl: Protein destroying enzyme=

• Snail : DNA destroying enzyme=

• Elephant: RNA destroying enzyme=


Avery’s Experiments (DEMO): Bottom P. 90


• Pig: Carbs--------------- DEAD!!!!

• T-Rex 2: Lipids--------- DEAD!!!!

• Owl: Proteins----------- DEAD!!!!

• Snail 4: DNA------------ LIVE!!!!

• Elephant 5: RNA------- DEAD!!!!


Avery’s Experiments (DEMO): Bottom P. 90

Summarize how Avery’s second experiment supports the theory that DNA is the “transforming principle”.


– Transformation ONLY stopped when an enzyme was added that destroyed DNA!!!


• He thought DNA was the transforming principle, but more proof was needed…


• Hershey and Chase studied viruses that infect bacteria, or bacteriophages. (1952)


• They tagged viral proteins with radioactive sulfur

• Sulfur is found in protein, but NOT in DNA

• They tagged viral DNA DNA with radioactive phosphorus

• Phosphorus is found in DNA, but NOT in protein

bacterium bacterium


bacterium bacterium

• When they examined the bacteria, they found no significant radioactivity

• This time radioactivity was clearly present in the bacteria!


• Tagged DNA was found inside the bacteria; tagged proteins were not.

• This confirmed that DNA was the genetic material!


Biologix DNA Video (28m46s)

• Answer ALL questions

8.2 Structure of DNA Set up Cornell Notes on pg. 91 Topic: 8.1 Identifying DNA as the Genetic...

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