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12–1 DNA
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12–1 DNA
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Griffith and Transformation
Griffith and Transformation 1928
He isolated two different strains of pneumonia bacteria from mice and grew them in his lab.
Griffith made two observations:
(1) The disease-causing bacteria grew into smooth colonies on culture plates.
(2) The harmless strain grew into colonies with rough edges.
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12–1 DNA
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Griffith and Transformation
Griffith's Experiments
Experiment 1:
Mice were injected with the disease-causing strain of bacteria.
The mice developed pneumonia and died.
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Griffith and Transformation
Experiment 2:
Mice were injected with the harmless strain of bacteria.
These mice didn’t get sick.
Harmless bacteria (rough colonies)
Lives
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Griffith and Transformation
Experiment 3:
Griffith heated the disease-causing bacteria.
He then injected the heat-killed bacteria into the mice.
The mice survived.
Heat-killed disease-causing bacteria (smooth colonies)
Lives
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Griffith and Transformation
Experiment 4:
Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mice.
The mice developed pneumonia and died.
Live disease-causing bacteria(smooth colonies)
Dies of pneumonia
Heat-killed disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
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Griffith and Transformation
Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain.
Live disease-causing bacteria(smooth colonies)
Heat-killed disease-causing bacteria (smooth colonies)
Harmless bacteria (rough colonies)
Dies of pneumonia
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Griffith and Transformation
Transformation
Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones.
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Avery and DNA
Avery and DNA
Oswald Avery repeated Griffith’s work to determine which molecule caused the transformation.
When enzymes destroyed proteins, lipids or carbohydrates, transformation still occurred.
When DNA was destroyed, transformation did not occur. Therefore, they concluded that DNA was the transforming factor.
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The Hershey-Chase Experiment
The Hershey-Chase Experiment
Alfred Hershey and Martha Chase studied viruses that can infect living organisms.
A virus that infects bacteria is known as a bacteriophage.
Bacteriophages contain DNA or RNA and a protein coat.
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The Hershey-Chase Experiment
Bacteriophages
A bacteriophage injects its DNA into the bacteria.
The viral genes produce many new viruses which eventually destroy the bacterium.
When the cell splits open, hundreds of new viruses burst out.
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The Hershey-Chase Experiment
If Hershey and Chase could determine which part of the virus entered an infected cell, they would learn whether genes were made of protein or DNA.
They grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (35S).
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The Hershey-Chase Experiment
If 35S was found in the bacteria, it would mean that the viruses’ protein had been injected into the bacteria.
Bacteriophage withsuffur-35 in protein coat
Phage infects bacterium
No radioactivity inside bacterium
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The Hershey-Chase Experiment
If 32P was found in the bacteria, then it was the DNA that had been injected.
Bacteriophage withphosphorus-32 in DNA
Phage infects bacterium
Radioactivity inside bacterium
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The Hershey-Chase Experiment
Nearly all the radioactivity in the bacteria was from phosphorus (32P).
Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.
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The Components and Structure of DNA
The Components and Structure of DNA
DNA is made up of nucleotides:
- five-carbon sugar called deoxyribose,
- phosphate group,
- nitrogenous base.
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The Components and Structure of DNA
There are four kinds of bases in in DNA:
• adenine
• guanine
• cytosine
• thymine
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The Components and Structure of DNA
The sides (backbone) of DNA are alternating sugars & phosphate groups.
The rungs of the ladder are the base pairs.
• Guanine [G] and cytosine [C] bases are equal.
• Adenine [A] and thymine [T] bases are equal.
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The Components and Structure of DNA
The Double Helix
Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other.
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The Components and Structure of DNA
DNA Double Helix
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Avery and other scientists discovered that
a. DNA is found in a protein coat.
b. DNA stores and transmits genetic information from one generation to the next.
c. transformation does not affect bacteria.
d. proteins transmit genetic information from one generation to the next.
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The Hershey-Chase experiment was based on the fact that
a. DNA has both sulfur and phosphorus in its structure.
b. protein has both sulfur and phosphorus in its structure.
c. both DNA and protein have no phosphorus or sulfur in their structure.
d. DNA has only phosphorus, while protein has only sulfur in its structure.
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DNA is a long molecule made of monomers called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.
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Chargaff's rules state that the number of guanine nucleotides must equal the number of
a. cytosine nucleotides.
b. adenine nucleotides.
c. thymine nucleotides.
d. thymine plus adenine nucleotides.
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In DNA, the following base pairs occur:
a. A with C, and G with T.
b. A with T, and C with G.
c. A with G, and C with T.
d. A with T, and C with T.