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Slide 3 of 37 Griffith and Transformation
Griffith and Transformation
In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria
caused pneumonia.
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Slide 4 of 37 Griffith and Transformation
Griffith made two observations:
(1) The disease-causing strain of bacteria grew into smooth colonies on culture plates.
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Slide 5 of 37 Griffith and Transformation
Griffith's Experiments
Griffith set up four individual
experiments.
Experiment 1: Mice were injected with the disease-causing
strain of bacteria. The mice developed
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Slide 6 of 37 Griffith and Transformation
Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick.
Harmless bacteria (rough colonies)
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Slide 7 of 37 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)
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Slide 8 of 37 Griffith and Transformation
Experiment 4: Griffith mixed his heat-killed, disease-causing
bacteria with live,
harmless bacteria and injected the mixture
into the mice. The mice developed pneumonia and died.
Live disease-causing bacteria (smooth colonies)
Dies of pneumonia
Heat-killed disease-causing bacteria (smooth colonies)
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Slide 9 of 37 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)
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Slide 10 of 37 Griffith and Transformation
Transformation
Griffith called this process transformation
because one strain of bacteria (the harmless strain) had changed permanently into another (the disease-causing strain).
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Slide 11 of 37 Avery and DNA
Avery and DNA
Oswald Avery repeated Griffith’s work to
determine which molecule was most important for transformation.
Avery and his colleagues made an extract from the heat-killed bacteria that they treated with
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Slide 12 of 37 Avery and DNA
The enzymes destroyed proteins, lipids,
carbohydrates, and other molecules, including the nucleic acid RNA.
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Slide 13 of 37 Avery and DNA
Avery and other scientists repeated the experiment using enzymes that would break down DNA.
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Slide 14 of 37 Avery and DNA
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Slide 15 of 37 Avery and DNA
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Slide 16 of 37 The Hershey-Chase Experiment
The Hershey-Chase Experiment
Alfred Hershey and Martha Chase studied
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Slide 17 of 37 The Hershey-Chase Experiment
Bacteriophages
A virus that infects bacteria is known as a
bacteriophage.
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Slide 18 of 37 The Hershey-Chase Experiment
When a bacteriophage enters a bacterium, the virus attaches to the surface of the cell and
injects its genetic information into it. The viral genes produce many new
bacteriophages, which eventually destroy the bacterium.
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Slide 19 of 37 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
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Slide 20 of 37 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 with
sulfur-35 in protein coat
Phage infects
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Slide 21 of 37 The Hershey-Chase Experiment
If 32P was found in the bacteria, then it was the DNA
that had been injected.
Bacteriophage with
phosphorus-32 in DNA
Phage infects
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Slide 22 of 37 The Hershey-Chase Experiment
Nearly all the radioactivity in the bacteria was from phosphorus (32P).
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Slide 23 of 37
The Components and Structure of DNA
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Slide 24 of 37 The Components and Structure of DNA
The Components and Structure of DNA
DNA is made up of nucleotides.
A nucleotide is a monomer of nucleic acids made up of a five-carbon sugar called
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Slide 25 of 37 The Components and Structure of DNA
There are four kinds of bases in in DNA:
•
adenine•
guanine•
cytosineCopyright Pearson Prentice Hall
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Slide 26 of 37 The Components and Structure of DNA
The backbone of a DNA chain is formed by sugar and phosphate groups of each nucleotide.
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Slide 27 of 37 The Components and Structure of DNA
Chargaff's Rules
Erwin Chargaff discovered that:
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The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA.Copyright Pearson Prentice Hall
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Slide 28 of 37 The Components and Structure of DNA
X-Ray Evidence
Rosalind Franklin used X-ray diffraction to get
information about the structure of DNA.
She aimed an X-ray beam at concentrated DNA
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Slide 29 of 37 The Components and Structure of DNA
The Double Helix
Using clues from Franklin’s pattern, James Watson and Francis Crick built a model that explained how DNA carried information and could be copied.
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Slide 30 of 37 The Components and Structure of
DNA
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Slide 31 of 37 The Components and Structure of
DNA
Watson and Crick discovered that hydrogen bonds can form only between certain base pairs—adenine and thymine, and guanine and cytosine.
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Slide 33 of 37 12–1
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.
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Slide 34 of 37 12–1
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.
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DNA is a long molecule made of monomers called
a. nucleotides. b. purines.
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Slide 36 of 37 12–1
Chargaff's rules state that the number of
guanine nucleotides must equal the number of a. cytosine nucleotides.
b. adenine nucleotides. c. thymine nucleotides.
Slide 37 of 37 12–1
In DNA, the following base pairs occur: a. A with C, and G with T.
