Download DNA Replication

DNA
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DNA
 Deoxyribonucleic acid
found in the nucleus of
every cell
 DNA and proteins make
up chromosomes – contain
traits
 sections of it make up
genes
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DNA
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History
of DNA
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History of DNA
• Early scientists thought
protein was the cell’s
hereditary material
because it was more
complex than DNA
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Transformation
• Fred Griffith worked with
harmful Smooth (S) and harmless
Rough (R) strain Pneumoccocus
bacteria - pneumonia
• He found that R strain could
become harmful when it took in
DNA from heat-killed S strain
• Study suggested that DNA was
probably the genetic material
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Griffith’s Experiment
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History of DNA
Oswald Avery 1944
performed Griffith’s
experiment but added
enzymes to kill proteins,
lipids, carbs, and RNA
and transformation still
occurred
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History of DNA
Oswald Avery 1944
 added enzymes to kill
DNA and transformation
didn’t occur
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History of DNA
Oswald Avery 1944
 proved DNA makes up
genes and chromosomes
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History of DNA
Alfred Hershey and Martha Chase1952
Conducted a series of
experiments with
bacteriophages – virus that
infects bacteria- which
identified DNA, not
protein, to be the genetic
material of cells.
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• The Hershey-Chase Experiment
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Mix radioactively
labeled phages with
bacteria. The phages
infect the bacterial
cells.
Phage
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Agitate in a blender
to separate phages
outside the bacteria
from the cells and
their contents.
Radioactive
protein
Bacterium
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Centrifuge the mixture
so bacteria form a
pellet at the bottom of
the test tube.
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Empty
protein shell
Measure the
radioactivity in
the pellet and
liquid.
Radioactivity
in liquid
Phage
DNA
DNA
Batch 1
Radioactive
protein
Centrifuge
Pellet
Batch 2
Radioactive
DNA
Figure 10.1B
Radioactive
DNA
Centrifuge
Pellet
Radioactivity
in pellet
Erwin Chargaff
• Discovered two important
rules to the structure of
DNA
• Showed that the number of
G = C and A = T
• Showed that DNA
composition varies between
species
• Known as Chargaff’s Rules
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DNA Structure
• Rosalind Franklin 1951
• took x-ray diffraction
photographs of DNA
• X-ray diffraction reveals
the shape of a molecule
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Rosalind Franklin
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History of DNA
James Watson and Francis Crick
1953
Used Franklin’s xrays to discover the
structure of DNA
 called structure
the double helix
Won Nobel Prize in
1962
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History of DNA
Alfred Hershey and Martha
Chase 1952
 In the first experiment, phages with
radioactive 32P-labeled DNA infected
bacteria. In a second experiment, phages
with radioactive 35S-labeled protein infected
bacteria. In the first experiment, most
radioactivity was found in the infected
bacteria, while in the second experiment most
radioactivity was found in the phage coat.
These experiments demonstrated that DNA is
the genetic material of phage and that
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protein does not transmit genetic information.