Download Introduction to DNA (Deoxyribonucleic acid)

Introduction to DNA (Deoxyribonucleic acid)
Questions at the beginning of the 20th Century
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How do genes work?
What are they made of, and how do they determine the characteristics of organisms?
Are genes single molecules, or are they longer structures made up of many molecules?
How did we figure out the answers to these questions?
The discovery of the gene and DNA:
Griffith Transformation Experiment:
Like many experiments in science, the discovery of the molecular nature of the gene was a complete
accident. In 1928, British scientist Fredrick Griffith was trying to figure out how bacteria made
people sick.
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Griffith isolated two slightly different strains of _____________________________ from mice.
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One strain that ______________ pneumonia and one strain that ________________cause
pneumonia.
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The pneumonia causing strain grew on nutrient agar plates in ________________colonies.
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The non-pneumonia causing bacteria grew on nutrient agar plates as colonies with
_______________ edges.
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This is how Griffith distinguished the two types of bacteria.
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When Griffith injected mice with the ________________________ strain of bacteria, the mice
developed pneumonia and
____________.
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When mice were injected with the
______________ strain, the mice
didn’t get sick.
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Griffith wondered if the diseasecausing bacteria might produce
________________.
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To find out, Griffith took a
____________ of these cells, heated
the bacteria to kill them, and injected
the heat-killed bacteria into the mice.
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The mice __________________!
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This suggested that the cause of pneumonia was not a _____________________ released by the
bacteria.
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Next, Griffith _____________ heat-killed, disease-causing bacteria with live harmless bacteria
and injected the mixture into mice.
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By themselves, _________________ should have made the mice sick
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To Griffith’s amazement, the mice __________________________________________________.
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When Griffith examined the lungs of the mice, he found that the lungs were _______________
with the ________________________________________.
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Somehow the heat killed strain of bacteria had _________________ their disease causing ability
to the ____________________________________.
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Griffith called this process ____________________ because one strain of bacteria (the harmless
strain) had apparently been changed permanently into another (the disease-causing strain).
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Griffith hypothesized that when the living, ____________________ and the
____________________ bacteria were mixed; some _____________ was transferred from the
heat-killed cells into the live cells.
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Those factors must ____________ ______________ that could change harmless bacteria into
disease-causing bacteria.
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Since the ability to cause disease was _______________ by the transformed bacteria’s offspring,
the transformation factor might be a ______________.
AVERY and DNA
In 1944, a group of scientists led by
Oswald Avery tried to repeat Griffith’s
work. They did so to determine which
molecule in the heat-killed bacteria was
most important in transformation. If
transformation required just one
particular molecule, that might be the
molecule of the gene.
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Avery and his colleagues
_______________ all the “juice” from
the inside of the heat-killed bacteria.
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They treated the extract with
_____________that destroy proteins,
lipids, carbohydrates, and other
molecules including the nucleic acid
that makes up RNA.
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_________________________ still occurred.
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Since all of the molecules listed above had been _________________, they could not be
responsible for ________________________.
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Avery and other scientists performed another experiment, this time using an _______________
that destroyed the nucleic acid that makes up _________.
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This time, ____________________ did not occur.
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This lead to Avery coming to the conclusion that _______ was_________________ factor.
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Avery and other scientist discovered that the _____________________________ stores and
transmits the _____________ information from one generation of an organism to the next.
Hershey-Chase Experiment
In 1952, Alfred Hershey and Martha Chase studied viruses to further
convince the scientist that genetic information is passed along from
generation to generation by DNA.
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They collaborated in studying viruses,
________________________________________________________
________________________________________________.
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Bacteriophages:
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Composed of _____ or RNA core and a ____________ coat.
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When a bacteriophage enters a bacterium, the virus attaches to the surface of the cell
and injects its ______________________ inside the bacteria.
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The ______________ genes are
inserted into the host DNA and tell the
bacteria cell to produce hundreds of
viruses.
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Gradually the viruses ____________
the _________________causing the
cell to split open releasing the viruses.
Hershey and Chase reasoned that if they
could determine which part of the virus, the
_________________________ or the
_________ core, entered the infected cell,
they would learn whether genes were made
of protein or DNA.
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To do this, they grew viruses in cultures containing _________________________________.
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________________ contains very little phosphorus and __________ contains no sulfur.
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These radioactive substances could be used as ___________________.
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If ________________________ was found in the bacteria, the virus would have injected
its protein coat into the bacterium.
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If ________________________ was found in the bacterium, the virus would have
injected its DNA into the bacterium.
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The two scientists mixed the marked viruses with the bacterium and then waited a few minutes
so the viruses had time to inject their genetic material.
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They separated the viruses from the bacteria and tested the bacteria for ___________________.
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Nearly all of the radioactivity found in the bacteria was from __________________________.
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Hershey and Chase concluded that the genetic material of the bacteriophage was________, not
____________________.