Transcript Chapter 12 DNA and RNA - Lincoln Park High School

Chapter 12
DNA and RNA
12-1 DNA
1. Griffith and
Transformation
Explain DNA’s role in your
existence.
Discuss
with your partner.
1. Griffith & Transformation
In
the 1920’s Griffith was a biologist
trying to figure out how bacteria
produced pneumonia (a deadly
disease).
2
different stains (breeds) of
pneumonia bacteria were isolated
(separated) from mice
 He grew the pneumonia in the lab
Griffith made two
observations:
(1)
The disease-causing strain
of bacteria grew into smooth
colonies on culture plates.
(2) The harmless strain grew
into colonies with rough
edges.
Griffith’s Experiments
 Griffith
set up four
individual
experiments.
 Experiment 1:
Mice were
injected with the
disease-causing
strain of bacteria.
The mice
developed
pneumonia and
died.
Experiment
2:
Mice were
injected with
the harmless
strain of
bacteria.
These mice
didn’t get sick
Experiment
3:
Griffith heated
the diseasecausing
bacteria. He
then injected
the heat-killed
bacteria into
the mice. The
mice survived
 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.
Conclusion:
the
heat-killed
bacteria
passed their
disease-causing
ability to the
harmless strain
TRANSFORMATION
One
strain of bacteria is
changed by a gene or genes
from another strain of bacteria.
What
was Griffith trying to learn
when he set up this
experiment? Discuss w/ your
partner.
 Griffith
hypothesized that something
must have information that could
change harmless bacteria into
disease-causing ones
Discuss:
Who
remembers getting
immunizations ? Why do
people get immunizations?
How do they work?
Ethical Question:
Some
people believe autism is
caused by preservatives in the
vaccine. As a result some
people have chosen not to
immunize their children. What is
your opinion?
2. Avery and DNA
In
the 1940’s a scientist named
Avery repeated Griffith’s
experiment
The research question: what
molecule in the heat-killed
bacteria was the most important
part of transformation. That
molecule is probably a part of
the gene that allows
transformation to take place.
The Experiment
 Avery
& other
scientists made a
bacterial extract
(juice) from the
heat-killed
bacteria and
destroyed all of
the molecules w/
enzymes
The
enzymes destroyed
 Proteins
 Lipids
 Carbohydrates

RNA
transformation still occurred,
therefore those molecules are
not responsible for
transformation

The
experiment was repeated using
enzymes that destroy DNA.
Transformation did not occur
They concluded that DNA stores &
transmits genetic information
3. The Hershey-Chase
Experiment
Virus-
nonliving particle that is
much smaller than a cell, that
can infect living organisms
S.E.M. of a T4 bacteriophage virus.
(Reproduced by permission of
Photo Researchers, Inc.)
Bacteriophage-
a type of virus
that infects bacteria.
Are
made of a DNA or RNA core
surrounded by a protein coat
S.E.M. of bacteriophages attacking a bacterium
When
bacteriophages goes inside a
bacterium
 The
virus attaches to the cell surface
 The virus then injects its DNA or RNA
into the bacteria.
 The genes of the virus make the
bacterium produce more viruses
 The result is the bacterium “pops” & is
destroyed & hundreds of new viruses
burst out.
Radioactive
Markers- used to track
a substance inside an organism.
Hershey & Chase were trying to
figure out if genes were made of
protein or DNA.
 They
wanted to figure out which
part of the virus (the protein coat or
DNA core) went inside the
bacterium
Hershey
& Chase used two radioactive
markers to find out
 Sulfur-35 (35S)
tracks or marks proteins
 Phosporous-32 (32P) tracks or marks DNA.
 If 35S
was found in the bacteria, it
would mean that the viruses’
protein had been injected into the
bacteria.
If 32P was found in the bacteria, then it was the
DNA that had been injected.
 Result:
Nearly all the radioactivity in the
bacteria was from phosphorus (32P).
 Conclusion:
The genetic material of the
bacteriophage was DNA not protein.
4. The Components &
Structure of DNA
 DNA
A
is
long molecule
 Made of units called nucleotides
 The nucleotides have 3 parts: deoxyribose,
a phosphate group, & a nitrogenous base
(has nitrogen in it).
There are four kinds of nitrogenous bases in
DNA:
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)
Chargaff’s Rules:
A
biochemist named Erwin Chargaff
studied the amount of each base in
DNA.
 He concluded the following:
 The
% of Guanine (G) is always equal to
the % of Cytosine (C)
 The % of Adenine (A) is always equal to
the % of Thymine (T)
 This is the same in all organisms
X-Ray Evidence
A
scientist named
Rosalind Franklin
studied DNA
 X-ray diffraction; a
technique she used
to learn about the
structure of DNA
The Double Helix
2
scientist named
Watson & Crick
studied the structure
of DNA using 3-D
models
 They used R.
Franklin’s picture &
built a 3-D model out
of wire & cardboard
 A double helix in
which 2 strands are
wound around each
other
 Pg.
292-293 Look at the timeline answer
the following questions:


Why did no DNA discoveries b/w the 1920’s
and 50’s?
Why did discovery speed up during the
1950’s?
 They
discovered that hydrogen bonds form
b/w the nitrogen bases
 This
is what holds the 2 strands together (H
bonds)
 Base
Pairing- H bonds only form b/w
adenine (A) & thymine (T); and cytosine (C)
and guanine (G)
 Base Pairing explains Chargaff’s Rules