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DNA
1
Discovery
of DNA
• Many People
contributed
to the
discovery of
DNA.
• Function:
Carried
genetic
material
2
1928
Frederick Griffith
Transformation
• In a series of
experiments with
Diplococcus
pneumonia
(bacterium
responsible for
pneumonia),
witnessed a
miraculous
transformation.
•These experiments are recognized as the first in a
series that lead to the conclusion that DNA is the 3
carrier of genetic information, the genetic material.
1944
Avery
• Repeated Griffith’s experiment
• Looking for “what” is being
transferred.
• Used enzymes to break up
carbohydrates, lipids and proteinstransformation still took place
• Used enzymes to break up DNAtransformation did not happen
• Conclusions: genes are composed
of DNA
4
1952
Hershey and Chase
• Studying virus
• Wanted to know if proteins or DNA
carried genetic information.
• Used radioisotopes as markers on the
viruses protein coat.
• Allowed virus to infect the bacteria, and
then tested the bacteria for the markers.
• Almost all of the bacteria has the marker.
• Conclusion: The genetic material is DNA
not protein.
5
HersheyChase
experiment
6
1952
Rosalind Franklin
• Used x-ray
diffraction to
see that the
DNA is
twisted like a
spiral
staircase
7
1952
Erwin Chargaff
• Discovered that the
amt. of adenine = amt.
Thymine & the amt. of
cytosine = amt. of
cytosine.
• True in all organisms
tested.
• At this point, he still
didn’t know why.
• This is called
Chargaff’s Rule.
8
Watson and Crick
1953
“Put it all
together”
Developed
the
structure
of DNA
that we
know
today.
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10
Shape of DNA
1. Double Helix.
-Twisted ladder or
spiral staircase
2. Two stranded
3. Held together by
hydrogen bonds
4. Made of four
Nucleotides
11
Structure of DNA
Remember:
• DNA is a nucleic acid.
• Nucleic acids are made of nucleotides.
CLIP
12
Nucleotides
• DNA is a long
chain of
Nucleotides
• There are four
nucleotide that
make up DNA
• Each nucleotide
has three parts:
a sugar molecule,
a phosphate
group, and a
nitrogenous
base.
• The sugar is
Deoxyribose
• There are four bases
13
4 Bases
•
•
•
•
Adenine
Guanine
Cytosine
Thymine
• Purines
• Pyrimidines
14
Sides of
the
“Ladder”
are made
up of
sugar and
phosphate.
15
Adenine always pairs with Thymine
Cytosine always pairs with Guanine
16
Would
Thymine
be able
to pair
up with
Guanine?
17
•
18
CLIP
19
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21
DNA Replication
• Before mitosis, the DNA must be
replicated exactly.
• Each strand can be used to make
the other strand.
• Many enzymes are involved.
22
Chromosome Structure
• DNA is packed very tightly in the
nucleus.
• Human nucleus has 1 meter of
DNA!
• Smallest human chromosome has
30 million base pairs.
• A chromosome has DNA and
protein-chromatin.
• Tiny sections of DNA are called
genes
23
Steps:
• The two
parent
strands
are
unwound
with the
help of
DNA
helicases.
Replication
Bubble
24
25
2. DNA
polymerase
attached
new
nucleotides
to the part
strands
26
• As the DNA strands unwind and separate, new complementary strands are
produced by the hydrogen bonding of free DNA nucleotides with those on
each parent strand.
• As the new nucleotides line up opposite each parent strand by hydrogen
bonding, enzymes called DNA polymerases join the nucleotides .
27
DNA replication website
28
How a protein is
made
29
DNA codes for all of the
cell proteins.
30
• DNA is located in the Nucleus
• Proteins are made on the ribosomes.
• DNA makes a copy (send a message) called “mRNA”
31
Two Steps of Protein Synthesis
1. Transcription
2. Translation
32
Transcription
• During transcription a copy of the DNA
is made…the copy is called messenger
RNA or mRNA. The mRNA takes the
code to the ribosome.
33
DNA vs. RNA
• Double
Stranded
• AGTC
• Deoxyribose
• NEVER!
34
• Single
Stranded
• AGUC
• Ribose
• YES!
• During transcription the DNA unzipped and
RNA nucleotide are paired up with the DNA
bases.
• Website
36
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• Once the mRNA copy is made, it can
go to the ribosome to be translated.
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• Remember
….Proteins
are made
out of
amino
acids.
• There are
20
different
amino
acids.
• 3 bases
code for
each amino
acid.
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• Once the
mRNA get to
the ribosome,
the protein
can be
assembled.
• Transfer
RNA brings
the amino
acids to the
ribosome.
• Website
42
• The three letter code on the mRNA is
called a codon.
• The three letter code on the tRNA that is
matched up with the mRNA is called an
anticodon.
43
Review Clip
Mutations
• A sudden change in the genetic
code is called a mutation.
• Most mutations have little or no
effect on the organism.
• Mutations can be spontaneous or
may be caused by environmental
factors called mutagens.
46
Mutations in DNA usually occur through
one of two processes:
1- DNA damage from environmental agents such as
ultraviolet light (sunshine), nuclear radiation or
certain chemicals.
2- Errors that occur when a cell replicates its DNA in
preparation for cell division.
47
A substitution
mutation is a
simple change in a
single base of the
gene sequence.
48
Frame-shift Mutations
In a frame-shift mutation, one or
more bases are deleted or
inserted, the equivalent of adding
or removing letters in a sentence.
49
In an________ mutation, and
entire section of DNA is
____________.
Review of DNA Mutations
Harmful, Helpful, Neutral
• Substitutions
• Frameshift
– Deletions
– Insertions
• Causes:
CLIP
– Mutagens
• UV light
• Radiation
• Free radicals
• Chemicals (ex: substances in tobacco products)
– Replication errors
36
Which of the following
is the correct basepairing rule for DNA?
A A-U; C-G
B A-G; T-C
C A-T; G-C
D A-C; T-G
DNA
TECHNOLOGY
genetic recombination.
There are many uses for DNA technology. Police labs
use DNA technology to identify people through a
process known as DNA fingerprinting.
Today, researchers use recombinant DNA
technology to analyze genetic changes. They
cut, splice together, and insert the modified
DNA molecules from different species into
bacteria or another type of cell that rapidly
replicates and divides. The cells copy the
foreign DNA right along with their own DNA.
An example of this is the gene for human
insulin. When the gene is transferred into a
bacterium, the bacterium will use the
“recombined” genetic code to produce human
insulin. This is how human insulin is mass
produced.
Not only does genetic engineering have
applications in medicine and the
environment, it also has uses in industry
and agriculture. Sheep are used in the
production of alpha-1 antitrypsin, which is
used in the treatment of emphysema. Goats
are also producing the CFTR protein used in
the treatment of cystic fibrosis.
In the plant world, the buds of cotton
plants are vulnerable to worm
attacks. The buds of a modified
cotton plant resist these worms,
resulting in increased cotton
production.
These gene insertions are
ecologically safer than pesticides.
They affect only the targeted pest.
Plant biologists have used DNA
technology to produce plants
with many desirable traits.
These include increased disease
resistance, herbicide resistance,
and increased nutritional
content.
Clip
Scientists today have developed genetically
altered bacteria.
Among them are strains of bacteria that
eat up oil spills
manufacture alcohol and other
chemicals
process minerals.
There is concern about possible risks to the
environment and the general population as
genetically engineered bacteria are
introduced.