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DNA and RNA
Replication, Transcription, and
Translation
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Genetic Controversy
Two schools of thought
a. Some said protein was material
b. Some said DNA was material
How was the controversy settled?
- The scientific experiments of Griffith, Avery,
Hershey and Chase
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Griffith and Transformation
- 1928 - England
- Trying to develop a
vaccine against
pneumonia causing
bacteria
- Two strains - S(smooth)
and R(rough)
3
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Dies of pneumonia
Harmless bacteria
(rough colonies)
Lives
Heat-killed, diseasecausing bacteria
(smooth colonies)
Lives
Control
(no growth)
Live, disease-causing
bacteria (smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia
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RESULTS
- Showed that heat killed S strain
and live R strain would kill mice
- Something was “transforming”
the R strain to an S strain
- Called it transformation
- What was the material?
5
Oswald Avery - 1944
- Wanted to identify Griffith’s transforming material
- Used two enzymes
a. protein killing
b. DNA killing
- Showed that no transforming took place when DNA
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D. Hershey and Chase
- 1952
- Working with a
bacteriophage
- Virus that infects
bacteria
- Made of only two
things
a. protein coat
b. DNA (genetic) core
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Hershey and Chase
Bacteriophage with
phosphorus-32 in
DNA
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
Radioactivity inside bacterium
Phage infects
bacterium
No radioactivity inside bacterium
9
Recap:
Was DNA or protein injected?
- DNA has phosphorus
- Protein has sulfur
- Used radioactive phosphorus 32P
and radioactive sulfur 35S
- Let virus infect bacteria
- New viruses full of 32P
DNA was being injected!
10
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The Components and Structure of
DNA
1. Called deoxyribonucleic acid
2. Long and thread-like (twisted)
3. Many subunits linked together
4. Subunits called nucleotides
5. 1000’s in a chain-like structure
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The structure of a nucleotide
1. Phosphate group - same in all
2. Five carbon sugar
a. deoxyribose sugar
3. Nitrogenous base - 4 different
ones that name the nucleotide
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Nitrogenous Bases
1. Are different in each
nucleotide
2. Names of the four
bases
a. adenine (A)
b. guanine (G)
c. thymine (T)
d. cytosine (C)
Two classes of bases
A. purines
1) large double
ring
2) A & G
B. pyrimidines
1) small single
ring
2) T & C
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Purine and Pyrimidine Structure
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H. Chargaff - 1949
- Studying the amounts of
bases in DNA of living
things
- His results showed that:
a. A always = T
b. C always = G
- Called Chargaff’s rule
- Also called the base pair
rule
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The molecule is completed…
- Franklin and her X-ray
diffraction picture showed
a helix
- Watson and Crick adds
that it is a double helix
with bases in the middle
- Called it a “spiral
staircase”
- Strands are
complements of
each other
- Think of a step ladder
a. “sides” are alternating
sugar and phosphate
groups
b. “rungs” are base pairs
1) A = T
2) C = G
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Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Adenine
Thymine
Cytosine
Guanine
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Chromosomes and DNA Replication
A. DNA Can Make Copies of Itself
1. Process called replication
2. Done during S phase
3. Needed for new cells
4. DNA unwound using helicases
5. Hydrogen bonds broken between bases
6. DNA polymerase puts new nucleotides in
place (A to T and C with G)
7. New copy just like original
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From Genes To Proteins
 DNA
 RNA
 Double-stranded
 Single-stranded
 Deoxyribose
 Ribose
 Thymine
 Uracil
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RNA
(ribonucleic acid)
3 forms of RNA
 mRNA (messenger)
 tRNA (transfer)
 rRNA (ribosomal)
RNA is used to take the information in DNA and make proteins
(gene expression)
2 stages of gene expression
 Transcription
 Translation
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The Big Idea…
During gene expression, the info
in DNA is first transcribed as
mRNA and then translated via
tRNA and used to build a
protein.
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From Genes To Proteins…
1. Transcription:
making mRNA
from DNA to
carry information
to the ribosomes.
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- ALL organisms
have a genetic code
made of three
nucleotide
sequences called
codons.
QuickTime™ and a
decompressor
are needed to see this picture.
- Codons correspond
to particular AA
and stop signals.
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The Genetic Code
QuickTime™ and a
decompressor
are needed to see this picture.
The Genetic Code
QuickTime™ and a
decompressor
are needed to see this picture.
26
From Genes To Proteins…
2. Translation:
Using tRNA to build
proteins from the
information in
mRNA.
- Each tRNA molecule
carries an amino acid to
the ribosomes, by
matching its anticodon to
a specific codon from the
mRNA
http://www.youtube.com/watch?v=NJxobgkP
EAo
GENETIC MUTATIONS
Mutations (gene or chromosomal)
 Changes
in DNA
 Effect depends on where mutation occurs
(body or sex cell) & what type of mutation
 Can be helpful, harmful, or neutral
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Different Types of Gene
Mutations

Substitutions = UGU to UGC
 Effect depends on translation

Insertions = nucleotides added

Deletions = nucleotides deleted

Transposons= DNA segments move spontaneously from
one location to another in the same DNA molecule
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 Ex.
THE CAT ATE THE RAT
(meaningful)
 Deletion
of C =
THE ATA TET HER AT
(meaningless)
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Types of Chromosomal
Mutations

Deletions (whole or part deleted)

Duplications (extra copies of parts)

Inversions (reverses parts of chromosomes)

Translocations (parts break off and relocate)
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Causes of Mutations?
 Spontaneous
 Mutagens (come from environment)
 UV light
 Chemicals
 Carcinogens (cancer causing)
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