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DNA (Deoxyribonucleic Acid)
Transformation of Bacteria
Transformation of Bacteria
Chromosomes are made of DNA and protein
What carries hereditary information?
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By the 1940s, scientists knew that
chromosomes carried genes.
They also knew that chromosomes were
made of DNA and protein.
They did NOT know which of these
molecules actually carried the genes.
Since protein has 20 types of amino acids
that make it up, and DNA only has 4 types
of building blocks, it was a logical
conclusion.
Most Scientists thought protein carried
genes
Avery’s Experiment
1. Avery repeated Griffith’s
experiments with an
additional step to see what
type of molecule caused
transformation.
3. When Avery added
enzymes that destroy
DNA, no transformation
occurred.
So…he knew that
DNA carried
hereditary
information!
2. Avery used enzymes to destroy the sugars and
transformation still occurred—Sugar did not cause
transformation.
Avery used enzymes to destroy lipids, RNA, and
protein one by one. Every time transformation still
occurred—none of these had anything to do with
the transformation.
Hershey-Chase Experiment
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The experiment involved viruses
to see if DNA or protein was
injected into the bacteria in
order to make new viruses.
One group of viruses was
infected with radioactive
protein and another group with
radioactive DNA.
Then the viruses attack the
bacteria.
Radioactive DNA shows up in
the bacteria, but no
radioactive protein.
Chargaff’s Rules
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The amount of adenine
(A) equals the amount of
thymine (T).
The amount of cytosine
(C) equals the amount of
guanine (G).
Rosalind Franklin
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Took X-ray
pictures of DNA.
The photos
revealed the
basic helix,
spiral shape of
DNA.
Maurice Wilkins
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Worked with
Rosalind Franklin.
Took her x-ray
photos and
information to
Watson and Crick
Watson and Crick
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Used Franklin’s pictures
to build a series of
large models.
Stated that DNA is a double-stranded molecule in
the shape of a double helix, or twisted ladder.
Won the Nobel Prize for their work in 1962.
Basic DNA Structure
P

S
A
P
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S
P
C
A nucleotide is
theTmonomer of
S
DNA
A nucleotide is
made
G of
S
– a sugar called
deoxyribose
T
– aA phosphate
S
S
– and a base
 The two strands of DNA are held
(ATCG)
together by hydrogen bonds
P
P
P
DNA Replication
DNA makes a copy of itself.
1. The DNA
molecule
separates into
its 2 strands by
breaking the
hydrogen
bonds.
2. Each old
strand
becomes a
template for
a new
strand.
3. An enzyme called
DNA polymerase
adds new
complementary
nucleotides to each
original strand.
DNA Splits
P
S
A
T
S
P
P
S
C
G
S
P
P
S
T
A
S
P
Add New Nucleotides
Fill in the correct nucleotides that will be added.
P
P
S
A
T
S
S
P
P
S
C
G
S
T
A
P
C
G
S
P
P
S
S
S
P
S
P
T
P
S
P
A
T
A
S
P
Questions
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Are the two copies of DNA the
same?
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Why would it be important for the two
copies of DNA to be the same?
What is a Gene?
A gene is a
code found in
DNA
 Genes code
for proteins
that give
people their
traits.
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How does DNA code for so
many traits with only 4 bases?
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Can you spell 20 words
with the letters A, T, C
and G?
Each combination of
bases codes for a
different amino acid.
Putting the 20 amino
acids in different orders
makes different
proteins.
What organelle makes proteins?
Ribosomes
Which molecule makes proteins?
RNA
RNA
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Single-stranded nucleic acid
Made of nucleotides
Has ribose instead of deoxyribose
Has uracil instead of thymine
Transcription
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DNA’s code is transcribed onto mRNA.
mRNA has complementary bases to the DNA.
Each codon is made of three bases.
Translation
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Translation begins at the start codon (AUG)
of mRNA
Then each codon codes for an amino acid in
a protein that is brought in by a tRNA.
tRNA has complementary bases to mRNA
Translation is terminated by stop codon.
Which Amino Acid does each codon
code for?
GGU
Glycine
 AAA
Lysine
 CUG
Leucine
 UGG
Tryptophan
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Mutations
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Mutation-alteration in
DNA
Mutagens-physical and
chemical agents that
mutate DNA
Deletion-mutation caused by deleting DNA
that should be there
Insertion-mutation caused by inserting DNA
that should not be there
Substitution-mutation caused by substituting
DNA
Inversion-DNA is inverted or flipped
Gene Regulation
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Genes are not expressed all the time.
Some genes are usually on, but can
be turned off by repressors when they
are not needed.
Some genes are usually off, but they
can be turned on by enhancers when
they are needed.
The End!