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PROTEIN
SYNTHESIS
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DNA Replication
Occurs when chromosomes duplicate
An exact copy of the DNA is produced
Hydrogen bonds between bases break and
the molecule “unzips” with helicases
Each old strand of nucleotides serves as
a template for each new strand
New nucleotides move into position
according to Base Pair Rules with DNA
polymerase
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DNA
Replication
Why does DNA replicate?
Where does DNA replicate?
When does DNA replicate?
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Protein Synthesis:
The process of
producing proteins
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Making Proteins!
 DNA carries the instructions
for producing proteins
 Proteins are made of amino
acids linked together
 20 different amino acids exist
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Why proteins?!?
• Antibodies, enzymes and hormones
• Hair, nails, muscles, skin
Where do the amino
acids come from??
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Proteins are made by Ribosomes!
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RNA
• RNA: Single strand that carries
genetic info from the DNA to the
ribosomes!
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RNA Differs from DNA:
1. Sugar = Ribose
2. RNA contains the base Uracil (U)
in place of Thymine (T)
3. Single-stranded
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DNA/RNA Building Analogy
• DNA is the official Master plan!
• RNA is the cheap, disposable
blueprint of the master plan
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The Base Pairs
In RNA:
A always pairs with U
C always pairs with G
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Types of RNA
• Messenger RNA (mRNA) carries
message from DNA to the ribosomes
• Transfer RNA (tRNA) acts like a
tow truck…taking amino acids to
the ribosome
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The Genetic Code
 Genetic language reads 3 letters at a time
 CODON: three consecutive nucleotides that
specify a single amino acid.
U C G C A C G G U
is read as
UCG-CAC-GGU
which codes for
Serine-Histidine-Glycine
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Amino Acid Wheel
Use the code
by reading
from the
center to
the outside
Example: AUG codes for Methionine
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Name the Amino Acids!
• GGG?
• UCA?
• CAU?
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Special Codons
• Some codons are called the “Start
Codons” or “Stop Codons”
– These do not code for an amino acid
– They just indicate the beginning and
end of a protein!
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Protein
Synthesis
1)Transcription
2)Translation
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1) Transcription
Transferring info from DNA to mRNA
The DNA strand separates & one strand
acts as a template for RNA.
-Using rules of base pairs
-Remember U instead of T!
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2) Translation
• The message in the mRNA is converted
into proteins in the ribosome
• The information is being TRANSLATED!
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During Translation:
1) mRNA goes to ribosome
2) Ribosomes read each codon one at
a time
3) tRNA brings supplies for amino
acid
3) Long chains of amino acids make
proteins!
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Making a Protein
DNA
mRNA
tRNA
Protein
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DNA  RNA  Protein
Nuclear
membrane
DNA
Eukaryotic
Cell
Transcription
mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
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(Single Strand)
Transcription
Translation
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Question:
What would be the
complementary RNA strand
for the following DNA
sequence?
DNA = G C G T A T G
RNA =
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Question:
What would be the
complementary RNA strand
for the following DNA
sequence?
DNA = G C G T A T G
RNA = C G C A U A C
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mRNA carries the info!
start
codon
mRNA
A U G G G C U C C A U C G G C G C A U A A
codon 1
protein methionine
codon 2
codon 3
glycine
serine
codon 4
isoleucine
codon 5
codon 6
glycine
alanine
codon 7
stop
codon
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Mutation:
Changes in genetic material
• Like all mistakes, mutations can
vary in shape & size!
– Some mutations are neutral!
– Some mutations are beneficial!
– Some mutations are fatal!
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Mutations can occur naturally or be
caused by environmental factors, such
as:
-X rays
-Drugs
-Chemical exposure
-UV light
-Tobacco
smoke
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• Point Mutations: Involve changes in one
nucleotide and usually don’t cause major
problems.
-Substitution of one base
• Frameshift Mutations: When an entire
nucleotide is added or deleted, all of the
following codons are shifted.
– This may change every single amino acid which
would greatly affect the protein
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Example of Point Mutation
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Example of Frameshift Mutation
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• Mutations in sex cells can be passed down to
offspring and be good or bad!
– Can cause major problems
– May become new genetic variation in a species!
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