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DNA & RNA Lecture II
Using the Code of Life
DNA & RNA
1
Two process involve DNA
1. Replication: making an exact copy of DNA
 purpose: reproduction
 occurs: nucleus
 uses: only DNA
2. Protein Synthesis: production of proteins
 purpose: growth & reproduction
 occurs: between nucleus & ribosomes
 uses: both DNA & RNA
2
Replication
Making Exact Copies of DNA
3
DNA Unzip
4
Replication of Helix
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Mechanism of Replication Basics
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Replication
• Creates an exact copy DNA
• Steps:
1. DNA unzips
2. “Free-floating” nucleotides
in cytoplasm fill slots along
existing strand of DNA
3. Two double strands formed.
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Replication
• A more detailed diagram.
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Comparing DNA & RNA
DNA
• Double stranded
• Deoxyribose Sugar
• Phosphate
• Nitrogenous bases
–
–
–
–
Adenine
Cytosine
Thymine
Guanine
RNA
• Single stranded
• Ribose Sugar
• Phosphate
• Nitrogenous bases
–
–
–
–
Adenine
Cytosine
Uracil
Guanine
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Protein Synthesis
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Why Do We Need Proteins?
1. Cell Structure
• Cell = 80% protein
Cell membrane
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Why Do We Need Proteins?
2. Cell Processes
• Hormones (signals)
• Enzymes (speed up reactions)
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Why Do We Need Proteins?
3. Membrane Channels (remember
transport?)
4. Neurotransmitters
(carry nerve/brain
messages)
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What Do We Need For
Protein Synthesis?
1. DNA
 Template for making
mRNA during
Transcription
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What Do We Need For
Protein Synthesis?
2. RNA
a) mRNA — messenger RNA
makes & takes copy of
DNA to cytoplasm.
b) tRNA — transfer RNA
Matches w/ mRNA on
ribosome. Carries AA to
add to protein chain.
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What Do We Need For
Protein Synthesis?
3. Ribosome
Reads mRNA
Directs tRNA
Creates peptide bonds between AAs
makes polypeptide (protein) chain
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What Do We Need For
Protein Synthesis?
4. Amino Acids (AAs)
• Building blocks of
proteins (20 AAs
exist)
• Protein = AA chain =
polypeptide chain
• ORDER MATTERS!
AA order determines
function of protein
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Amino Acids
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Steps of Protein Synthesis
1. Transcription (writing the “message”)
DNA makes mRNA
 messenger carries code to
cytoplasm
2. Translation (reading the “message”)
mRNA and tRNA make protein (AA chain)

message translated into a protein
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Steps of Protein Synthesis
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Steps of Protein Synthesis
(Nucleus)
(Cytoplasm)
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Transcription
Transferring the DNA Code to mRNA
DNA to mRNA
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Transcription — Basics
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Transcription
DNA to mRNA
Location = nucleus
1. Enzyme binds to DNA, unzips it
2. mRNA makes a copy of gene from DNA
template
*U replaces T in RNA
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Transcription
3. A codon is a threeletter “word” of
instruction
4. Codons are made
of mRNA
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Transcription
5. They attach to
anticodons at
ribosomes
6. Anticodons are
attached to clover
leaf like structures
which carry a
specific amino
acid.
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Transcription
5. DNA nucleotides (triplet) turn
into mRNA codon
Codons
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Transcription
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Translation
Writing the Code to form Amino Acids
(Proteins)
mRNA to tRNA
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Translation
Decoding (writing) — bonding of amino
acids to form proteins
mRNA and tRNA make protein (AA chain)
Location = cytoplasm
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Translation — Basic
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Translation
Steps of Translation
1. mRNA moves to
cytoplasm, binds to
ribosome
2. tRNA anticodon
brings AA (amino
acid) to mRNA
codon on ribosome
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Translation
3. Ribosome
moves down mRNA to next codon
4. tRNA anticodon picks up & attaches next AA
with peptide bond
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Translation
5.
tRNA leaves ribosome once AA attached
Protein chain
AA
tRNA
mRNA
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Translation
6. Steps
1-5 repeated, adding Aas until STOP
CODON signals end of protein
7. Polypeptide chain (protein) released from
ribosome
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Translation
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
GGA
CCT
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
TAC
AUG
tRNA
Anti-codon
GGA
CCT
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCT
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
CCT
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
CCU
TAT
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
CCU
TAT
AUA
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
CCU
TAT
AUA
UAU
ACT
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
CCU
TAT
AUA
UAU
ACT
UGA
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Synthesis Practice
DNA
Triplet
mRNA
Codon
tRNA
Anti-codon
TAC
AUG
UAC
GGA
CCU
GGA
CCT
GGA
CCU
TAT
AUA
UAU
ACT
UGA
ACU
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AMINO ACID FUN!!






DNA Triplet: ACC
mRNA codon: UGG
tRNA anti-codon: ACC
Amino acid: Tryptophan
Why you sh
Tryptophan is in TURKEY – makes you sleepy
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Protein Synthesis
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Protein Synthesis Animation
http://www.columbia.edu/cu/biology/course
s/c2005/images/animtransln.gif
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List of Condons & Amino Acids
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List of Amino Acids
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