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12-3 RNA and protein synthesis
The Central Dogma
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RNA and DNA
DNA• Double helix strands
• Deoxyribose
• A,T,C,G
• Nucleus
RNA• One strand
• Ribose
• A,U (uracil), C,G
• Cytoplasm & nucleus
Strands
Sugar
Base
Location
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DNA ( A T C G)
RNA (A U C G)
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A. messenger RNA (mRNA)B. transfer RNA (tRNA)C. ribosome RNA (rRNA)
Three types of RNA
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A cooking book in French
A cooking book in Chinese
The Central Dogma
Steps from DNA to Proteins
Sequence of nucleotides
Sequence of nucleotides
Sequence of amino acids
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Steps from DNA to Proteins
Nuclearmembrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
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Transcription• Synthesize a mRNA molecule along one template
strand of DNA– In nucleus– Starts at promoter (TATA region of DNA)– Ends at terminator – Need enzyme RNA polymerase– When complete, pre-mRNA is released.
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A T C G T A C G A A G T C T A C G G G A C T A T C G
T A G C G A T A G CA T G C T T C A G A T G C C C T
DNA
A C G A A G U C
mRNA
RNA polymerase
Direction of transcription
5 3
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Transcription
• Steps– DNA unzipped by RNA polymerase– RNA polymerase builds RNA by base paring RNA
nucleotides to one strand of DNA– U is used instead of T– RNA is released and leaves the nucleus
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Question
• What would be the complementary RNA strand for the following DNA sequence?
• DNA: GCGTATG
RNA: CGCAUAC
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Question
• What is the enzyme responsible for the production of the RNA molecule?
• RNA Polymerase– Separates the DNA molecule by breaking the H-
bonds between the bases.
– Then moves along one of the DNA strands and links RNA nucleotides together.
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RNA processing
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RNA processing
mature mRNA transcript5’ 3’
3’
poly-A tail
5’snipped out intron snipped out intron
cap
transcription into pre-mRNA
Part of a DNA strand
exon intron exon exonintron3’ 5’
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Translation
• Synthesize a polypeptide chain using the genetic code on mRNA
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Translation
• Key characters– 1) mRNA : provide code– 2) tRNA : bring building blocks– 3) Ribosome (rRNA) : provide site
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1) mRNA
• A linear sequence of nucleotides
• Three nucleotides make a codon – Codon : the genetic code
for a amino acid– 64 codons– AUG: start– UAA, UAG, UGA: stop
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methionine glycine serine isoleucine glycine alanine stopcodon
protein
A U G G G C U C C A U C G G C G C A U A AmRNA
startcodon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
1) mRNA
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2) tRNA
• Delivers amino acids to ribosomes
• One side attached with amino acid
• Another side with anticodon– Anticodon: 3 nucleotides
that can pair with a codon
– 20 different types of amino acids
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amino acidattachment site
U A C
anticodon
methionine amino acid
2) tRNA
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3) rRNA
• Major component of ribosomes
• Ribosome • Place where amino acids are
made into proteins• Small subunit + large subunit• Large subunit has 2 sites for
tRNA
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PSite
ASite
Largesubunit
Small subunit
mRNA
A U G C U A C U U C G
Ribosome
3) rRNA
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Translation
• Three Steps1. initiation: start codon (AUG)2. elongation:3. termination: stop codon (UAG, UAA, UGA)
• Let’s make a PROTEIN!!!!.
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1) Initiation
PSite
ASite
Largesubunit
Small subunit
mRNA
A U G C U A C U U C G
1-tRNA
U A C
aa1
anticodon
codon
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mRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
Aanticodon
hydrogenbonds codon
1-tRNA
U A C
aa1
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2) Elongation
mRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodon
hydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3
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mRNA
A U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
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mRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
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mRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codon
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mRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
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mRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codon
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mRNA
A C A U G U
aa1
aa2
U
primarystructureof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminator or stop codon
3) Termination
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4) End Product
• The end products of protein synthesis is a primary structure of a protein.
– A sequence of amino acid bonded together by peptide bonds.
aa1
aa2 aa3 aa4aa5
aa200
aa199
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Question:
• The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid.
• What would be the DNA base code for this amino acid?
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Answer:
• tRNA - UAC (anticodon)• mRNA - AUG (codon)• DNA - TAC