PROTEIN SYNTHESIS
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PROTEIN PROTEIN SYNTHESISSYNTHESIS
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3 Types of RNA• mRNA= messenger• tRNA= transfer• rRNA= ribosomal
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The Central Dogma• DNA
– The master program of the cell
– Never leaves the nucleus
• Transcription– Process that makes mRNA
from DNA– Takes place in the nucleus
• Translation– Process that makes proteins
from mRNA– Takes place in the cytoplasm
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Steps in Steps in TranscriptionTranscription
InitiationInitiation ElongationElongation TerminationTermination
When complete, When complete, pre-RNApre-RNA molecule is releasedmolecule is released
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TranscriptionTranscription
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Question:Question:
What would be the What would be the complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA sequence?
DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’
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RNA ProcessingRNA Processing
pre-RNA molecule
intron
intronexon exon exon
exon exon exon
Mature RNA moleculeMature RNA molecule
exon exon exon
intron intron
splicesome splicesome
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TranslationTranslation
•Synthesis of proteinsSynthesis of proteins in the in the cytoplasmcytoplasm
• Involves the following:Involves the following:
1.1. mRNA (codons)mRNA (codons)
2.2. tRNA (anticodons)tRNA (anticodons)
3.3. ribosomesribosomes
4.4. amino acidsamino acids
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TranslationTranslation• Three steps:Three steps:
1.1. initiationinitiation: start codon (AUG): start codon (AUG)
2.2. elongationelongation: amino acids : amino acids linkedlinked
3.3. terminationtermination: stop codon : stop codon (UAG, UAA, or UGA).(UAG, UAA, or UGA).
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mRNA Codons Join the mRNA Codons Join the RibosomeRibosome
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
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InitiationInitiation
mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogenbonds codon
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mRNAmRNA
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
ElongationElongation
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mRNAmRNA
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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mRNAmRNA
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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mRNAmRNA
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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mRNAmRNA
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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mRNAmRNA
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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mRNAmRNA
A C A U G U
aa1
aa2
U
primaryprimarystructurestructureof a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator or stopor stop codoncodon
TerminationTermination
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End Product –The End Product –The Protein!Protein!
• The end products of protein The end products of protein synthesis is a synthesis is a primary structureprimary structure of a proteinof a protein
• A A sequence of amino acidsequence of amino acid bonded together by peptide bonded together by peptide bondsbonds
aa1
aa2 aa3 aa4aa5
aa200
aa199
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Question:Question:
What would be the Amino What would be the Amino acid sequence for the acid sequence for the following mRNA strand?following mRNA strand?
mRNA mRNA CGAUGUUCAGACGCGGGUACGAUGUUCAGACGCGGGUA
ACGACG
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