Chapter 17 From Gene to Protein (Protein Synthesis) From Gene to Protein (Protein Synthesis)
AP Details for Protein Synthesis
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AP Details for Protein Synthesis
2014
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From gene to protein
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AP Biology
Transcriptionfrom
DNA nucleic acid languageto
RNA nucleic acid language
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Transcription• Making mRNA– transcribed DNA strand = template strand– untranscribed DNA strand = coding strand
• same sequence as RNA– synthesis of complementary RNA strand
• transcription bubble– Enzyme involved
• RNA polymerase
template strand
rewinding
mRNA RNA polymerase
unwinding
coding strand
DNAC C
C
C
C
C
C
C
C CC
G
GG
G
G G
G G
G
G
GAA
AA A
A
A
A
A
A A
A
AT
T T
T
T
T
T
T
T T
T
T
U U
5
35
3
3
5build RNA 53
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RNA polymerases• 3 RNA polymerase enzymes– RNA polymerase 1• only transcribes rRNA genes• makes ribosomes
– RNA polymerase 2• transcribes genes into mRNA
– RNA polymerase 3• only transcribes tRNA genes
– each has a specific promoter sequence it recognizes
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Which gene is read?• Promoter region– binding site before beginning of gene – TATA box binding site– binding site for RNA polymerase
& transcription factors
– Enhancer region– binding site for
activators (activate genes)
– Silence region– Binding site for
repressors (turns genesoff)
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What are Transcription Factors?• Initiation complex– transcription factors bind to promoter region
• suite of proteins which bind to DNA• turn on or off transcription
– trigger the binding of RNA polymerase to DNA
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Matching bases of DNA & RNA• Match RNA bases to DNA
bases on one of the DNA strands
U
A G GGGGGT T A C A C T T T T TC C C CA A
U
UU
U
U
G
G
A
A
A C CRNA polymerase
C
C
C
C
C
G
GG
G
A
A
A
AA
5' 3'
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Eukaryotic genes have junk!• Eukaryotic genes are not continuous– exons = the real gene• expressed / coding DNA
– introns = the junk• inbetween sequence
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
intronscome out!
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mRNA splicing
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
primary mRNAtranscript
mature mRNAtranscript
pre-mRNA
spliced mRNA
• Post-transcriptional processing – eukaryotic mRNA needs work after transcription– primary transcript = pre-mRNA– mRNA splicing• edit out introns
– make mature mRNA transcript
~10,000 bases
~1,000 bases
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Splicing must be accurate• No room for mistakes!– a single base added or lost throws off the reading
frame
AUG|CGG|UCC|GAU|AAG|GGC|CAU
AUGCGGCTATGGGUCCGAUAAGGGCCAUAUGCGGUCCGAUAAGGGCCAU
AUG|CGG|GUC|CGA|UAA|GGG|CCA|U
AUGCGGCTATGGGUCCGAUAAGGGCCAUAUGCGGGUCCGAUAAGGGCCAU
Met|Arg|Ser|Asp|Lys|Gly|His
Met|Arg|Val|Arg|STOP|
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RNA splicing enzymes
snRNPs
exonexon intron
snRNA
5' 3'
spliceosome
exonexcisedintron
5'
5'
3'
3'
3'
lariat
exonmature mRNA
5'
No, not smurfs!“snurps”
• snRNPs– small nuclear RNA
• Spliceosome– several snRNPs– recognize splice site
sequence• cut & paste gene
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A A AA
A3' poly-A tail
mRNA
5'5' cap
3'
G PPP
50-250 A’s
More post-transcriptional processing
• Need to protect mRNA on its trip from nucleus to cytoplasm– enzymes in cytoplasm attack mRNA
• protect the ends of the molecule• add 5 GTP cap
– Chemically modified molecule of GTP– It facilitates the binding of mRNA to the ribosome and protects the mRNA
from being digested by ribonucleases – enzymes in cytoplasm that break down RNA
• add 3’poly-A tail– longer tail – 100-300 adenine nucleotides– Assists in export of mRNA from nucleus – Important in mRNA stability
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Radjewski
Translationfrom
nucleic acid languageto
amino acid language
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The code• Code for ALL life!
– strongest support for a common origin for all life
• Code is redundant– several codons for each
amino acid– 3rd base “wobble”
Start codon AUG methionine
Stop codons UGA, UAA, UAG
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Transfer RNA structure• “Clover leaf” structure– anticodon on “clover leaf” end– amino acid attached on 3 end
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Loading tRNA • Aminoacyl tRNA synthetase – enzyme which bonds amino acid to tRNA– bond requires energy
• ATP AMP• bond is unstable• so it can release amino acid at ribosome easily
activatingenzyme
anticodontRNATrp binds to UGG condon of mRNA
Trp Trp Trp
mRNAA C CU G G
C=OOH
OHH2OO
tRNATrp
tryptophan attached to tRNATrp
C=O
O
C=O
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Building a polypeptide• Initiation
– brings together mRNA, ribosome subunits, initiator tRNA
• Elongation– adding amino acids based on codon
sequence
• Termination– end codon 123
Leu
Leu Leu Leu
tRNA
Met MetMet Met
PE AmRNA
5' 5' 5' 5'3' 3' 3' 3'
U UA A AACC
CA U UG G
GUU
A AAAC
CC
A U UG GGU
UA A A
ACC
CA U UG G
GU UA A ACCA U UG G
G A C
Val Ser
Ala Trp
releasefactor
AA A
C CU UG G 3'
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Protein targeting • Signal peptide– address label
Destinations: secretion nucleus mitochondria chloroplasts cell membrane cytoplasm etc…
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Can you tell the story?
DNA
pre-mRNA
ribosome
tRNA
aminoacids
polypeptide
mature mRNA
5' GTP cap
poly-A tail
large ribosomal subunit
small ribosomal subunit
aminoacyl tRNAsynthetase
E P A
5'
3'
RNA polymerase
exon introntRNA
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AP Biology
Protein Synthesis in Prokaryotes
Bacterial chromosome
mRNA
Cell wall
Cellmembrane
Transcription
Psssst…no nucleus!
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Prokaryote vs. Eukaryote genes• Prokaryotes– DNA in cytoplasm– circular chromosome– naked DNA
– no introns
• Eukaryotes– DNA in nucleus– linear chromosomes– DNA wound on histone
proteins– introns vs. exons
eukaryoticDNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
intronscome out!
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• Transcription & translation are simultaneous in bacteria – DNA is in
cytoplasm– no mRNA
editing – ribosomes
read mRNA as it is being transcribed
Translation in Prokaryotes
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Translation: prokaryotes vs. eukaryotes• Differences between prokaryotes &
eukaryotes– time & physical separation between processes• takes eukaryote ~1 hour
from DNA to protein– no RNA processing
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AP Biology
Any Questions??What color would a smurf turnif he held his breath?