protein synthesis notes ch 17 central dogma dna rna protein
TRANSCRIPT
Protein Synthesis Notes
Ch 17
Central Dogma
• DNA RNA Protein
Prokaryotic vs Eukaryotic Transcription
Prokaryotic Transcription-takes place in cytoplasm -circular DNA w/no histones-no introns / no mRNA processing
Eukaryotic Transcription -takes place in nucleus -DNA has histones and linear-introns and mRNA processing
Prokaryotic Transcription
1. Initiation – RNA polymerase binds to promoter
2. Elongation – RNA polymerase reads template 3’-5’ and builds mRNA strand 5’-3’
3. Termination – mRNA is released …forms hairpin loop.
STEPS
Eukaryotic Transcription1. Initiation – Transcription factors
adhere to the TATA box in the promoter signaling RNA Polymerase II to attach. Additional transcription factors attach and the transcription initiation complex is formed. Enhancers/silencers
2. Elongation – RNA Polymerase II unzips the DNA and pairs the template withcomplementary mRNA nucleotides.
3. Termination – RNA Polymerase II reaches the polyadenylation (AAUAAA)
sequence and releases the pre-mRNA.
*Gene expression is most often regulated at transcription
transcription
Eukaryotic TranscriptionHHMI transcription initiation complex
Transcription
mRNA processing
mRNA Processing (takes place in the nucleus)1. Add 5’ cap (guanine with 3 phosphates) 2. Add Poly A tail (repeated Adenines)3. Introns (non coding regions) cut out4. Exons (coding regions) fused together
snRNPs (small nuclear ribonucleoproteins)
• snRNPs- small nuclear RNA– RNA and proteins
• Spliceosome - several snRNPs that carry out RNA splicing
Spliceosome Animation
RibozymeRibozyme – RNA that functions as an enzyme-splicing without proteins!
How: 1. Single stranded and forms 3-D structure2. Bases in RNA contain functional groups that may catalyze rxns. 3. Forms hydrogen bonds
Sidney Altman Thomas CechYale U of Colorado
Harvard Ribozymes
Thomas-Cech Ribozymes
Animations• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf• http://www.concord.org/~btinker/workbench_web/models/eukTranscription.swf• http://vcell.ndsu.edu/animations/transcription/index.htm• http://www.hhmi.org/biointeractive/dna/animations.html
2007-2008
Translationfrom
nucleic acid languageto
amino acid language
Translation • Codons– 3 nucleotides
decoded into the sequence of amino acids
2007-2008
Translation in Prokaryotes
Bacterial chromosome
mRNA
Cell wall
Cellmembrane
Transcription
Translation
proteinPsssst…no nucleus!
• Transcription & translation are simultaneous in bacteria – DNA is in
cytoplasm– no mRNA
editing – ribosomes
read mRNA as it is being transcribed
Translation in Prokaryotes
Translation: prokaryotes vs. eukaryotes• Differences between prokaryotes &
eukaryotes– time & physical separation between processes• takes eukaryote ~1 hour
from DNA to protein– RNA processing
2007-2008
Translation in Eukaryotes
mRNA
From gene to protein
DNAtranscription
nucleus cytoplasm
mRNA leaves nucleus through nuclear pores
proteins synthesized by ribosomes using instructions on mRNA
aa
aa
aaaa
aa
aaaa
aa
ribosome
proteintranslation
How does mRNA code for proteins?TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
Met Arg Val Asn Ala Cys
Alaprotein
?
4
4
20
ATCG
AUCG
AUGCGUGUAAAUGCAUGCGCC
mRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala
Cys Ala
protein
?
codon
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
Why is thewobble good?
2007-2008
Translationfrom
nucleic acid languageto
amino acid language
Translation • Codons– blocks of 3
nucleotides decoded into the sequence of amino acids
2007-2008
Translation in Prokaryotes
Bacterial chromosome
mRNA
Cell wall
Cellmembrane
Transcription
Translation
proteinPsssst…no nucleus!
• Transcription & translation are simultaneous in bacteria – DNA is in
cytoplasm– no mRNA
editing – ribosomes
read mRNA as it is being transcribed
Translation in Prokaryotes
Translation: prokaryotes vs. eukaryotes• Differences between prokaryotes &
eukaryotes– time & physical separation between processes• takes eukaryote ~1 hour
from DNA to protein– RNA processing
2007-2008
Translation in Eukaryotes
mRNA
From gene to protein
DNAtranscription
nucleus cytoplasm
mRNA leaves nucleus through nuclear pores
proteins synthesized by ribosomes using instructions on mRNA
aa
aa
aaaa
aa
aaaa
aa
ribosome
proteintranslation
How does mRNA code for proteins?TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
Met Arg Val Asn Ala Cys
Alaprotein
?
4
4
20
ATCG
AUCG
AUGCGUGUAAAUGCAUGCGCC
mRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala
Cys Ala
protein
?
codon
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
Why is thewobble good?
How are the codons matched to amino acids?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
aminoacid
tRNA
anti-codon
codon
5 3
3 5
3 5
UAC
MetGCA
ArgCAU
Val
mRNA
From gene to protein
DNAtranscription
nucleuscytoplasm
aa
aa
aaaa
aa
aaaa
aa
ribosome
proteintranslation
aa
Transfer RNA structure• “Clover leaf” structure– anticodon on “clover leaf” end– amino acid attached on 3 end
tRNA – “Wobble”
Inosine can pair with C, A, U allowing for less tRNA’s, More relaxed at the 3rd base position.
Loading tRNA • Aminoacyl tRNA synthetase – enzyme which bonds amino acid to tRNA– bond requires energy
• ATP AMP– energy stored in tRNA-amino acid bond
• 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
Ribosomes • Facilitate coupling of
tRNA anticodon to mRNA codon
• Structure– ribosomal RNA (rRNA) & proteins– 2 subunits• large• Small
E P AAssembled in the nucleus of Eukaryotes
Ribosomes
Met
5'
3'
UUA C
A G
APE
• A site (aminoacyl-tRNA site) – holds tRNA carrying next amino acid to be
added to chain • P site (peptidyl-tRNA site) – holds tRNA carrying growing polypeptide chain
• E site (exit site)– empty tRNA
leaves ribosome from exit site
Translation Animation McGraw HillUconn Translation Animation
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'
Protein targeting • Signal peptide– address label
Destinations: secretion nucleus mitochondria chloroplasts cell membrane cytoplasm etc…start of a secretory pathway
Can you tell the story?
DNA
pre-mRNA
ribosome
tRNA
aminoacids
polypeptide
mature mRNA
5' cap
polyA tail
large ribosomal subunit
small ribosomal subunit
aminoacyl tRNAsynthetase
E P A
5'
3'
RNA polymerase
exon introntRNA