Translation How the Genetic Information Is Used to Build a Protein.
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Transcript of Translation How the Genetic Information Is Used to Build a Protein.
Translation Translation
How the Genetic Information Is How the Genetic Information Is Used to Build a ProteinUsed to Build a Protein
DNA
Information Flow From DNA
initial transcript RNA
transcription
Proteintranslation
replication
processing
mature RNA
Properties of the Genetic CodeProperties of the Genetic Code
• TripletTriplet– 3 nucleotides code for 1 amino acid3 nucleotides code for 1 amino acid
• Non-overlappingNon-overlapping– Codons are adjacent to each otherCodons are adjacent to each other
• DegenerateDegenerate– Some amino acids have more than one Some amino acids have more than one
codoncodon
• ““Almost” universalAlmost” universal– A few exceptions occur in mitochondrial, A few exceptions occur in mitochondrial,
bacterial and protist genesbacterial and protist genes
Accurate Protein Synthesis Depends Accurate Protein Synthesis Depends on Codon-Anticodon Recognitionon Codon-Anticodon Recognition
tRNA ChargingtRNA Charging
• A specific tRNA synthetase catalyzes A specific tRNA synthetase catalyzes the attachment of the appropriate the attachment of the appropriate amino acid to each tRNAamino acid to each tRNA
• Energy from conversion of ATP to AMP Energy from conversion of ATP to AMP drives the reactiondrives the reaction
Overview of Translation Overview of Translation
At the ribosome, codons in mRNA are At the ribosome, codons in mRNA are recognized by tRNA anticodons to place recognized by tRNA anticodons to place amino acids in the specific sequence amino acids in the specific sequence determined by the DNA.determined by the DNA.
Three Stages of Translation:Three Stages of Translation: Initiation- assemble components to start processInitiation- assemble components to start process Elongation- add amino acids in repeated cyclesElongation- add amino acids in repeated cycles Termination- release protein productTermination- release protein product
Initiation (Prokaryotic)Initiation (Prokaryotic)
Formation of initiation complex containing: Formation of initiation complex containing: Small ribosomal subunitSmall ribosomal subunit
mRNAmRNA
Initiator (f-Met) tRNAInitiator (f-Met) tRNA
Large ribosomal subunit Large ribosomal subunit
5’-------------AUGUUUCUCUGA---3’ mRNA
UAC
f-met
Elongation Elongation
a. next tRNA binds to mRNA at thea. next tRNA binds to mRNA at the A site A site
5’ -------------AUGUUUCUCUGA---3’ mRNA
UAC
f-met phe
AAA
P siteP site A siteA siteE siteE site
Elongation Elongation
b. amino acids are joined with b. amino acids are joined with peptidyl transferase peptidyl transferase
UAC
f-met phe
AAA 5’-------------AUGUUUCUCUGA---3’ mRNA
peptide bondpeptide bond
Elongation Elongation
c. ribosome moves by one codon (translocation)c. ribosome moves by one codon (translocation)--growing peptide is now in P site--growing peptide is now in P site--first tRNA is in E site--first tRNA is in E site
UAC
phe
AAA 5’-------------AUGUUUCUCUGA---3’ mRNA
f-met
Elongation Elongation
d. first tRNA is released from E sited. first tRNA is released from E site
UAC
AAA 5’-------------AUGUUUCUCUGA---3’ mRNA
phef-met
Elongation (second cycle)Elongation (second cycle)
a. next tRNA binds to mRNA at the a. next tRNA binds to mRNA at the A site A site
5’ -------------AUGUUUCUCUGA---3’ mRNA
UAC
AAA GAG
leuphef-met
Elongation (second cycle) Elongation (second cycle)
b. amino acids are joined with b. amino acids are joined with peptidyl transferase peptidyl transferase
5’ -------------AUGUUUCUCUGA---3’ mRNA
UAC
AAA GAG
leuphef-met
peptide bondpeptide bond
Elongation (second cycle) Elongation (second cycle)
c. ribosome moves by one codonc. ribosome moves by one codon--growing peptide is now in P site--growing peptide is now in P site--second tRNA is now in E site--second tRNA is now in E site
UAC
AAA 5’-------------AUGUUUCUCUGA---3’ mRNA
GAG
leuphef-met
Elongation (second cycle) Elongation (second cycle)
d. second tRNA is released from E sited. second tRNA is released from E site
UAC
AAA
5’-------------AUGUUUCUCUGA---3’ mRNA
GAG
leuphef-met
Termination Termination
a. release factor binds to stop codona. release factor binds to stop codon
UAC
AAA
5’-------------AUGUUUCUCUGA---3’ mRNA
GAG RF
leuphef-met
TerminationTermination b. protein chain is releasedb. protein chain is released other components separateother components separate
UAC f-met phe
AAA
GAG
leu
RF
5’-------------AUGUUUCUCUGA---3’ mRNA
Large Subunit
Small Subunit
Applying Your KnowledgeApplying Your Knowledge
If the mRNA sequence for codons 5, 6, and 7 of If the mRNA sequence for codons 5, 6, and 7 of a protein is 5’-AAG-AUU-GGA-3’, what is a protein is 5’-AAG-AUU-GGA-3’, what is the amino acid sequence in the protein? the amino acid sequence in the protein?
1.1. Gly-ile-lysGly-ile-lys
2.2. Arg-leu-gluArg-leu-glu
3.3. Glu-leu-argGlu-leu-arg
4.4. Asn-met-glyAsn-met-gly
5.5. Lys-ile-glyLys-ile-gly
Control of Initiation in ProkaryotesControl of Initiation in Prokaryotes
A.A. Small Ribosomal Subunit binds to mRNASmall Ribosomal Subunit binds to mRNAa.a. IF-3 binds to small ribosomal subunitIF-3 binds to small ribosomal subunitb.b. Small ribosomal subunit binds to Small ribosomal subunit binds to
Shine-Dalgarno sequence on mRNAShine-Dalgarno sequence on mRNA
A sequence in the 16S rRNA of the small ribosomal subunit
is complementary to the Shine-Dalgarno sequence on
mRNA
IF-3 = Initiation Factor 3
Control of Initiation in ProkaryotesControl of Initiation in Prokaryotes
B.B. Formyl-methionine tRNA binds to mRNAFormyl-methionine tRNA binds to mRNAa.a. IF-2 +GTP + f-met-tRNA joinIF-2 +GTP + f-met-tRNA joinb.b. f-met-tRNA binds to the first codonf-met-tRNA binds to the first codonc.c. IF-1 joins to small subunitIF-1 joins to small subunitd.d. IFs dissociate, GTP is hydrolyzed to GDPIFs dissociate, GTP is hydrolyzed to GDP
C.C. Large Ribosomal Subunit binds to mRNALarge Ribosomal Subunit binds to mRNA
Control of Initiation in EukaryotesControl of Initiation in EukaryotesBinding of Small Subunit assisted by proteins bound to Binding of Small Subunit assisted by proteins bound to -5’-methyl guanine cap-5’-methyl guanine cap -Poly-A tail -Poly-A tail
Control of Elongation by Elongation FactorsControl of Elongation by Elongation Factors
EF-Tu joins GTP and a charged tRNA to form a
complex that binds to the A site
EF-Ts regenerates the EF-Tu + GTP
complex
EF-G and GTP are required for ribosome
translocation
Control of Termination by Release FactorsControl of Termination by Release Factors
RF1 binds to UAA and UAG
RF2 binds to UAA and UGA
RF3 forms a
complex with GTP that binds to the
ribosome
Energetics of TranslationEnergetics of Translation
Number of Phosphate Bonds Number of Phosphate Bonds Required (use of ATP or GTP)Required (use of ATP or GTP)
InitiationInitiation 1 for assembly of ribosomal 1 for assembly of ribosomal subunitssubunits
2 for activation of f-met tRNA2 for activation of f-met tRNA
ElongationElongation 2 for activation of each tRNA2 for activation of each tRNA
2 for addition of each amino acid2 for addition of each amino acid
TerminationTermination 1 for dissociation of ribosomal 1 for dissociation of ribosomal subunitssubunits
Energetics of TranslationEnergetics of Translation
How many phosphate bonds are required to How many phosphate bonds are required to build a protein of 100 amino acids?build a protein of 100 amino acids?
First Amino AcidFirst Amino Acid 33
Next 99 Amino Next 99 Amino AcidsAcids
99x4=39699x4=396
TerminationTermination 11
Total Total 400400