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

5’3’ Sequence of CODONS

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


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


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


f-met


d. first tRNA is released from E sited. first tRNA is released from E site

UAC


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


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


UAC

AAA GAG

leuphef-met

peptide bondpeptide bond


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


GAG

leuphef-met


d. second tRNA is released from E sited. second tRNA is released from E site

UAC

AAA


GAG

leuphef-met

Termination Termination

a. release factor binds to stop codona. release factor binds to stop codon

UAC

AAA


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


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

translation how the genetic information is used to build a protein

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