Translation How the Genetic Information Is Used to Build a Protein

DNA Information Flow From DNA initial transcript RNA transcription Protein translation replication processing mature RNA

Properties of the Genetic Code TripletTriplet –3 nucleotides code for 1 amino acid Non-overlappingNon-overlapping –Codons are adjacent to each other DegenerateDegenerate –Some amino acids have more than one codon “Almost” universal“Almost” universal –A few exceptions occur in mitochondrial, bacterial and protist genes

5’  3’ Sequence of CODONS

Accurate Protein Synthesis Depends on Codon-Anticodon Recognition

tRNA Charging A specific tRNA synthetase catalyzes the attachment of the appropriate amino acid to each tRNA A specific tRNA synthetase catalyzes the attachment of the appropriate amino acid to each tRNA Energy from conversion of ATP to AMP drives the reactionEnergy from conversion of ATP to AMP drives the reaction

Overview of Translation At the ribosome, codons in mRNA are recognized by tRNA anticodons to place amino acids in the specific sequence determined by the DNA. Three Stages of Translation: Initiation- assemble components to start process Initiation- assemble components to start process Elongation- add amino acids in repeated cycles Elongation- add amino acids in repeated cycles Termination- release protein product Termination- release protein product

Initiation (Prokaryotic) Formation of initiation complex containing: Small ribosomal subunit mRNA mRNA Initiator (f-Met) tRNA Initiator (f-Met) tRNA Large ribosomal subunit Large ribosomal subunit 5’ AUGUUUCUCUGA---3’ mRNA UAC f-met

Elongation a. next tRNA binds to mRNA at the A site a. next tRNA binds to mRNA at the A site 5’ AUGUUUCUCUGA---3’ mRNA UAC f-met phe AAA P site A site E site

Elongation b. amino acids are joined with peptidyl transferase b. amino acids are joined with peptidyl transferase UAC f-met phe AAA 5’ AUGUUUCUCUGA---3’ mRNA peptide bond

Elongation c. ribosome moves by one codon (translocation) c. ribosome moves by one codon (translocation) --growing peptide is now in P site --first tRNA is in E site UAC phe AAA 5’ AUGUUUCUCUGA---3’ mRNA f-met

Elongation d. first tRNA is released from E site d. first tRNA is released from E site UAC AAA 5’ AUGUUUCUCUGA---3’ mRNA phe f-met

Elongation (second cycle) a. next tRNA binds to mRNA at the A site a. next tRNA binds to mRNA at the A site 5’ AUGUUUCUCUGA---3’ mRNA UAC AAAGAG leuphe f-met

Elongation (second cycle) b. amino acids are joined with peptidyl transferase b. amino acids are joined with peptidyl transferase 5’ AUGUUUCUCUGA---3’ mRNA UAC AAA GAG leu phe f-met peptide bond

Elongation (second cycle) c. ribosome moves by one codon --growing peptide is now in P site --second tRNA is now in E site c. ribosome moves by one codon --growing peptide is now in P site --second tRNA is now in E site UAC AAA 5’ AUGUUUCUCUGA---3’ mRNA GAG leu phe f-met

Elongation (second cycle) d. second tRNA is released from E site d. second tRNA is released from E site UAC AAA 5’ AUGUUUCUCUGA---3’ mRNA GAG leu phe f-met

Termination a. release factor binds to stop codon a. release factor binds to stop codon UAC AAA 5’ AUGUUUCUCUGA---3’ mRNA GAG RF leu phe f-met

Termination b. protein chain is released b. protein chain is released other components separate other components separate UAC f-met phe AAA GAG leu RF 5’ AUGUUUCUCUGA---3’ mRNA Large Subunit Small Subunit

Applying Your Knowledge If the mRNA sequence for codons 5, 6, and 7 of a protein is 5’-AAG-AUU-GGA-3’, what is the amino acid sequence in the protein? 1.Gly-ile-lys 2.Arg-leu-glu 3.Glu-leu-arg 4.Asn-met-gly 5.Lys-ile-gly

Control of Initiation in Prokaryotes A.Small Ribosomal Subunit binds to mRNA a.IF-3 binds to small ribosomal subunit b.Small ribosomal subunit binds to Shine-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 Prokaryotes B.Formyl-methionine tRNA binds to mRNA a.IF-2 +GTP + f-met-tRNA join b.f-met-tRNA binds to the first codon c.IF-1 joins to small subunit d.IFs dissociate, GTP is hydrolyzed to GDP C.Large Ribosomal Subunit binds to mRNA

Control of Initiation in Eukaryotes Binding of Small Subunit assisted by proteins bound to -5’-methyl guanine cap -Poly-A tail -5’-methyl guanine cap -Poly-A tail

Control 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 Factors RF 1 binds to UAA and UAG RF 2 binds to UAA and UGA RF 3 forms a complex with GTP that binds to the ribosome

Energetics of Translation Number of Phosphate Bonds Required (use of ATP or GTP) Initiation 1 for assembly of ribosomal subunits 2 for activation of f-met tRNA Elongation 2 for activation of each tRNA 2 for addition of each amino acid Termination 1 for dissociation of ribosomal subunits

Energetics of Translation How many phosphate bonds are required to build a protein of 100 amino acids? First Amino Acid 3 Next 99 Amino Acids 99x4=396 Termination1 Total400