BCHM 4116 1st Edition Lecture 31 Outline of Last Lecture 1 Rules in Condon Anticodon Pairing 2 Ribosomes 3 Translation Outline of Current Lecture 1 Elongation 2 Termination 3 Translation in Eukaryotes Current Lecture Chapter 30 Protein Synthesis Cont a Elongation i Synthesis of all peptide bonds from 1st to last ii 50S subunit catalyzes peptide bond formation iii A acceptor site attachment site for incoming aminoacyl tRNA iv P peptidyl site occupied peptidyl tRNA v E exit site occupied by unloaded or deacylated tRNA which has lost its peptidyl chain through peptidyl transferase reaction vi Requirements 1 mRNA 70S ribosome peptidyl tRNA complex 2 aminoacyl tRNA 3 set of proteins elongation factors 4 GTP vii Elongation factors 1 EF Tu a G protein that binds aminoacyl tRNA deliveirs it to A site b Hydrolyzes GTP to GDP once base pairing b w codon anticodon is established at A site 2 EF Ts a Guanine nucleotide exchange factor GEF that replaces GDP on EF Tu w GTP b Recycles EF Tu 3 EF G a G protein that promotes translocation of mRNA viii Peptidyl Transfer 1 Aka transpeptidatoin 2 Central reaction of protein synthesis 3 Actual peptide bond forming step These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 4 No energy input required b Termination i Triggered when ribosome reaches stop codon on mRNA ii Polypeptide chain is released iii Ribosomal subunits dissociate from mRNA iv Stop codons recognized by release factors RF 1 RF promote polypeptide release from ribosome a RF 1 i Recognizes UAA UAG b RF 2 i Recognizes UAA UGA 2 Translation in Eukaryotes a Eukaryotic initiation factors eIFs i Stage 1 43S preinitiation complex 1 eIF1 eIF1A eIF3 eIF5 binds to 40S a eIF1 eIF1A binds to create conformational change in 40S b eIF3 binds to solvent exposed in 40S i eIF3 serves as a platform and scaffold for recrument of mRNA dipper ii Stage 2 48S initiation complex 1 Binds 43S preinitiation complex to mRNA 2 Migrates 40S ribosomal subunit to correct AUG 3 Requires eIF4 group poly A binding protein PABP a These recognizes 5 terminal cap 3 terminal poly A tail of mRNA unwind 2ndary structure b eIF4 eiF4B eIF4F eiF4A eIF4E eiF4G i 4F 1 trimeric complex with 4A 2 binds to cap to initiate association w 4B formation of 48S ii 4A 1 ATP dependent RNA helicase iii 4E 1 binds 5 terminal methyl GTP 2 mRNA cap binding protein of 4F 3 key regulatory element iv 4G 1 interacts PABP 2 bridge b w cap binding 4E v F1 F1A 1 Necessary to open mRNA 4 5 cap 3 poly A tail of mRNA binding to 4G brings 2 ends of mRNA together closing the circle a ensure that only appropriately processed transcript are translated b helps to protect the mRNA from exonucleolytic degradation iii Stage 3 80S initiation complex 1 48S stops at AUG GTP hydrolysis causes ejection of initiation factors bound to 40S 2 F5 in conjunction w 5B stimulates GTPase activity of F2 3 Ejection of eiFs is followed by 60S to form 80S whereupon translation begins 4 eIF2 GDP is recycled to eIF2 GTP by eIF2B