BCHM 4116 1st Edition Lecture 31Outline of Last Lecture1. Rules in Condon-Anticodon Pairing2. Ribosomes 3. Translation Outline of Current Lecture 1. Elongation2. Termination 3. Translation in Eukaryotes Current LectureChapter 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-tRNAiv. P – peptidyl site – occupied peptidyl tRNAv. E – exit site – occupied by “unloaded” or deacylated tRNA which has lost its peptidyl chain through peptidyl transferase reaction vi. Requirements1. mRNA: 70S ribosome: peptidyl tRNA complex2. aminoacyl-tRNA3. set of proteins – elongation factors4. GTPvii. Elongation factors1. EF-Tua. G protein that binds aminoacyl-tRNA & deliveirs it to A siteb. Hydrolyzes GTP to GDP once base pairing b/w codon & anticodon is established at A site 2. EF-Tsa. Guanine-nucleotide exchange factor (GEF) that replaces GDP on EF-Tu w/ GTPb. Recycles EF-Tu 3. EF-Ga. G protein that promotes translocation of mRNA viii. Peptidyl Transfer1. Aka transpeptidatoin2. Central reaction of protein synthesis3. Actual peptide bond forming stepThese 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 requiredb. Termination i. Triggered when ribosome reaches “stop” codon on mRNA ii. Polypeptide chain is releasediii. Ribosomal subunits dissociate from mRNAiv. Stop codons recognized by release factors (RF)1. RF – promote polypeptide release from ribosomea. RF-1 i. Recognizes UAA UAGb. RF-2i. Recognizes UAA UGA 2. Translation in Eukaryotesa. Eukaryotic initiation factors (eIFs) i. Stage 1 – 43S preinitiation complex1. eIF1, eIF1A, eIF3, eIF5 binds to 40S a. eIF1 & eIF1A binds to create conformational change in 40Sb. eIF3 binds to solvent-exposed in 40Si. eIF3 serves as a platform and scaffold for recrument of mRNA dipper ii. Stage 2 – 48S initiation complex1. Binds 43S preinitiation complex to mRNA 2. Migrates 40S ribosomal subunit to correct AUG3. Requires eIF4 group & (poly)A-binding protein (PABP)a. These recognizes 5’-terminal cap & 3’-terminal poly(A) tail of mRNA, unwind 2ndary structureb. eIF4 = eiF4B & eIF4F, eiF4A, eIF4E, eiF4Gi. 4F1. trimeric complex with 4A2. binds to cap to initiate association w/ 4B & formation of 48S ii. 4A1. ATP-dependent RNA helicaseiii. 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 & F1A1. Necessary to open mRNA4. 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 translatedb. helps to protect the mRNA from exonucleolytic degradationiii. Stage 3 – 80S initiation complex1. 48S stops at AUG, GTP hydrolysis causes ejection of initiation factors bound to 40S 2. F5, in conjunction w/ 5B stimulates GTPase activity of F23. Ejection of eiFs is followed by 60S to form 80S, whereupon translation begins 4. eIF2: GDP is recycled to eIF2:GTP by