Initial amino acid in prokaryotic protein synthesis -
Ans. is 'c- i.e., Formyl-methionine o in prokaryotes and in mitochondria, the first amino acid methionine is modified by formylation, i.e. the initiator t-RNA carries an N-formylated methionine. The formyl group is added by the enzyme transformylase (formyl- transferase). In Eukaryotes, the initiator t-RNA carries a methionine that is not formylatedDifferenceProkaryotesEukaryotesm-RNAPolycistronic i.e. have several coding regions; each with its initiation & termination codon producing a seperate polypeptideMonocistr onic with one coding regionAmino acid incorporation rate18 aa/sec6aa/sec.Initial amino acidFormylated methionine ( f-met)Methionine r (Met)Initial t-RNAt-RNA/MettRNAMetTranscription & translationTranslation starts before transcription is ended (coupled)UncoupledInitiation factors (IF)3i.e.IF1,IF2,IF3> 10 designated elFDetermination of initiatingcodon# Shine Dalgarno sequencer# Facilitated by IF-2 bound to GTPKozak consensus sequencesr Facilitated by elF-2 bound to GTP (Plus additional elF)Elongation: Del Every of aminoacyl t-RNA to A site# Facilitated by EF-Tu & EF-TsFacilitated by EF1 a and EF 1 b yNucleotide exchange factors# EF - Ts (as it exchanges its GTP for GDP on EFTu)EF 1 b g (as it exchanges its GTP forGDP on EF a)Peptidyi transferase activity catalyzing peptide bond formation23 S rRNA of 50 S ribosomal subunit (ribozyme)28 S rRNA of 60 S ribosornal subunit (ribozyme)TranslocationRequires EF-G & GTPRequires EF-2 & GTPTerminationRelease factor (RF) 1 recognizes UAA & UAG, RF2 recognizes UAA & UGARF-3 (bound to GTP) causes release ofRF-1 or RF-2 as GTP is hydrolysedeRF recognizesail 3 UAA, UAGandUGA and release nascent polypeptide chaineRF-3 (bound to GTP) function like prokaryotic RF-3 & release eRF
Arginine
Methionine
Formyl-methionine
Alanine
Amino Acids Basics