Protein Synthesis Initiation Complex

mRNA, tRNA, ribosomes

start codon

AUG -- met

stop codons

UAA, UAG, UGA

what direction is mRNA written and translated

what direction are proteins written and synthesized in

mRNA 5'-->3'

proteins N term-->C term

Wobble effect

ability of an anticodon to pair with more than one codon

ex: 1 tRNA for Ala recognizes all 4 Ala codons: GCA, GCC, GCG, GCU

I nucleotide

inosine

sometimes present in anticodons

makes anticodon less specific, permits less stringent base pairing

can pair with any pair except G (start/stop codons end in G)

aminoacyl-tRNA synthetase

activates aa with ATP, forming aminoacyl grp

transfers trp to tRNA (aminoacylation)

at least one aminoacyl-tRNA synthetase for each of 20 aa

proofreading ability, avoid binding wrong aa

initiator tRNA

methionyl tRNA

Shine-Dalgarno sequence

PROKARYOTES

non-translate seq, assists with alignment of mRNA with small ribo subunit

Kozak Sequence

EU equiv of Shine-Dalgarno sequence

(helps mRNA align with small ribo subunit)

3 sites in ribosome

P peptidyl site

A aminoacyl site

E elongation site

peptidyltransferase

transfers initiating methionine residue and then continues elongation

Streptomycin

prevents binding of fmet-tRNA to small subunit of PRO ribo, interferes w protein synth and causes codon misreading

mutations in proteins assoc w small subunit can confer resistance or even dependence

tetracyclines

inhibit binding of aminoacyl-tRNAs to mRNA-ribosome complex

puromycin

analog of aminoacyl-tRNA, binds to A site, halting elongation

works in PRO and EU

Erythromycin

inhibits peptidyl transferase in PRO

Cyclohexamide

inhibits peptidyl transferase in EU

Ricin

castor bean toxin

attacks rRNA by removing adenine-->inactivation