Lecture 11 Flashcards
what are the 2 types of tRNAmet that E. Coli has?
tRNAfmet - met residues attached are formylated
tRNAmmet - met residues attached not formylated
what does IF-3 do
22kDa.
binds 30S subunit, prevents association with 50S subunit
IF-1
9kDa
binds near the A site directs tRNAfmet to the P site
IF-2
120kDa
reacts with tRNAfmet and GTP to form a ternary complex
Delivers ternary complex and mRNA to the partial P site in the 30S subunit mRNA complex
triggers GTP hydrolysis when the 50S subunit joins the complex. Does not recognise met-tRNA or any aa tRNA used for elongation
eIF-4F
cap binding complex in eukaryotes
made of eIF-4E, 4G and 4A
how is protein synthesis regulated during the cell cycle
during G2 to M transition there is a reduction in the overall rate of the protein sythesis
due to the cell cycle dependent dephosphorylation of eIF-4E (cap binding). this lowers the affinity of ribosomes for the cap
picornaviruses
uses IRES
on infection a protease cleaves eIF-4G thereby rendering it unable to bind to eIF-4E the cap binding complex. This prevents binding and scanning ribosomes and therefore shuts off 90% of host synthesis allowing for maximum competition with the host
3 steps of elongation
- codon directed binding of the incoming aa-tRNAs
- peptide bond formation
- translocation of ribosome along the mRNA in a 5’ to 3’ direction by length of one codon
RF-1
release factor
recognises UAA and UGA
RF-2
release factor
recognises UAA and UAG
RF-2
GTP binding protein
stimulates binding of RF-1 and RF-2
name the 5 translational control methanisms
- regulation of the activities of IFs/EFs by phosphorylation e.g heme in reticulocytes
- autogenous regulation e.g. ribosomal protein synthesis in E. Coli
- blocking.opening of ribosome binding sites by reversible changes in secondary structure
- reversible binding of a repressor protein to a response element in 5’ UTR e.g. iron homeostasis in mammals
- differential stability of mRNA
