7- Translation And Post Teanslational Modifications Flashcards
How does a ribose e start translating mRNA
It scans from the 5’ cap of the mRNA. Translation starts from the first AUG and continues in frame
How do ribosomes differ in eukaryotes and prokaryotes
Eukaryotes have 80S ribosomes, with two subunits, one more dense than the other, one being 40S and the other being 60S
Prokaryotes have 70S ribosomes, with two subunits, one more dense than the other, one being 30S and the other being 50S
What do Aminoacyl tRNA synthetases do
forming the aminoacyl tRNA complex. There is one of each amino acid
Describe the initiation step of translation
Dissociation of ribosome subunits
Assembly of pre initiation complex (Met tRNA + initiation factors (eIFs) + 40S subunit)
Binding of mRNA to pre initiation complex at AUG
Binding of 60s and GTP hydrolysed to GDP
Describe the elongation step in translation
A new tRNA carrying the second amino acid to the A (aminoacyl) site
The peptide bond is formed between the two amino acids by peptidyl transferase on the 60S subunit
The second tRNA is translocated to the P (peptidyl) site and the first tRNA is dissociated Elongation factors are proteins that promote the movement of the ribosome along mRNA using GTP
There is a new cycle with a new step 1, repeated, until a stop codon is encountered
Give some post translational modifications
Disulphidebondformatione.g.insulin
o Proteolyticcleavagee.g.insulin–AandBchains
o Additionofcarbohydratese.g.glycosylation
o Additionofphosphatese.g.phosphorylation
o Additionoflipidgroupse.g.prenylation,acylation
o Hydroxylatione.g.collagen(seeLeitingerlectureoncollagen)
Describe the termination step in translation
The recognition of a stop codon by release factors, which are proteins, NOT tRNA, bind to the A site containing the stop codon. Out of frame stop codons are not recognised
The release of the peptide chain via peptidyl transferase that catalyses the transfer of the completed protein chain to water and releases it from the ribosome
The dissociation of release factors and ribosomes
Describe how proteins are synthesised in the Rer
Secretory and transmembrane proteins are synthesised in the rough endoplasmic reticulum
The ribosomes on the rER have a signal sequence in the first 20 24 amino acids. They are a sequence of hydrophobic amino acids to direct these proteins to the endoplasmic reticulum
The signal sequence is recognised by a protein RNA complex a signal recognition particle (SRP).
This halts translation
The SRP binds to a receptor on the rER surface, and translation can resume
The protein is synthesised as above, and the newly synthesised protein is pulled in via a pore into the lumen of the endoplasmic reticulum
Transmembrane proteins have a hydrophobic sequence that holds them in the membrane
The signal sequence is cleaves by a signal peptidase and the folding occurs
Give examples of antibiotics inhibiting protein synthesis
Streptomycin Tetracycline Erythromycin Chloramphenicol Puromycin Inhibits initiation Inhibits aminoacyl tRNA binding Inhibits translocation Inhibits peptidyl transferase Terminated elongation prematurely
What is the 5’ cap made from
7 methyl guanosine
Where is the amino acid attached to on the tRNA and how
The 3’ end by a aminoacyl tRNA synthesase
