Protein synthesis Flashcards
What is Riacin and what does it do
N-glycosidase
-inactivates large eukaryotic ribosome
What are the functions of the ribosome
- binds mRNA so codons can be read
- BInding sites for tRNA
- mediate the interaction of non-ribosomal protein factors promoting: polypeptide chain initiation, polypeptide chain elongation and polypeptide chain termination
- catalyse peptide bond formation
What does the movement of ribosome allow
Translation of sequential codons
Where are prokaryotic ribosomal proteins found
Located on subunit back and sides
IN prokaryotes, what are the names of the tRNA binding sites
- A site
- P site
- E site
What is the A site on a prokaryotic ribosome
Accommodates incoming amino-acyl-tRnA
Wat is the P site on prokaryotic ribosome
Accommodates the tRNA attached to growing peptide chain
What is the E site on prokaryotic ribosome
Accommodates the tRNA without amino acid, that is leaving
How do tRNA’s bind to eukaryotic ribosomes
all 3 tRNA have anticodons bound to 30s subunit and the rest of the tRNA bound to 50s subunit
What do the tRNA on the A site and P site interact with the mRNA via
Base-pairing
What is elongation in translation
- links growing polypeptide to incoming tRNA amino acid
- Growing polypeptide transferred from peptide-tRNA in the p site to the incoming amino acid tRNA in A site
- new peptidyl-tRNA is transferred from A to P site
- Uncharged tRNA moves to E site
what is polycistronic
When prokaryotic mRNA has more than one coding region and each coding region has its own initiation and termination codons
What is monocistronic
mRNA has just one coding region
What is polysome
multiple ribosomes can translate a message because of length of mRNA
What is initiation and what happens in it
involves assembly of translation system components
- mRNa
- 2 ribosomal subunits
- amino acyl-tRNA specified by the 1st codon
- GTP
- Initiation factors
What do ribosomes recognize the start codon via
Shine-Delgarno sequence (not in eukaryotes)
What are the stages of initiation
- ribosomes recognize start codon (only in prokaryotes)
- initiation and binding of tRNA in P site
- HYdrolysis of GTP and initiation factors are released
- allows large subunits to bind
What happens in elongation
- Involves addition of amino acid to carboxyl end of growing chain
- Delivery of the next amino-acyl tRNA by elongation factors which requires GTP hydrolysis
- Ribosome them advances 3 nucleotides to mRNA 3’ end (translocation)
What happens in termination
- termination codons recognized by release factors
- Allow GTP to hydrolase and release of protein because RF binding causes hydrolysis pf bond linking peptide to tRnA on p-site and so protein is released
What do antibiotics do
Block translation
What does a low level of streptomycin mean
Ribosome misreads mRNA
What does a high level of streptomycin mean
Prevents chain initiation (causes cell death)
What does chloramphenicol do
Binds near A site and stops peptide formation. HOWever its toxic because it affects mitochondrial translation
What does tetracycline do
- Bind to small subunit or prokaryotic ribosomes and prevents entry of amino acyl-tRNA into A site
- Stops synthesis and is an energy drain
- However allow elongation factors to bind
What folds proteins
Chaperones
What is phsphorylation reversedby
PHosphatases
what is phosphorylation catalysed by
kinases
How are proteins directed to their ultimate destinations
Small ubiquitin related modifier addition can signal cellular localisation
HOW are many transmembrane and secretory proteins translocated through membranes via
Secretory pathway through ER
- as N terminal signal sequences emerge from ribosome, associate with signal recognition particle
- Docks with ER receptor
- PRotein synthesis takes place and pushes the protein into the ER
- Post translational modification occurs
