L 21 Flashcards
(27 cards)
What are the three tRNA binding sites in a ribosome?
Aminoacyl-tRNA
Peptidyl tRNA
Exit
What does the A site do?
tRNA selection
What does the P Site do?
does peptidyl transfer
What does the E site do?
Allow uncharged tRNA to exit
Where is the polypeptide chain transferred on to?
it is transferred onto the incoming aa tRNA
What catalyzes the A site?
aa-tRNA: EF-Tu: GTP
GTP binds to EF Tu and gets tRNA selection to work
What catalyzes the P Site?
the ribosome large subunit.
Ribosome catalyze itself
Release of the polypeptide occurs in which site?
In the P site.
how does the release factor work?
it recognizes the stop codon and transfers the polypeptide to the water
What is the first major step of termination?
RF recognizes stop codon
What is the second major step of termination?
peptidyl transferase transfers the polypeptide to H2O
What is the third major step of termination?
translocation mediated by ribosome recyling factor and EF F: GTP
ribosomal subunits dissociate, ready for reinitiation
What does RRF stand for?
Ribosome recyling factor
How does EF-G cooperate with release factors during termination?
It works to disassemble spent tRNAs, subunits, mRNA
how much energy is in a peptide bond?
4 High Energy Phosphate per Peptide Bond
Free NRG released is 122 kj/mol
Free NRG of peptide bond 21 kj/mol
Net free NRG change -100kj/mol
How do proteins exit after they’ve been made?
N terminus of growing polypeptide worms through an exit in the large subunit?
Since preprotein translocase is an integral membrane protein, it will require what for correct insertion into the ER membrane?
requires other molecules of preprotein translocase for its correct insertion
What is a preprotein translocase?
a protein conducting channel with an aqueous pore that span the ER membrane
What are N terminal hydrophobic signal sequences like?
has a positive charge and hydrophobic stretch of about a dozen residues.
What does the N terminal hydrophobic signal sequence do?
direct secreted and membrane proteins in the translocase
What is SRP?
Signal Recognition Particle
What are the three functions of SRP?
- Recognize signal sequence emergying from ribosome tunnel
- Pause translation
- Direct ribosome and nascent polypeptide to preprotein translocase channel on endroplasmic reticulum membrane
Like ribosomes and spliceosome, the SRP and Sr are what?
ribonucleoproteins
What is SR?
SRP receptor
