Lecture 5 Flashcards
What causes a polypeptide to be sent to the ER?
Detection of a signal sequence by SRP (signal recognizing protein)
What type of translation is used in insert of polypeptides to the ER?
Co-translational transport
What is the signal sequence used to target proteins to the ER?
A large hydrophobic region at the N terminus
What is the receptor for ER targeted proteins once they have bound SRP?
The alpha domain of the SRP receptor
What is the translocon for ER targeted proteins?
Sec 61-Alpha
What happens to the signal sequence of an ER targeted protein?
It is cleaved by a signal peptidase
What molecular chaperone pulls the ER targeted protein into the lumen and prevents misfolding?
BiP
What is the energy source for ER targeted proteins?
GTP
What is the energy source of the BiP protien?
ATP
When does insertion of a mitchondrial protein occur?
Once the protein has already been fully transcribed BUT has not folded
What prevents mitochondrial proteins from folding before they are inserted?
HSC70
What is the signal sequence for mitochondrial targeting?
A 20-50 residue long amphipathic alpha helix at the N terminal
What are the receptors for mitochondrial targeted proteins?
TOM 20/22 for the outer membrane, TIM 44 for the inner membrane
What is the translocon for the outer membrane of the mitochondria?
TOM 40
What is the translocon for the inner membrane of the mitochondria?
TIM 23/17
Which region of the mitochondria do matrix targeted proteins enter from the cytosol?
At contact sites where the two membranse of the mitochondria almost touch
What happens to the signalling sequence for mitochondrial matrix proteins?
It is cleaved by a matrix processing protease?
What happens to the sequence for the intermembrane space?
It is cleaved by a protease in the intermembrane space
Where does the energy for import of mitochondrial proteins come from?
ATP hydrolysis by chaperone proteins and H+ gradient for transport across the intermembrane space
What is the difference in transport between an intermembrane protein and matrix protein?
A matrix protein is ‘pulled’ across the inner membrane by matrix HSC70, intermembrane proteins enter the TIM 23/17 translocon, then stop moving across due to the signal sequence, moving out of the translocon where a inter-membrane protease removes the rest of the coding sequence by cleaving the polypeptide at the level of the inner membrane
What is a peroxisome?
A cell organelle which contains oxidative enzymes useful for the dgradation of fatty acids
What is the signal for peroxisome targeted proteins?
Ser-Lys-Leu (SKL Sequence) at the C terminal of the protein
What recognises the signal sequence for peroxisome targeted proteins?
Pex 5 recognises the protein in the cytosol which then binds to Pex14 on the perioxisome membrane
Where does the peroxisome targeted protein and pex 5 dissociate?
Once they have both entered the perioxisome
What is the translocon complex for protine insertion into peroxisomes?
A complex of pex 2, 10, 12
Where does the energy for import of polypeptides into peroxisomes come from?
ATP
What happens to the signal sequence for peroxisome targeted proteins?
It becomes incorporated into the protein sequence
What is the signal sequence for nuclear targeted proteins?
Nuclear Localisation sequence at the N terminal, usually rich in lysine and argnine
What state are proteins transported into the nucleus in?
Fully folded functional proteins
What recognises the nuclear localisation sequence?
Importin
What protein enables the importin-nuclear targeted protein to move across the nuclear pore?
Ran-GDP
What happens to the the Ran-GDP protein inside the nucleus?
GTPase exchange factor exchanges its bound GDP for a GTP allowing it to bind to the importin and ferry it to the cytoplasm via the nuclear pore
What is the energy source for nuclear targeted protein transport?
None (other than the GTP required to bring the importin back out into the cytoplasm
Identify the transport Proteins
What type of membrane protein is this?
What type of membrane protein is this?
What type of membrane protein is this?
What type of membrane protein is this?
