Topic 4B - Protein Transport Across Membranes Flashcards
T of F mitochondria have their own DNA and ribosomes?
true
are more proteins in mitochondria from nuclear genome or mitochondrial?
nuclear (1000) vs mitochondrial (13)
does mitochondria have post-translational translocation or co-transloational?
post-translational
what kinds of proteins is TIM22 specialized for the insertion of?
multipass proteins!
is transport in mitochondria active or passive?
active
what does the oxidative phosphorylation generating electrochemical proton gradient do?
helps pull proteins across inner membrane (since N terminal is positive it is attracted negative charge)
also helps with ATP synthesis –> important for stripping chaperone proteins in cytosol
what helps pull protein through TOM?
MIA complex
what chaperones and complexes help with the insertion of proteins into the mitochondrial matrix?
cytosolic hsp70
TOM and TIM23
mitochondrial hsp70
hsp60 (if improperly folded)
what complexes help with the insertion of proteins into the outer mitochondrial membrane
TOM and SAM!!!
- SAM inserts proteins as beta-barrels
what complex is used for inserting bacterial beta barrels?
BAM! structurally related to SAM
what is the difference between transmembrane mitochondrial proteins and other mitochondrial proteins?
transmembrane proteins have both internal sequence and N terminal sequence
where are transmembrane proteins inserted in the mitochondria?
into the inner membrane
what happens to proteins with a second hydrophobic sequence?
they are inserted released laterally in the intermembrane space after TIM23 recognizes hydrophobic sequence and N terminal sequence is cleaved (hydrophobic anchor in inner membrane)
or
pass through TIM23 and grabbed by OXA –> protein ends up anchored in inner membrane (like other one)
or or
the hydrophobic sequence could also be cleaved and the protein released as a true inner membrane protein
what is different between mitochondrial transport and chloroplast transport?
TOC and TIC instead of TOM and TIM
no electrochemical gradient at inner membrane (GTP and ATP used)
has extra membrane – > thylakoid space
what are the major functions of the ER?
glycosylation
intracellular Ca storage
and then also
lipid biosynthesis for most organelles
production of transmembrane proteins
how can we isolate ER
centrifugation
then sediment through gradient of sucrose
- smooth sediments in low sucrose concentration
- rough in high
does ER have more co-translational or post-translational translocation?
co-translational
what determines co-translational vs post-translational translocation?
N terminal sequence
what is the SRP? what is its receptor?
signal recognition particle
binds to signal-sequence binding pocket and ribosome which pauses translation
receptor = SRP receptor
- recognizes SRP-protein complex and binds
what are the two gates of the translocator protein in the ER used for?
pore for hydrophillic protein portions (regular part)
opens laterally for hydrophobic parts (stop sequence)
is specificity of signal important for translocator protein in ER?
no it just recognizes hydrophobic sequences
what kind of transport is Get1-Get2 receptor involved with?
post-translational translocation in the ER
for integration of C tail-anchored proteins
what does Get3 do?
brings C tail-anchored proteins to Get1-Get2 receptor which binds to C terminal sequence
Get3 then hydrolyzes ATP and releases protein
why are glycosylated proteins considered N-linked?
because they are glycosylated on target asparagine (N) amino side chains
how does glycosylation play a role in protein folding?
- calnexin binds to terminal glucose on oligosaccharides of incompletely folded proteins
- glucosidase removes the terminal glucose, releasing protein from calnexin
glucosyl transferase checks to see if protein is properly folded - if it is, protein is free, if not, glucosyl transferase adds another glucose, renewing protein’s affinity for calnexin
what is the difference between calnexin and calreticulin
calreticulin is soluble
calnexin is membrane bound
both bind improperly folded proteins so glucosidase can cleave the terminal glucose
when does manose get cleaved?
after a certain number of cycles, manose will be cleaved by glucosidase and then the protein will be degraded via the retrotranslocation pathway
what does glucosidase do?
cleaves the terminal glucose from improperly folded proteins in ER
what does glucosyl transferase do?
checks to see if proteins are properly folded. will add glucose to proteins that are improperly folded to renew their affinity for calnexin or calreticulin
how does the retrotranslocation pathway work?
chaperones keep misfolded proteins from becoming more folded
lectin recognizes proteins with cleaved manose and binds as well as disulfide isomerase
misfolded proteins are targeted to a translocator complex in the ER membrane and then sent to cytosol
they are ubiquitylated and de-glycosylated by glycanase then degraded in proteasomes
what does lectin do?
recognizes proteins with cleaved manose as part of the retrotranslocation pathway
what does disulfide isomerase do in the retrotranslocation pathway
breaks down secondary structures of proteins
what does glycanase do in the retrotranslocation pathway?
deglycosylates proteins
which ER pathway do viruses modify to degrade proteins that would usually fight the virus
retrotranslocation pathway
what is the unfolded protein response?
misfolded proteins activate a transmembrane kinase
things happen and eventually transcription regulator is created and enters the nucleus through NPC to activate genes that encode ER chaps
the chaps are then made in ER to help with folding
