Nucleocytoplasmic Transport Flashcards
(14 cards)
what does the nuclear envelope do?
separate cytoplasm and nucleus
structure of nuclear envelope?
freeze fractured paramecium nucleus with studded nuclear pore complex
made up of subunits
supported by nuclear laminas - filaments/NPC
how are lamins anchored?
interaction with membrane protein
lipid modification and insertions
what are mutations in lamin A associated with?
Hutchinson-Gilford Progeria syndrome
an inherited premature ageing condition
how are molecules transported through nuclear pore complexes?
ions/glucose - import/export
virus capsid - import
protein/RNA - export
ATP/Protein - shuttled
whats special about transport through nuclear pore?
works both ways but has different rates of transport
What’s important about Ran?
a related nuclear protein bound to GTP or GDP
it controls the direction of nuclear transport via carefully maintained gradient
how are proteins exported?
cargo in the nucleus binds as a trio to RanGTP and exportin which then all moves through the nuclear pore complex
RanGAP enzyme removes the phosphate from RanGTP and so it can no longer bind and the whole complex falls apart
exportin goes back through pore
how are proteins imported?
cargo binds to importin which is complementary and passes through the pore
regulated in nucleus when RanGTP recognises importin and binds to the complex - a conformational change which results in the cargo no longer being able to bind
importin-RanGTP complex passes through pore where RanGAP interacts with and the enzyme removes phosphate - complex breaks up
how does faciliated diffusion work?
cargo at outer membrane imports karyopherin which has binding sites for FG repeats
diffuses around until it bumps into a nuclear pore complex and binds to a hydrogen bond, continues to hang around for longer to increase chances of interacting with more FG repeats
what do RNAs exist as?
ribonucleoprotein complexes
whats special about U-snRNA splicing factors?
they have a weird loop where head out of nucleus and protein added which is then incorporated back into the nucleus
what is Dbp5?
an RNA helicase which aids in translocation of correctly processed mRNA through the NPC
what does Dbp5 do?
untwist secondary structures
as diffuses towards pore forms transient interactions and twists the RNA so it can move through the pore
