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The flashcards below were created by user
jaz584
on FreezingBlue Flashcards.
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Nuclear Envelope
- -separates the contents of the nucleus from the cytoplasm
- -two phospholipid bilayer membranes
- -underlying nuclear lamina and nuclear pore complexes
- -outer membrane continuous with the E.R.
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Nuclear Pore Complexes
- -allow selective traffic of proteins and RNAs through the nuclear envelope
- -critical role in regulating gene expression, RNA processing and ribosome assembly
- -eight fold symmetry
- -30 times the size of a ribosome, needed because ribosomes are made in the nucleus and need to be transported to the cytoplasm
- -composed of 30-50 nucleoporins
- -very high transport rate
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Structure of Nuclear Pore (pic)
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Traffic through Nuclear Pore
- -small hydrophobic molecules pass freely across pore
- -two mechanisms for polar molecule passing
- -passive-molecules less than 20-40 kDa
- -energy dependent- all larger molecules (most proteins and RNA)
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NLS
- -nuclear localization signals
- -specific AA that are recognized by transport receptors and direct the transport of proteins from cytoplasm into nucleus
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Nuclear Transport Receptors
-proteins that recognize NLS and mediate transport across nuclear envelope
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Karyopherins
- -family of nuclear transport receptors
- -importins are karyopherins that direct nuclear import
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System for Protein Import into Nucleus
- -specific importin binds to NLS (nuclear localization signal) of a protein in cytoplasm to be transported
- -importin then crosses nuclear pore while carrying cargo protein
- -importin/protein complex is acted on by active Ran complex that splits off protein and actively transports importin complex back out of nucleus (costs GTP)
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Transport of Proteins from Nucleus
- -use NES (nuclear export signals-specific AA sequences that target proteins for export from the nucleus)
- -NES interact with exportins (also members of the karyopherin family)
- -similar mechanism to importin
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