BMSC 220 Topic 8 Part 2

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BMSC 220 Topic 8 Part 2
2013-10-19 00:37:28
BMSC 220 Topic Part

BMSC 220 Topic 8 Part 2
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  1. 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.
  2. 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
  3. Structure of Nuclear Pore (pic)
  4. 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)
  5. NLS
    • -nuclear localization signals
    • -specific AA that are recognized by transport receptors and direct the transport of proteins from cytoplasm into nucleus
  6. Nuclear Transport Receptors
    -proteins that recognize NLS and mediate transport across nuclear envelope
  7. Karyopherins
    • -family of nuclear transport receptors 
    • -importins are karyopherins that direct nuclear import
  8. 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)
  9. 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