BIOL3040 Lecture Notes - Lecture 6: Nuclear Membrane, Endoplasmic Reticulum, Endomembrane System

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6 Feb 2017
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JANUARY 30 LECTURE 6
Practice Question:
What might happen to nuclear envelope breakdown during cell division if you mutated all serines, threonine,
and tyrosines of lamin proteins to alanine?
- Nuclear envelope would not break down because phosphorylation of lamins allows the nuclear
envelope to break down.
- Phosphor-null mutation: when you change an amino acid that normally gets phosphorylated to an
amino acid that cant be phosphorylated (S, T, Y gets mutated to A)
What would be the effect on the nuclear import cycle if an NLS was tethered to Ran GAP? Would the cycle
speed up, slow down, or not change?
- Because Ran GAP is high in the cytosol to convert ran GTP to Ran GDP, if Ran GAP goes in the nucleus,
it would convert GTP too early and it would not be able to continue the cycle
What if an NLS was attached to Ran GEF?
- No change because it is normally in the nucleus
What if there was constitutive ubiquitination on Ran GEF?
- Ran GEP would get broken down in the proteasome which would decrease levels of GTP in nucleus
MEMBRANE ASSEMBLY
- Membranes surround all organelles
- Endomembrane system
o Includes most of the organelles
Nuclear envelope, ER, Golgi, endosomes, lysosomes
o Interiors of the endomembrane systems are kind of like extracellular
- Endoplasmic reticulum
o Go throughout the entire cell
o Phospholipids are made on the cytosolic side of the ER
o Membrane assembly occurs in the ER
o Scramblasesin the ER that will flip phospholipids from one side to the other to equilibrate the
phospholipids
Moves it in both directions
Only in the ER
- Membrane asymmetry
o Arises in the Golgi
o Flippases and Floppases create membrane asymmetry by moving the phospholipids from one
side to another in order to separated different phospholipids
Only move in one direction
- Detergents
o Small amphipathic lipid-like molecule
o Has 1 tail instead of 2 like on the phospholipid
o Energetically more favorable to form detergent like micelles instead of a bilayer
Micelles are spheres
o When mixing detergents, it will mix and mess up cell membranes
Use for western blot
o SDS-strong ionic
Used in western blots to rip apart membranes
o Triton X-100-mild non-ionic
Poke small holes in the cellular membrane to allow antibodies to go in the cell
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