Membrane Trafficking Flashcards
What are liposomes?
Synthetic membrane vesicles (with a defined composition)
What property of liposomes makes them useful for the medical world?
What are they used for in the medical world?
Can surround hydrophilic/lipophilic drugs
Used as a drug delivery system
What’s the importance of proteins in membranes? (What are they used for/control?)
Signal transmittance (signal receptors) Channels for ions/solutes Control shape and long-range organisation - regulate membrane curvature - diffusion barrier
What is the key difference between membrane “trafficking” and membrane “transport”?
transport occurs across membranes
e.g. outside to inside a cell
traffic is the movement of macromolecules between membrane organelles
i.e. within a cell
What is the key advantage for eukaryotes having membrane bound organelles?
Membrane act as a barrier and can therefore provide multiple chemical environments within the same cell (this can be used to enable different functions)
How do vesicles form on membrane surfaces?
Self-assemble via large cytoplasmic protein complexes that form vesicle coats
What does “COP” stand for and what are the names of the 3 key COPs?
Coat Proteins
COPI
COPII
Clathrin adaptors
What are the two key functions of COPs?
Promote vesicle formation via membrane curvature
Trap transport membrane cargo proteins via specific signals (acting locally)
What evidence is there of coat proteins being conserved (common ‘ancestor’)?
There are 2 ancient families of coat proteins and the complexes have conserved domains
What components make up the subunit for Clathrin?
Alpha-solenoid domain
Beta-propeller domain
What is the clathrin subunit called?
beta/alpha coatomer
What are the names of the two domains that make up coat proteins called that are not involved in the clathrin subunit?
RING
Longin
How do coat proteins achieve specificity?
Different coat proteins recognise different amino acid sorting signals in the cytoplasmic domain of the cargo receptor
What part do clathrin adaptors play in trafficking?
Endocytosis and secretion
Where does COPI function?
Golgi to ER (retrieval)
What is the role of COPII?
ER to Golgi
WHat are the two Clathrin AP1/AP2 sorting signals and single letter codes?
Tyrosine YXX0
Di-Leucine [DE}XXXL[L]
What is the COP1 sorting signal and single letter code?
Di-Lysine KKXX or KXKXX (at C-terminal)
What is the COPII sorting signal and single letter code?
Di-Acidic DxE
What process triggers/promotes vesicle coat recruitment?
GTPases acting as a molecular switch (GTP binding promotes coat recruitment)
Name the 2 key proteins that specify the target membrane and the coat that they act on
ARF1 GTPase - COPI and Clathrin AP1
SAR1 GTPases - COPII
Describe the general process of GTPases acting as a molecular switch (diagram)
GTP to GDP via GEF usually turns on
Reverse via GAP using H2O to form Pi
What is the problem with spontaneous membrane fusion?
It is a very slow process and not very speific because the phospholipid bilayer leads to a negatively charged surface causing electrostatic repulsion when vesicles/membranes approach causing unfavourable fusion
What is the name of the protein used to overcome the problem of spontaneous membrane fusion?
SNARE proteins drive membrane fusion
