membrane transport Flashcards
what do membranes do?
compartmentalize!
what are lipid bilayers permeable to?
some non-polar compounds, polar molecules require protein mediated transport
what must spontaneous passive transport be?
down a concentration gradient, active transport is up a concentration gradient which requires energy
what can transport be facilitated by?
channels!
what are the different types of facilitated channels?
non-stoichiometric
always passive
selective
gated
what are transporters?
stoichiometric
passive or active
specific
regulated
what does passive transport use?
channels (fast), transporters are slower and concentration gradients (down spont)
what does active transport use?
energy!! transporters!! using ATP coupled transport
how are ions transported?
pumps!
how is the large Na+/K+ gradient maintained?
by the Na, K-ATPase pump
even thought he cell must be a neutral charge what happens?
K+ leak channels allow some K ions to exit until the concentration gradient is balanced this creates a voltage difference across the bilayer of -70 mV (membrane potential–action potential) -ve inside relative to outside
What is the transport of ions subject to?
both concentration and voltage gradients
what are the different kinds of transport proteins?
uniport: one substance at a time
symport: two substances at a time
antiport: moves two different substances in different directions across a membrane
CONFORMATIONAL CHANGE YO
what are the topological relationships in a cell?
some things you need to a pass a membrane to get to
there is the cytosol and the extracellular space
what are protein destinations decided by?
embedded target sequences
how are proteins translocated into the ER?
signal sequence of protein binds to the translocon and the protein continues to grow into the ER the signal peptidase cuts this sequence and the tranlocon releases the protein into the ER–if opens laterally then the protein will be embedded in the membrane
how does vesicular transport work?
vesicles bud from the donor membrane and then fuse with the target membrane
where are most lipids synthesized?
in the smooth ER thus the bulk flow is directed to other membranes
what facilitates membrane fusion?
SNAREs
what does membrane diffusion depend on?
correct addressing, plus physical disruption, and reformation
what do SNARE proteins adopt?
a 4 helix bundle to drive close contact of opposing membranes and by local remodelling of the lipid composition to facilitate membrane curvature and membrane fusion
