Membrane Transport Flashcards
What is permeable to the phospholipid bilayer?
Urea, ethanol, CO2, N2, O2, water
-low in cholesterol is more permeable to water. More cholesterol=less permeable to water
Electrochemical gradient
Combined effects of concentration and electric gradients on the direction of movement across a membrane
The 3 categories of membrane transport proteins
Channels, transporters, and ATP-powered pumps
Channels
- multiple subunits arranged around central water filled pore
- water, ions, small hydrophilic can move through
- selective and very rapid movement down conc gradient.
- most are gated
Transporters (carrier proteins)
- bind substrate with high specificity
- no direct connection between ECM and cytoskeleton
- undergo change in conformation, much slower than channels but can move larger molecules
Cotransporters
Couple transport of a substrate against its gradient with one with the gradient. Secondary active transport since against the gradient is maintained by an active transport system.
-symporter(same direction) and antiporter(opposite directions)
ATP powered pumps
- Use energy from the hydrolysis of ATP against gradients.
- have ATPase domain that catalyzes ATP hydrolysis
- primary active transport
- undergo conformational changes during process
Aquaporins
- integral membrane channel that selectively transports water.
- waters main route, also transports small solutes but impermeable to charged particles
- always open
Ion channels
-Ions flow thru ion channels passively down their electrochemical gradient
-selective
-different types.
Leak (always open)
Gated (open and close in response to stimulus)
3 properties of carrier mediated transporters
Specificity, competition, saturation
Na+/glucose cotransporter 1 (SGLT1)
- small intestines and kidney
- symporter of Na and glucose (from intestinal lumen to epithelial cells lining the small intestine)
- 1 glucose (against gradient) per 2 Na (down its gradient)
- Na provides energy for glucose to go against gradient (secondary active transport)
Chloride-bicarbonate exchanger (RBCs)
- antiporter
- function is to increases CO2 carrying capacity of blood
Na/K pump (ATPase)
Maintains concentration gradients for each.
- moves 3 Na out of cell, 2 K into cell for each ATP
- P class pump
V class pumps
Energy from ATP hydrolysis to pump H+ against gradient from cytoskeleton to intracellular organelles
F class pumps
- inner mitochondrial membrane
- protons moving down gradient in F0 domain generates formation of ATP in F1 domain
- aka ATP synthase