Membrane Transport

Question 1

What is permeable to the phospholipid bilayer?

Answer 1

Urea, ethanol, CO2, N2, O2, water

-low in cholesterol is more permeable to water. More cholesterol=less permeable to water

Question 2

Electrochemical gradient

Answer 2

Combined effects of concentration and electric gradients on the direction of movement across a membrane

Question 3

The 3 categories of membrane transport proteins

Answer 3

Channels, transporters, and ATP-powered pumps

Question 4

Channels

Answer 4

• 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

Question 5

Transporters (carrier proteins)

Answer 5

• 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

Question 6

Cotransporters

Answer 6

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)

Question 7

ATP powered pumps

Answer 7

• Use energy from the hydrolysis of ATP against gradients.
• have ATPase domain that catalyzes ATP hydrolysis
• primary active transport
• undergo conformational changes during process

Question 8

Aquaporins

Answer 8

• integral membrane channel that selectively transports water.
• waters main route, also transports small solutes but impermeable to charged particles
• always open

Question 9

Ion channels

Answer 9

-Ions flow thru ion channels passively down their electrochemical gradient
-selective
-different types.
Leak (always open)
Gated (open and close in response to stimulus)

Question 10

3 properties of carrier mediated transporters

Answer 10

Specificity, competition, saturation

Question 11

Na+/glucose cotransporter 1 (SGLT1)

Answer 11

• 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)

Question 12

Chloride-bicarbonate exchanger (RBCs)

Answer 12

• antiporter

- function is to increases CO2 carrying capacity of blood

Question 13

Na/K pump (ATPase)

Answer 13

Maintains concentration gradients for each.

• moves 3 Na out of cell, 2 K into cell for each ATP
• P class pump

Question 14

V class pumps

Answer 14

Energy from ATP hydrolysis to pump H+ against gradient from cytoskeleton to intracellular organelles

Question 15

F class pumps

Answer 15

• inner mitochondrial membrane
• protons moving down gradient in F0 domain generates formation of ATP in F1 domain
• aka ATP synthase