Membrane transport

Question 1

Permeability through synthetic lipid bilayers is determined by

Answer 1

1. molecular size
2. electrical charge
3. lipid solubility of molecule
4. hydrophobicity and hydrophilicity

Question 2

What are the least and most easily permeable molecules?

Answer 2

Most to Least
hydrophobic molecules (O2, CO2, N2)
Small, uncharged, polar molecules (H20, glycerol, NH3)
large, uncharged polar molecules (glucose, sucrose)
ions (Na+, K+, Cl-, etc)

Question 3

What causes ions to be so impermeable?

Answer 3

they have strong electrical charges and hydration shells that form as the charges associated with water.

Question 4

What are ion channels?

Answer 4

transmembrane proteins that conduct ions at high rates. they possess aqueous pore that is shielded from the bilayer. ion channels can have gates and be highly selective and mediate passive transport by simple diffusion

Question 5

What are transporters?

Answer 5

membrane proteins that transport solutes across bilayers. They bind more strongly than channels but weaker than pumps. Slower than channels because they toggle between two conformations in order to transport solutes. (passive transport moves along gradient)

Question 6

define passive and active transport

Answer 6

passive: solute moves along electrochemical gradient
active: solute moves against electrochemical gradient, must have energy input either directly or indirectly

Question 7

Primary active transport

Answer 7

solutes are transported against their gradient by a transporter protein (pump) that consumes energy (directly uses energy)

Question 8

secondary active transport

Answer 8

solutes are transported against their gradient using a concentration or electrochemical gradient established by a pump (indirectly uses energy)

Question 9

how does coupled (secondary active) transport work?

Answer 9

one solute moves downhill along its gradient and the energy release of this action drives transport of a second molecule uphill against its gradient. phosphorylation of a pump transporter protein using ATP drives a conformational change that transports solutes against gradient.

Question 10

types of coupled transporter proteins

Answer 10

symporter: two molecular sublates are transported in the same direction
antipoert: two molecular substrates transported in opposite directions

Question 11

P-type pumps

Answer 11

use autophosphorylation (using ATP) to power transport of ions agains gradient

Question 12

F-type pumps

Answer 12

operate in opposite direction as P-type, uses electrochemical gradient for H+ to synthesize ATP fro ADP and Pi

Question 13

ABC transporters

Answer 13

uses ATP hydrolysis to transport small molecules against gradients (doesn’t actually phosphorylate itself, just causes hydrolysis)

Question 14

What type of pump is the Na+/K+ pump? What are three important features of the pump?

Answer 14

P-type pump

1. rheogenic: generates electric current across PM
2. electrogenic: changes the voltage across the PM by -5 mV
3. ubiquitous: present in nearly every eukaryotic cell

Question 15

how much ATP consumption is due to the Na+/K+ pump?

Answer 15

about 33%

Question 16

describe the pumping cycle of the Na+/K+ pump

Answer 16

1. 3 intracellular Na+ ions bind to the pump and trigger autophosphorylation. One ATP is consumed
2. phosphorylation triggers conformational change, ejecting the 3 Na+ ions to extracellular solution
3. 2 K+ extracellular ions bind the pump, triggering dephosphorylation
4. dephosphorylation triggers release of K+ into cytosol

Question 17

what does Ouabain do?

Answer 17

Ouabain is a poisonous glycoside that at high concentrations will block the Na+/K+ APTase, but at low concentrations will stimulate it.

Question 18

what does digitoxin do?

Answer 18

(comes from foxglove plant)
digitoxin inhibits the Na+/K+ ATPase and produces a decrease in intracellular K+ and increase in intracellular Na+. This reduces efficiency of an secondary active transporter protein known as Na+/Ca2+ exchanger and increases resting intracellular Ca2+, producing an increased cardiac output

Question 19

ABC proteins are also known as

Answer 19

MDR (multiple drug resistant) proteins

Question 20

What diseases are associated with ABC proteins?

Answer 20

Cystic Fibrosis is a result of a mutated cystic fibrosis transmembrane regulator (type of ABC protein)
Cancer cells with over expressed MDR proteins (ABC transporters) can convey resistance to anti-cancer drugs and foil effective chemotherapy.