Membrane Permeability

Question 1

What is the permeability coefficient?

Answer 1

measure of time taken to pass through the membrane, H2O = very quick, Na = very slow

dependent on permeability + concs each side

Question 2

List some of the roles of transport

Answer 2

Maintain ionic conc, intracellular pH, cell vol, conc metabolic fuels/building blocks, conc products/toxins, generate ion gradients = for electrical excitability

Question 3

What is passive transport?

Answer 3

no energy, occurs spontaneously

Question 4

What is osmotic gradient and osmosis?

Answer 4

solute gradient

passive, movement of H2O through semi-permeable membrane up solute gradient

Question 5

What is facilitated diffusion?

Answer 5

1. ion channel = movement through specific proteins
   ligand-gated ion channels
   voltage-gated ion channels
2. carrier proteins = passive movement
   large charged molecules e.g. glucose

Question 6

Describe active transport

Answer 6

energy directly/indirectly from ATP, against chem/elect gradient: Na K ATPase

Question 7

Describe secondary active transport

Answer 7

primary energy source is used indirectly

Question 8

Ca2+ ATPase what is its function?

Answer 8

primary active transporter = 1 Ca2+ out, uses ATP

Question 9

What is the Na+Ca2+ exchanger?

Answer 9

3Na+ in for 1Ca2+ out

secondary active transporter driven by Na – Antiport, co-transport

Question 10

Explain the Na+K+ATPase pump

Answer 10

moves 3 Na out, 2 K in to maintain normal conc gradient, high internal K responsible for resting membrane potential (-70mV) antiport

co-transport, active transport

P-type: phosphorylates aspartate = phosphoenzyme

Question 11

Na+ H+ exchanger what is its function?

Answer 11

1Na+ in for 1H+ out

uses Na pumped out from Na+K+ATPase, pumps back in to pump H+ out

antiport, co-transport

Question 12

How does the Na+ glucose co-transporter work?

Answer 12

entry of 2Na+ provides energy or entry of 1 glucose

symport, co-transport

Question 13

F1F0-ATPase what does this pump produce?

Answer 13

active transport in reverse mode = generates ATP by lose of H+ through ATP synthase

Question 14

Explain what a uniport is

Answer 14

one solute, one side to the other

Question 15

What is a co-transporter?

Answer 15

one solute movement dependent on another, 2 transported per reaction

Question 16

Describe co-transporters: Symport

Answer 16

2nd solute same direction

Question 17

Describe co-transporters: Antiport

Answer 17

2nd solute opposite direction

Question 18

What is an aquaporin?

Answer 18

H2O channels

Question 19

What is a gated channel?

Answer 19

Ligand gated ion channel: Ach binding, ATP-sensitive K channels (ATP binding closes channel, in DM) OR Voltage gated ion channel: membrane depolarisation, conformational change, channel opens

Question 20

Give and explain a clinical example where a pump is not functioning properly

Answer 20

Cystic fibrosis: CFTR Cl channel

Vibrio cholera infection: PKA effects CFTR = major CL lose = major water lose = diarrhoea

Question 21

Explain ball and chain inactivation.

Answer 21

Model to explain the fast inactivation mechanism of voltage gated ion channels. 3 states: OPEN: conformational change, ions flow through. CLOSED: no ion flow. INACTIVATED: blockage by ball of AA.

Question 22

How can you tell if transport is active or passive?

Answer 22

Gibbs free energy +ve = active -ve = passive

Question 23

How many folds larger is extracellular Ca than intracellular?

Answer 23

~10,000

Question 24

Why can water pass through the phospholipid bilayer easily?

Answer 24

water diffuses across as a gas

Question 25

Why does glucose pass through the phospholipid bilayer very slowly?

Answer 25

large molecule

Question 26

What is the difference between a pump and a transporter?

Answer 26

pump = found on plasma membrane

transporter = found in membranes or organelles