Membrane Permeability

Question 1

What properties/types of molecules are more permeable to pass through membranes?

Answer 1

Small, uncharged, polar. Hydrophoic

Question 2

Why can H2O pass through membranes often really easily?

Answer 2

Even though it is hydrophilic, because it is so small and polar, its small enough to pass through.

Question 3

List some molecules and why they cant pass through the membrane that easily?

Answer 3

Ions- K+, Na+, Cl-. As they have a full charge. Large polar uncharged molecules eg glucose- because theyre so big.

Question 4

What do transport processes allow to happen? What is their role?

Answer 4

Maintaining pH, ionic composition maintenance, regulate cell volume, generate ionic gradients, control conc of metabolic fuels

Question 5

Thermodynamically, what is the difference between active and passive transport?

Answer 5

Active: requires energy (+ΔG) Passive: gives off energy (-ΔG)

Question 6

List some basic ways a molecule can be transported through a membrane

Answer 6

Via a gated pore, ligand gated ion channels, voltage gated ion channels, gap junctions.

Question 7

Describe what happens with a gated pore.

Answer 7

The transporter protein undergoes a conformational change to move the substrate from one side of membrane to the other

Question 8

Describe process that happens with ligand gated ion channels

Answer 8

Ligand (eg transmitter or hormone) binds meaning the channel can then open. Eg nicotinic ACh receptor

Question 9

Describe process of how a voltage gated ion channel works

Answer 9

Membrane is usually -ve on inside and +ve on outside, if this changes causes ion channel to open

Question 10

What are gap junctions, how do they work?

Answer 10

Aggregate of intercellular channels, directly connects the cytoplasm of two cells. They allow the movement of various molecules between them

Question 11

Whether the movement across a membrane needs energy depends on….

Answer 11

• concentration ratio (if you move against, needs energy)

- membrane potential (if you move an ion to an area of the same charge, needs energy)

Question 12

List the three types of ‘porters’ and what they do

Answer 12

Uniport, symport, antiport. Uni- transports 1 thing, Sym- moves 2 at the same time from one side to the other, Anti- moves 1 from one side and 1 from another (opposites)

Question 13

When are transporters referred to as pumps?

Answer 13

When they are primary ATP transporters. (Ie ATP binds to transporter and hydrolysis occurs directly on it)

Question 14

What does active transport enable you to do?

Answer 14

Overcome unfavourable chemical or electrical gradients. They must be coupled to a thermodynamically favourable reaction.

Question 15

Which transporters are involved in the transport of calcium?

Answer 15

PMCA, SERCA, NCX, mitochondrial Ca2+ uniports

Question 16

For Na, K, Cl, Ca, state whether their conc is higher inside or outside the cell.

Answer 16

Na+ higher outside the cell. K+ higher inside the cell. Cl- higher outside. Ca2+ higher outside cell.

Question 17

What does PMCA stand for?

Answer 17

Plasma membrane Ca2+ ATPase

Question 18

What does PMCA do?

Answer 18

Pumps (1°) Ca2+ from inside cell to outside. Needs Mg2+, ATP hydrolysed directly on it. Has high affinity for Ca2+ but low capacity.

Question 19

What does SERCA stand for?

Answer 19

Sarco/endoplasmic reticulum Ca2+ ATPase

Question 20

What does SERCA do?

Answer 20

Pumps (1°) i Ca2+ into cell and H+ out. Has high affinity (stores residual Ca2+) but low capacity.

Question 21

What do mitochondrial Ca2+ uniports do?

Answer 21

Operates at high [Ca2+] to buffer Ca2+ levels. NOT ACTIVE TRANSPORT!!! Moves Ca2+ into mitochondria

Question 22

What does NCX stand for?

Answer 22

sodium (Na), Calcium eXchanger

Question 23

What does NCX do?

Answer 23

Antiporter, transports 2Ca out of the cell and transports 3Na in. Its a 2° transporter as ATP is hydrolysed elsewhere. Has low affinity, high capacity.

Question 24

When can NCX reverse? What results?

Answer 24

If the cell becomes depolarised, the 3Na+ cant be pumped to an area of +ve TF 2Ca+ are brought into the cell and 3Na+ are transported out. High levels of [Ca] are toxic to cells though

Question 25

What is passive diffusion dependant on?

Answer 25

Permeability of molecule and concentration gradient

Question 26

Describe what happens to Na+ transport during ischaemia.

Answer 26

Due to lack of perfusion, [ATP] falls, due to less ATP, Na+K+ATPase pump is inhibited. [Na+] rises in cell, cell depolarises. As a result of the depolarisation, NCX reverses (then moves Ca2+ into the cell)= toxic at high levels.

Question 27

Describe how Na+K+ATPase pump works.

Answer 27

3Na+ inside cecll bind to transporter, phosphorylated by ATP, when hydrolysed facilitates conformational change, 3Na+ released to outside cell. In new conformation, affinity for K+ is higher, 2K+ bind, gets dephosphorylated and conformation reverts, affinity lowers and 2K+ released onnside of cell.

Question 28

What is the usual amount of Na+ across a membrane?

Answer 28

145mM outside. 12mM inside.

Question 29

What is the usual amount of K+ across a membrane?

Answer 29

4mM outside. 155mM inside.

Question 30

What is the usual amount of Cl- across a membrane?

Answer 30

123mM outside. 4.2mM inside.

Question 31

What is the usual amount of Ca2+ across a membrane?

Answer 31

1.5mM outside. 10-7M inside.

Question 32

What is a common cause of drug resistance?

Answer 32

Cells extruding the drug before it can have any affect on the cell