Membrane Permeability

Question 1

Which 2 groups of molecules can diffuse across the phospholipid bilayer?

Answer 1

1. Hydrophobic molecules (eg. Oxygen, carbon dioxide, nitrogen)
2. Small uncharged polar molecules (eg. H20, urea, glycerol)
   (Respiratory gases and water mainly)

Question 2

Which 2 types of molecules can not diffuse across the phospholipid bilayer?

Answer 2

1. Large uncharged polar molecules (eg. Glucose and sucrose)
   ^ need some kind of aid from a protein
2. Ions

Question 3

What does the permeability coefficient show?

Answer 3

How easily a molecule passes across a bilayer

Question 4

What 2 factors effect the rate of passive transport?

Answer 4

Permeability coefficient and concentration gradient

Question 5

Does water cross a phospholipid bilayer?

Answer 5

Yes, water has a (relatively) high permeability coefficient

Question 6

What is band 3?

Answer 6

An anion exchange protein (found in bilayer and allows cl- to be transported across)

Question 7

What do transport processes in membranes do? (6)

Answer 7

1. Maintenance of ionic composition
2. Maintenance of pH
3. Regulate cell volume
4. They concentrate fuels and building blocks into the cell
5. Extrude waste/ toxic substances
6. Generate ion gradients necessary for electrical excitability

Question 8

What is the ping-pong model of membrane transport proteins?

Answer 8

The proteins are in an ‘open’ position and the substrates bind to them and cause the proteins to undergo a conformational change which allows the substrate to be released on the other side of the membrane.

Question 9

What is facilitated diffusion?

Answer 9

It occurs through ion channels that are at rest closed but when high concentrations of their ions accumulate they allow flow of ions down (can pass down a concentration or electrical gradient)

Question 10

What is a ligand?

Answer 10

A molecule which binds to a receptor and causes a conformational change

Question 11

Give an example of 2 ligand gated channels?

Answer 11

Ach binding - the acetyl choline binds to the receptor and opens it to allow sodium to pass through
ATP binding - when the amount of ATP is high inside the cell the ATP binds to the receptor and closes the gate and k+ no longer passes through

Question 12

How do voltage gated channels work?

Answer 12

There is a voltage sensor inside the gate and as the voltage inside changes it can cause repulsion to the voltage sensor. This cause the sensor to move up (and sometimes out as well) which opens the receptor gate.

Question 13

What do the facilitated transport processes do?

Answer 13

They increase the maximum velocity of diffusion

Question 14

Where does energy come from in passive transport?

Answer 14

The concentration gradient

Question 15

Will passive transport discharge or charge the membrane?

Answer 15

It will discharge as it goes in the direction of the electrical potential

Question 16

What is active transport?

Answer 16

It allows the transport of ions or molecules against the concentration or electrical gradient (either directly or indirectly energy comes from ATP)

Question 17

What percentage of ATP is used for active transport?

Answer 17

~50%

Question 18

What are the normal concentrations of Na+ inside and outside the cell?

Answer 18

Out - 145mM

In - 12mM

Question 19

What are the normal concentrations of K+ inside and outside the cell?

Answer 19

Out - 4mM

In - 155mM

Question 20

What are the normal concentrations of Ca+ inside and outside the cell?

Answer 20

Out - 1.5mM

In - 1x10-7mM

Question 21

What are the normal concentrations of Cl- inside and outside the cell?

Answer 21

Out - 123mM

In - 4.2mM

Question 22

What is a primary active trasnporter?

Answer 22

It takes ATP directly to the active site of the protein and hydrolysis it to ADP whcih causes a conformational change whcih drives Ca+ out.

Question 23

Give examples of primary active transporters?

Answer 23

Ca+ ATPase transporter
ATP synthetase (discharges protein gradient from inner membrane space of the mitochondria and drives ATP synthesis)
-the gradient is used to drive

Question 24

What is a co-transporter?

Answer 24

They transport 2 substances across the membrane either in the same direction (symport) or in opposite directions (antiport)

Question 25

How does the Na+ and K+ ATPase work?

Answer 25

It uses an antiport transporter which moves 3Na+ in to the cell and drives 2K+ out of the cell

Question 26

What type of ATPase is the Na+ and K+ ATPase?

Answer 26

P-type , the phosphate from the ATP is transferred directly onto the protein and causes a big negative charge which drives a conformational change

Question 27

What is ouabain?

Answer 27

Is a cardiac glycoside which inhibits cardiac activity (cardiac poison)

Question 28

What does electrogenic mean?

Answer 28

Causes a change on the electrical potential of a cell

Question 29

What is the Na+ - Ca+ exchanger?

Answer 29

It is a secondary active trasnporter because it uses the concentration produced by the sodium potassium ATPase and discharged the energy for the transport of calcium

Question 30

How does the Na+ -H+ exchanger work?

Answer 30

It is a secondary active transporter and it uses the concentration gradient for energy from sodium potassium pump, to alkalanise the cell by driving hydrogen ions out

Question 31

How is glucose drawn into the cell?

Answer 31

By symport active transport, the glucose is taken into the cell with a Na+ which provides the energy to go against the concentration gradient

Question 32

What happens to the transporters in patients with cystic fibrosis?

Answer 32

The transporter which transfers chloride ions across from the cell into the lumen no longer is doing this, so the mucous in the lumen doesn’t contain the chloride ions which help the control of water in tissues and creates thin, free flowing mucus.

Question 33

What happens to the cl- transporter in patients with cholera?

Answer 33

There is a build up of protein kinase A in the cell which phosphorylates the Cl- transporter protein and increases the amount of Cl- leaving the cell into the lumen which also increases the water level and in turn causes diarrhoea.