Session 3: Membrane Permeability, Transporters and Ion Channels

Question 1

What is a semi-permeable membrane?

Answer 1

A layer through which only certain molecules can pass

Question 2

What types of molecules can permeate a lipid bilayer?

Answer 2

Hydrophobic molecules
Lipophilic molecules
Non-polar molecules

Question 3

What cells have a lipid bilayer?

Answer 3

ALL cells

Question 4

Passive transport of molecules through a membrane is dependent on what two things?

Answer 4

Permeability

Concentration gradient

Question 5

Give 3 examples of the important roles of transport processes in the body

Answer 5

Maintaining intracellular pH
Maintaining ionic concentrations
Regulation of cell volume
Expulsion of metabolic waste and toxic substances
Generation of ion gradients in excitable cells

Question 6

Why would reciprocating “flip-flop” and rotating carriers be very unlikely in a cell transport protein?

Answer 6

Thermodynamically not likely as it would take too much energy to achieve

Question 7

Is a gated pore that carries out “ping pong” transport an efficient method of movement molecules across a membrane?

Answer 7

No, it is very slow

Question 8

What can membrane transport proteins do instead of using inefficient “ping pong” transport?

Answer 8

Form channels which can open to allow molecules to pass in and out of the cell via facilitated diffusion

Question 9

Channels that open in response to agonist binding are known as what?
Give an example

Answer 9

Ligand-gated ion channels

Nicotinic Acetylcholine Receptor

Question 10

Channels that open in response to changes in ion current are called?
Give an example

Answer 10

Voltage-gated ion channels

Sodium (Na+) channel

Question 11

On a Michaelis- Menten curve. How would you find the Vmax and the Km

Answer 11

The Vmax is the maximum velocity or rate

The Km is the concentration at half of the Vmax

Question 12

What can we use to give a more accurate measure of Vmax and Km?

Answer 12

A double reciprocal plot

Question 13

In relation to change in Gibbs free energy, passive transport is ______ and active transport is _______.

Answer 13

• change is passive transport (-deltaG)

+ change is active transport (+deltaG)

Question 14

Whether molecules move across the membrane by active or passive transport is dependent on what two things?

Answer 14

The concentration ratio

The membrane potential

Question 15

Active transport allows the transport of _______ and molecules _________ an unfavourable concentration and or electrical gradient

Answer 15

ions

against

Question 16

True or false: Active transport can be direct or indirect

Answer 16

True

Question 17

How does direct active transport differ from indirect active transport?

Answer 17

Direct active transport involves the transporters directly binding ATP and using the energy produced. Indirect active transport uses the energy stored in the concentration gradient that has been set up by direct active transport of an ion.

Question 18

How does simple diffusion differ from facilitated diffusion?

Answer 18

Simple diffusion involves a molecule being transported across the lipid bilayer whereas facilitated diffusion involves a channel or a carrier to transport the molecule across

Question 19

What are the approximate intracellular and extracellular concentrations of Na+?

Answer 19

Intracellular: 12mM
Extracellular: 145mM

Question 20

What are the approximate intracellular and extracellular concentrations of Cl-?

Answer 20

Intracellular: 4.2mM
Extracellular: 123mM

Question 21

What are the approximate intracellular and extracellular concentrations of Ca2+?

Answer 21

Intracellular: 10^-7 M
Extracellular: 10^-3 M

Question 22

What are the approximate intracellular and extracellular concentrations of K+?

Answer 22

Intracellular: 155mM
Extracellular: 4mM

Question 23

Transport of an ion/molecule can be described as what three things depending on the number of ions and the direction of their movement?

Answer 23

Uniport
Symport
Antiport

Question 24

Symport is a type of co-transport that does what?

Answer 24

Transports different ions/molecules across the membrane at the same time, in the same direction

Question 25

Antiport is a type of co-transport that does what?

Answer 25

Transports different ions/molecules across the membrane at the same time, in different directions

Question 26

Which transporter is responsible for maintaining the concentration gradients of both K+ and Na+?

Answer 26

Na+-K+- ATPase

The sodium pump

Question 27

The Sodium Pump exchanges how many K+ for Na+ and in which direction do they both travel in relation to the cell?

Answer 27

3Na+ travel OUT of the cell

2K+ travel INTO the cell

Question 28

The setting up and maintenance of the Na+ K+ concentration gradient is essential for what?

Answer 28

Generating an action potential

Question 29

Does the Sodium-Potassium Pump use passive or active transport? Primary or secondary?

Answer 29

Active transport

Primary

Question 30

The Sodium Pump creates a _______ intracellular K+ concentration

Answer 30

High

Question 31

_____ diffusion is mainly responsible for resting membrane potential of ______ in neurones

Answer 31

K+

-70mV

Question 32

The Sodium Pump is an example of what kind of transport?

Answer 32

Antiport

Question 33

The NCX is an example of what kind of transport?

Answer 33

Antiport

Question 34

The Sodium-Hydrogen exchanger is an example of what kind of transport?

Answer 34

Antiport

Question 35

The Na+- Glucose Co transporter is an example of what kind of transport?

Answer 35

Symport

Question 36

What are the two functions of the Sodium-Potassium Pump?

Answer 36

Form Na+ and K+ gradients

Drive secondary active transport

Question 37

Pumps are only found where and use what as a primary energy source?

Answer 37

In the plasma membrane

ATP