Membrane Transport

Question 1

What is membrane transport?

Answer 1

The transport of molecules across biological membranes.

Question 2

Membranes are rigid - true or false?

Answer 2

False, membranes are very wobbly

Question 3

Why is membrane transport important?

Answer 3

It protects metabolic reactions within the cell from the environment.
Communication and exchange of material between the cell and the environment.

Question 4

Membranes are walls with gates. What are these gates and what do they do?

Answer 4

Gates are transport proteins.
Transport proteins allow and control passage in and out of the cell.
They allow for controlled interaction between the cell and the environment.

Question 5

Membranes are very hydrophobic and only allow for the passage of other hydrophobic molecules. So why does water get through?

Answer 5

Water molecules are so small that some inevitably get through.

Question 6

What do transport proteins do to allow larger molecules to pass?

Answer 6

Create a hydrophilic passage
Create a filter
Provide possibility for energy coupling
Provide possibility for regulation
Facilitate diffusion by generating a hydrophilic pore

Question 7

What is facilitated diffusion?

Answer 7

Transport proteins create a hydrophilic pore that hydrophilic molecules can diffuse through.

Question 8

What are the two types of force that drive the movement of molecules across membranes.

Answer 8

Chemical gradient (concentration gradient)
Electrical gradient (charge gradient)

Question 9

What is the electrochemical gradient?

Answer 9

The net driving force for the movement of a molecule resulting from the combination of the chemical and electrical gradient.

Question 10

What does active transport do?

Answer 10

Moves substances against the electrochemical gradient and requires the input of energy.

Question 11

What does passive transport do?

Answer 11

Moves substances down the electrochemical gradient and does not require an input of energy.

Question 12

What are the transport proteins for active transport?

Answer 12

Pumps

Co-transport systems

Question 13

What are the transport proteins for passive transport?

Answer 13

Channels

Carriers

Question 14

What do pumps do?

Answer 14

Establish an electrochemical gradient which can be used to drive active transport of other molecules

Question 15

What is energy coupling?

Answer 15

ATPases: transport is coupled to the hydrolysis of ATP

Question 16

What is conformational change?

Answer 16

Same amino acid, different shape.

Energetically most favourable change

Question 17

What do co-transport systems do?

Answer 17

Couple the downward movement of one ion (driver) with the uphill movement of another solute (substrate).

Question 18

What is symport?

Answer 18

Driver ion and substrate move in same direction (piggyback principle)

Question 19

What is antiport?

Answer 19

Driver ion and substrate move in opposite direction (revolving door principle)
Protein pushes “door” allowing sugar through in the opposite direction.

Question 20

What does a channel do?

Answer 20

A channel provides an aqueous pore for passage of ions

Question 21

What does a carrier do?

Answer 21

A carrier undergoes a conformational change that exposes ion binding sites to different sides of the membrane.

Question 22

What is a selective ion channel?

Answer 22

Select which ions pass through
E.g
Some ion channels have a 100 fold higher permeability for K+ than for Na+

Question 23

What is a gated ion channel?

Answer 23

A gated ion channel can open and close upon specific stimulus