Lecture 18: Membrane channels and exporters

Question 1

What is passive transport?

Answer 1

Involves movement of molecules down their concentration gradient

Question 2

What is active transport?

Where does the energy come?

Answer 2

Requires an input of energy to move molecules against their concentration gradient
- Energy may come from the hydrolysis of ATP or the co-transport of another molecules down its concentration gradient

Question 3

What is co-transport?

What are the two types?

Answer 3

Is the movement of two molecules by a transporter
Symport: both molecules move in the same direction
Antiport: The two molecules move in opposite directions

Question 4

What mediated(facilitated) transport ?

Answer 4

Involves the assistance of proteins and is typical of polar molecules which are unable to move across the hydrophobic membranes

Question 5

What is non-mediated transport?

Answer 5

Does NOT require proteins and is typical of non-polar molecules

Question 6

What are membrane channels?

Answer 6

When open, a channel is open to both the intracellular and extracellular space

• Can open and close spotaneously or be ‘gated’
• Rate of transport: 10^7 - 10^8

Question 7

What are transporters?

Answer 7

Transporters are open to either the intracellular or the extracellular spaces

• binding induces a conformation change
• Rate of transport: 10^2 - 10^3 molecules per second

Question 8

What does transport of non-polar molecules depend on?

Answer 8

Transport of non-polar molecules is dependant on hydrophobicity and concentration