Molecules & Membranes

Question 1

What does amphipathic mean?

Answer 1

Containing both hydrophobic and hydrophilic parts

Question 2

What does membranes being amphipathic mean in water?

Answer 2

Membranes will spontaneously assemble mono/bilayers in water

Question 3

What do transport proteins do?

Answer 3

They provide a hydrophilic passage which allows the movement of ions and polar molecules (e.g. water) across a membrane

Question 4

What are the two main driving forces of movement across membranes?

Answer 4

• Chemical gradient (differences in concentration)
• Electrical gradient (differences in charge) - only relevant for ions

Question 5

What do the chemical and electrical gradient together make?

Answer 5

The electrochemical gradient, which is the net driving force for the movement of molecules

Question 6

What are the two transport proteins for active transport?

Answer 6

• Pumps
• Co-transport systems

Question 7

What do pumps rely on to function?

Answer 7

ATP

Question 8

Through what mechanism do pumps work?

Answer 8

Through conformational changes (changes in structure)

Question 9

How do sodium-potassium pumps create an electrical gradient?

Answer 9

• ATP hydrolyses, and the phosphate group binds to the pump protein
• This binding causes a conformational change, allowing 3 K+ ions to exit the cell
• In reverse, when the phosphate leaves and ATP is reformed, the conformational change is reversed, allowing 2 Na+ ions to enter the cell
• This creates an electrical gradient

Question 10

How do co-transporter systems work?

Answer 10

Co-transporters couple the downward movement of one ion (the driver) to the uphill movement (against the gradient) of another substance (substrate)

Question 11

What are the two different ways in which co-transporter systems work?

Answer 11

• Symport
• Antiport

Question 12

What is the general mechanism of symport co-transport systems?

Answer 12

The driver ion and substrate move in the same direction (‘piggyback’ principle)

Question 13

What is the general mechanism of antiport co-transport systems?

Answer 13

The driver ion and substrate move in opposite directions (‘revolving door’ principle)

Question 14

What are the two types of transport proteins for passive transport?

Answer 14

• Channel proteins
• Carrier proteins

Question 15

How do channel and carrier proteins work?

Answer 15

They facilitate the movement of molecules down pre-established (by active methods) electrochemical gradient

Question 16

What tends to be the difference between channel and carrier proteins?

Answer 16

• Channel proteins tend to be pores for the passage of ions
• Carrier proteins tend to undergo conformational changes that expose ion binding sites to difference sides of the membrane

Question 17

What does ‘selective’ channels mean?

Answer 17

Selectivity means that channels may have a higher permeability to certain molecules

Question 18

What does ‘gated’ channels mean?

Answer 18

Gated means that