Session 3: Membrane Permiability

Question 1

What is a semi-permisible membrane?

Answer 1

A layer through which only allowed substances can pass

Question 2

What types of molecules can pass a phospholipid bilayer?

Answer 2

• hydrophobic

- small, uncharged, polar molecules

Question 3

What types of molecules cannot pass a phospholipid bilayer?

Answer 3

• large, uncharged, polar molecules

- ions

Question 4

Give an example of a molecule which can pass a phospholipid bilayer.

Answer 4

• oxygen
• carbon dioxide
• water
• urea
• glycerol
• benzene
• nitrogen

Question 5

Give an example of a molecule which cannot pass a phospholipid bilayer.

Answer 5

• glucose
• sucrose
• protons

Question 6

TRUE OR FALSE: molecules with a small permeability coefficient have a high permeability.

Answer 6

False: molecules like Na+ have a very low permeability coefficient (10^-2) and is hardly permeable

Question 7

What two factors influence passive transport?

Answer 7

1. Permeability

2. Concentration gradient

Question 8

TRUE OR FALSE: rate of passive transport doesn’t increase linearly with increasing concentration gradient

Answer 8

False

Question 9

Give 3 reasons why transport processes are so important.

Answer 9

1. Maintenance of intracellular pH
2. Regulation of cell volume
3. Maintenance if ionic composition
4. Expulsion of metabolic waste and toxic substances
5. Generation of ion gradients necessary for AP

Question 10

Why is a rotating carrier or reciprocating carrier (flip-flop) not considered the correct model for transport proteins.

Answer 10

Thermodynamically unlikely

Question 11

What does it mean if +deltaG is positive?

Answer 11

It’s active transport

Question 12

What does it mean if -deltaG is negative?

Answer 12

Passive

Question 13

Define active transport.

Answer 13

Allows the transportation of ions or molecules against an unforgivable concentration gradient. Required energy (either directly or indirectly from ATP)

Question 14

Is there more sodium ions inside or outside the cell?

Answer 14

Outside

Question 15

Is there more chloride ions inside or outside the cell?

Answer 15

Outside

Question 16

Is there more calcium ions inside or outside the cell?

Answer 16

Outside

Question 17

Is there more potassium ions inside or outside the cell?

Answer 17

Inside

Question 18

What is a primary transporter?

Answer 18

Uses ATP directly

Question 19

What is a secondary transporter?

Answer 19

Uses energy from ATP indirectly e.g. NCX

Question 20

Give an example of a primary active transporter.

Answer 20

Calcium ATPase (PMCA)

Question 21

Define unimport.

Answer 21

Movement of one molecule

Question 22

Define symport.

Answer 22

Co-transport. Movement of 2 molecules in the same direction.

Question 23

Define antiport.

Answer 23

Co-transport. Movement of 2 molecules in different directions.

Question 24

Give an example of an antiport transporter.

Answer 24

NXC

Question 25

Which ions and how many move using an NXC transporter?

Answer 25

3 sodium ions move out of the cell, 2 potassium ions move into the cell

Question 26

What transporter is important for creating a high intracellular potassium concentration?

Answer 26

• MAINLY membrane permeability for potassium ions

- secondary: sodium pump however this only generates 5-10 mV through electrogenic pump activity