Week 8 Pt I - Membrane Transport Part I

Question 1

What is a major property of a membrane?

Answer 1

Barrier (semi-permeable)

Question 2

What passes easily through the membrane?

Answer 2

Small non polar molecules

Question 3

What happens if molecules are charged?

Answer 3

They cannot pass through the hydrophobic part of the membrane e.g. Na+, K+ ions

Question 4

Why is a protein required?

Answer 4

Has binding side for a molecule that can change between different sides of membrane
On different sides Of membrane it must have different affinities

Question 5

On the side of membrane where the solute is a high concentration

Answer 5

Low affinity

Question 6

Who won the Nobel Prize for work on ion channels or channels that move small molecules

Answer 6

Peter Agre

Roderick MacKinnon

Question 7

What did Peter Agre’s group look at?

Answer 7

Water transport
Worked with cells with high flux of water (kidney cells and red blood cells)
Purified protein and put it in egg cells of toads
Put the cells into hypertonic and hypotonic solution
Low concentration of solute: explode
High concentration of solute: shrivel up

Question 8

Why is working with membrane proteins extremely difficult?

Answer 8

Very unstable when taken out of the membrane

Question 9

What did Roderick MacKinnon group work on?

Answer 9

Crystallised the protein KcSa1 from bacteria

It is a potassium channel

Question 10

What are two kinds of transport?

Answer 10

Down a concentration gradient - Passive Transport

Up a concentration gradient - Active transport

Question 11

What is diffusion?

Answer 11

A spontaneous movement of material from a region of high concentration to a region of low concentration

Question 12

Where does the energy come from of solute movement?

Answer 12

Entropy

Question 13

Where does the energy and change in concentration come from?

Answer 13

The change from a concentrated solution to a more dilute solution

Question 14

What does change in Gibbs Free Energy during diffusion of non electrolytes depend on?

Answer 14

Concentration gradient

Question 15

What does change in Gibbs Free Energy during diffusion of electrolytes depend on?

Answer 15

Electrochemical gradient and concentration gradient

Question 16

What is diffusion?

Answer 16

Exergonic

Question 17

What do all of our cells contain?

Answer 17

Sodium potassium pump

Question 18

What is the Faraday constant?

Answer 18

23.06kcal/v mol

Question 19

What is the electrical potential of all charged solutes?

Answer 19

Delta G = mF delta y

Question 20

What is the chemical potential of a charged solute?

Answer 20

2.3RT log10 ([Na+]i/[Na+]o)

Question 21

How does movement of ions occur?

Answer 21

Through ion channels

Question 22

What are Ion channels?

Answer 22

Selective
Bidirectional
Allowing diffusion in the direction of the electrochemical gradient

Question 23

Why does PH not change on either side of the membrane?

Answer 23

Aquaporins are present

Question 24

What is Osmosis?

Answer 24

Water moves from a region of lower solute concentration to a region of higher solute concentration

Question 25

What serves as water channels?

Answer 25

Aquaporins

Question 26

What does potassium have?

Answer 26

Solvation shelf

Question 27

What does each subunit of KcsA Contain?

Answer 27

Two transmembrane alpha helixes (M1,M2) and pore segment (P)

Question 28

What forms the selectivity filter?

Answer 28

A pentapeptide segment within P segment

Where backbone carbonyl oxygen atoms coordinate to K+ ions

Question 29

What do all ionic solutes have?

Answer 29

Hydration shell of water molecules

Question 30

What just a solute be in order to pass through the 3A pore in the ion channel?

Answer 30

Desolvated (dehydrated)

Question 31

For the smaller Na+, what does the selectivity filter provide?

Answer 31

4 coordination sites