Molecular Movement

Question 1

What happens in diffusion?

Answer 1

Down conc. gradient

Through lipid bilayer or protein channel / carrier

No energy required

Question 2

What happens in active transport?

Answer 2

Against conc. gradient

Protein carrier

Requires energy (ATP)

Question 3

What happens as extracellular concentration increases in passive transport?

Answer 3

Rate of influx increases in proportion

Linear relationship

Question 4

How do you calculate rate of diffusion into cell?

Answer 4

Permeability coefficient multiplied by concentration gradient across membrane

Question 5

Equation for rate of diffusion into cell:

Answer 5

Vinward = PΔS

Vinward = rate of diffusion into cell

P = permeability coefficient

ΔS = conc. gradient across membrane

Question 6

How do you work out concentration gradient across membrane?

Answer 6

Outside concentration minus inside concentration

ΔS = [S]o - [S]i

Question 7

What does rate of diffusion in passive transport depend on?

Answer 7

Thickness + viscosity of membrane

Size, shape, polarity + solubility in membrane of substrate

Concentration difference!!

Question 8

What’s a partition coefficient?

Answer 8

Gives a measure of how well a substance dissolves in lipid or aqueous phase

Question 9

How do you find partition coefficient?

Answer 9

Shake substance with oil and water mixture

Measure conc. of substance in oil and water after settling

Question 10

Equation to find partition coefficient:

Answer 10

[X]oil
K = ————
[X]water

Question 11

Why does water move more quickly than expected?

Answer 11

Intrinsic protein channels transport water (aquaporins)

Question 12

What do aquaporins form in the membrane?

Answer 12

Tetramers - each monomer acts as a water channel

Question 13

What happens in diffusion through aqueous membrane channels?

Answer 13

Substance stays in aqueous solution and passes through hydrophilic channels - allow rapid transport

Question 14

How wide are aquaporins?

Answer 14

1x water molecule wide - too narrow to permit any hydrated ions to pass through

Question 15

How many aquaporins have been found in the body?

Answer 15

13

Question 16

What are protein channels like?

Answer 16

Highly specific

Transport ions

May be opened/closed by gate

Question 17

What are the types of gated protein channels?

Answer 17

Voltage gated

Ligand gated

Question 18

What happens in a voltage gated channel?

Answer 18

Potential difference inside/outside cell causes confirmation change

Question 19

What happens in a ligand gated channel?

Answer 19

Binding of chemical ligand causes conformational change

Question 20

What type of channel is a sodium channel?

Answer 20

Voltage channel

Question 21

What do sodium channels do?

Answer 21

Lined with negatively charged amino acids

Pull sodium ion away from water shell

Allow smaller sodium ion to diffuse through

Question 22

Why can’t potassium ions diffuse through sodium channels?

Answer 22

Unhydrated potassium ions too large

Question 23

What happens in a potassium channel?

Answer 23

Carbonyl oxygens strip water molecules from potassium molecule

Question 24

What is facilitated diffusion also known as?

Answer 24

Carrier mediated transport

Question 25

What can carrier mediated transport include?

Answer 25

Active transport - against conc. gradient Facilitated diffusion - down conc. gradient

Question 26

What happens in facilitated diffusion?

Answer 26

Substance binds to specific carrier which causes conformational change -> substance transported

Question 27

What is rate of diffusion in facilitated diffusion limited by?

Answer 27

Vmax of carrier protein Carrier proteins require time to open and close

Question 28

What can active transport be inhibited by?

Answer 28

Competitive inhibitors binding to active site

Question 29

Where can active transport get their energy from?

Answer 29

Directly from energy source - primary AT Secondarily from energy stored as concentration difference resulting from secondary process - secondary AT

Question 30

Example of primary AT:

Answer 30

Sodium/potassium pump Obtains energy directly from breakdown of ATP

Question 31

What does the sodium/potassium pump do?

Answer 31

Transports Na+ out of cells and K+ into cells Establishes negative voltage inside cell

Question 32

Structure of sodium/potassium pump:

Answer 32

2 K+ binding sites on external side 3 Na+ binding sites on internal side

Question 33

Where does ATPase activity occur on sodium/potassium pump?

Answer 33

Internal side

Question 34

What is the sodium/potassium pump important for?

Answer 34

Controlling cell volume Contribution to electrical potential across membrane Used to drive secondary active transport

Question 35

What happens in secondary active transport?

Answer 35

Indirect use of energy source Movement of 2 or 3 substances is linked

Question 36

What do symporters do?

Answer 36

Transport substances in same direction as ‘driver’ ion Uses electrochemical gradient

Question 37

What do antiporters do?

Answer 37

Transport substance in opposite direction of driver ion