ICPP - Membrane Permeability

Question 1

What is a semi permeable membrane?

Answer 1

A layer through which only allowed substances can pass.

Question 2

Why do human eyes sometimes appear red in photos?

Answer 2

The pupil normally absorbs light, but sometimes it will reflect back red light.

Question 3

Which of these molecules can pass through the membrane easily? Hydrophobic molecules, small uncharged polar molecules, large uncharged polar molecules, ions.

Answer 3

Hydrophobic and small uncharged polar molecules.

Question 4

H2O has a very high permeability coefficient. What does this mean in regards to the amount of time it takes for a molecule of H2O to pass through the membrane?

Answer 4

It does not take long.

Question 5

Which two factors does the rate of passive transport depend on?

Answer 5

Permeability and concentration gradient.

Question 6

True or false - the rate of passive transport decreases linearly with increasing concentration gradient.

Answer 6

False - it increases.

Question 7

What are the roles of transport processes?

Answer 7

Maintenance of ionic composition, pH and volume of cell; expulsion of waste products; concentration of metabolic fuels and generation of ion gradients (for action potential).

Question 8

Why are the reciprocating and rotating models of membrane transport proteins generally regarded as wrong?

Answer 8

They require a huge amount of energy and are therefore thermodynamically unlikely.

Question 9

Which sort of ion channel is a nicotinic acetylcholine receptor?

Answer 9

Ligand-gated ion channel (ACh binds to it)

Question 10

In an ATP sensitive K+ channel, ATP binds to the channel which causes it to close. What sort of ion channel is this?

Answer 10

Ligand-gated ion channel

Question 11

Which takes longer - simple or facilitated diffusion of glucose?

Answer 11

Simple

Question 12

If delta G is positive, is the transport active or passive?

Answer 12

Active

Question 13

What two things decide whether transport is active or passive?

Answer 13

Concentration ratio and membrane potential.

Question 14

What is active transport?

Answer 14

The transport of ions or molecules against an unfavourable concentration and/or electrical gradient, which requires energy from ATP.

Question 15

Give a disadvantage of a carrier compared to a channel.

Answer 15

Carriers are slower and less efficient.

Question 16

One of these ions (Na+, K+, Cl-, Ca2+) is the odd one out and has a higher concentration inside the cell than outside. Which one?

Answer 16

K+

Question 17

What is the conc. of Na+ inside vs outside the cell?

Answer 17

Inside - 12 mM

Outside - ~145 mM

Question 18

What is the conc. of Cl- inside vs outside the cell?

Answer 18

Inside - 4.2 mM

Outside - 123 mM

Question 19

What is the conc. of Ca2+ inside vs outside the cell?

Answer 19

Inside - 10^-7 M
Outside - 1 to 1.5 mM

(Much higher outside).

Question 20

What is the conc. of K+ inside vs outside the cell?

Answer 20

Inside - 155 mM

Outside - 4mM

Question 21

What does Ca2+ ATPase (PMCA) do?

Answer 21

It transports Ca2+ ions to the outside of the membrane, which uses ATP. It is a PRIMARY ACTIVE TRANSPORTER.

Question 22

What does ATP synthase do?

Answer 22

It forms ATP from ADP as H+ ions pass through it. It is used in oxidative phosphorylation.

Question 23

What is uni-transport?

Answer 23

One molecule being transported through a membrane at a time.

Question 24

What is co-transport?

Answer 24

When more than one type of ion or molecule is transported through the membrane transporter per reaction cycle.

Question 25

What is the difference between symport and antiport?

Answer 25

They are both types of co-transport - symport is two molecules travelling in same direction together, antiport is two molecules travelling in different directions at same time.

Question 26

What does Na+K+-ATPase (sodium pump) do?

Answer 26

Pumps 3 Na+ ions out for every 2K+ ions in to cell, which is very important for action potential. Found in membrane, uses ATP (active transport), 25% of basal metabolic rate used for this pump.

Question 27

How many subunits does a sodium pump have?

Answer 27

Two - alpha contains binding sites and beta contains glycoproteins and directs pump to cell surface.

Question 28

Why are sodium pumps important in relation to action potentials?

Answer 28

They create a high intracellular K+ which maintains resting membrane potential.

Question 29

What does Ca2+Mg2+ATPase transport? What sort of transport is it?

Answer 29

It transports Ca2+ out of the cell using active transport. This is “uniport”. It has a HIGH affinity, but LOW capacity.

Question 30

What does Na+Ca2+ exchanger transport? What sort of transport is it?

Answer 30

Inward flow of 3 Na+ down conc gradient drives outward flow of one Ca2+ up gradient. This is antiport, and has LOW affinity but HIGH capacity.

Question 31

What is the function of Na+H+ exchange?

Answer 31

Inward flow of Na+ down its concentration gradient leads to cell alkalinisaion by removing H+ (antiport).

Question 32

Where does Na+glucose co-transport occur? What happens during it?

Answer 32

Small intestine and kidney, entry of 2 Na+ provides energy for entry of one glucose molecule against conc. gradient.

Question 33

Which disease occurs due to the CFTR protein not opening? Why?

Answer 33

Cystic fibrosis - Cl- ions cannot flow through so mucus is thick and sticky.

Question 34

Which diseases occurs when the CFTR protein stays open too long?

Answer 34

Cholera - flow of Cl- ions lowers water potential of lumen of intestine so diarrhoea occurs.