2 ATP-dependent pumps and Ion exchangers

Question 0

Name 3 properties that means molecules cannot passively move through a membrane. Give 4 examples

Answer 0

Large, uncharged polar molecules and ions

Glucose, sucrose, H+, Cl-

Question 1

Name 3 properties of molecules that allows them to passively move through a membrane and give 4 examples

Answer 1

Hydrophobic, small, uncharged

H2O, O2, CO2, urea

Question 2

List the important functions of transport proteins (6)

Answer 2

Maintenance of ionic composition
Maintenance of intracellular pH
Regulation of cell volume
Concentration of metabolic fuels
The extrusion of waste products of metabolism
The generation of ion gradients

Question 3

Describe Ping-Pong transport

Answer 3

A membrane protein will go through a conformational change to allow a molecule through the membrane

Question 4

Explain how ‘Ligand-Gated Channels’ work

Answer 4

When a ligand such as ATP or ACh binds to the protein, the channel opens.

Question 5

Explain how ‘Voltage-Gated Channels’ open

Answer 5

The channel opens when the membrane becomes depolarised.

Question 6

Define ‘Active Transport’

Answer 6

Active transport allows the transport of molecules or ions against the concentration gradient and/or electrical gradient. It requires energy from ATP hydrolysis.

Question 7

What is the extracellular concentration of Na+?

Answer 7

145mM

Question 8

What is the extracellular concentration of Cl-?

Answer 8

123mM

Question 9

What is the extracellular concentration of Ca2+?

Answer 9

1.5mM

Question 10

What is the extracellular concentration of K+?

Answer 10

4mM

Question 11

Define Co-transport

Answer 11

More than 1 type of ion or molecule can be transported on a protein carrier per cycle.

Question 12

Describe the difference between a ‘symport’ and an ‘antiport’

Answer 12

A symport takes two molecules or ions from one side of the membrane to the other
An antiport moves one molecule or ion IN and one molecule or ion OUT of a cell.

Question 13

Describe the workings of the Na-K-ATPase pump.

Answer 13

3 Na+ ions are moved OUT of the cell. 2 K+ ions are moved IN to the cell. This movement is against the concentration gradients so ATP is required.

Question 14

What ions are moved by the PMCA protein? What is its affinity and capacity?

Answer 14

PMCA: plasma membrane calcium ATPase
Calcium is moved OUT of the cell against the concentration gradient so ATP is required. It has a high affinity for calcium but a low capacity.

Question 15

Describe and explain the actions of the Na-Ca-exchanger (NCX)

Answer 15

Exchanges 3Na+ IN for 1Ca2+ OUT in an antiport.
It works via the electrogenic current of Na+ ions. It helps to expel Ca2+ after depolarisation. The movement reverses during depolarisation.
It has a low affinity for Ca2+ but a high capacity.

Question 16

Describe the actions of the Na-H-exchanger (NHE)

Answer 16

1 Na+ is moved IN as 1H+ is moved out

Question 17

Describe the actions of the Na-glucose co-transport pump and explain how the energy is acquired.

Answer 17

1 Na+ ion and 1 glucose molecule move IN together. The movement of Na+ IN provides the energy for glucose entry against its concentration gradient.

Question 18

Explain why sufferers of CF have thick mucus

Answer 18

In CF, the CFTR gene is not present. This restricts Cl- from leaving the cell so water also remains in the cell. The mucus is therefore, very thick.

Question 19

Explain how diarrhoea occurs

Answer 19

Protein kinase A increases the expression of Cl- transport proteins. More Cl- moves OUT and so more water also moves OUT of the cell and into the gut. This results in diarrhoea.

Question 20

List 2 important functions of Na+ pumps

Answer 20

Forms Na+ and K+ gradients essential for electrical impulses

Drives secondary active transport for control of pH and regulation of cell volume.

Question 21

Describe and explain the functions of the SERCA protein

Answer 21

SERCA: Sarco/Endoplasmic Reticulum Calcium ATPase
1 Ca2+ moves IN as 1 H+ moves OUT of the SER
ATP is required as it is against the concentration gradient
It has a high affinity but a low capacity

Question 22

What is the function of mitochondrial Ca2+ uniports?

Answer 22

Act as a buffer at high concentrations of Ca2+

Question 23

Explain how ischaemia can result in toxic consequences to as cell.

Answer 23

ATP levels are depleted so the sodium pump is inhibited. Na+ accumulated in the cell and the cell depolarises. This reverses the NCX protein and Ca2+ is moved into the cell. This can be toxic to the cell.

Question 24

Name an activator and an inhibitor of the NHE pump.

Answer 24

Activator: growth factors
Inhibitor: amiloride

Question 25

Name and explain a transport protein that alkalinises a cell

Answer 25

NBC: Na+-bicarbonate-chloride co-transporter
1 Na+ ion and 1 HCO3- ion move IN
1 H+ ion and 1 Cl- ion move OUT

Question 26

Name and explain a protein transporter that acidifies a cell

Answer 26

AE: Anion Exchanger
1 HCO3- ion moves OUT
1 Cl- ion moves IN

Question 27

Explain how pH is maintained in a cell

Answer 27

pH is held at the ‘set point’. Any move away from this point is corrected by the increased activity of the NBC or AE transport proteins.

Question 28

How can a cell resist cell swelling?

Answer 28

Creating an efflux os osmotically active ions

Question 29

How can a cell resist cell shrinkage?

Answer 29

Creating an influx of osmotically active ions