Primary And Secondary Active Transport:

Question 1

Define primary active transport:

Answer 1

Driven directly by the energy relased by hydrolysis of ATP to ADP.

Question 2

Give some examples of primary active transporters:

Answer 2

ATPases such as:
F1F0 ATPase
Na+ -K+ ATPase

Ca2+ ATPases:
Plasma membrane Ca2+ ATPase (PMCA)
Sarco (endo)plasmic reticulum Ca2+ ATPase (SERCA)

Question 3

Define secondary active transport:

Answer 3

Driven indirectly by energy released from the hydrolysis of ATP to ADP. Energy provided by the dissipation of gradinets formed by another ion.

Question 4

Give some examples of secondary active transporters:

Answer 4

Na+ - Ca2+ exchanger (NCX)
Na+- H+ exchanger (NHE)
Na+ glucose co transport (e.g. SGTL1) (symport)

Question 5

Define co-transport:

Answer 5

More than one type of ion or molecule may be transported on a membrane transporter per reaction cycle.

Question 6

What are the two types of co transporters?

Answer 6

Symport and antiport

Question 7

Describe the Na+ K+ ATPase pump:

Answer 7

• Found on the plasma membrane.
• Primary active transporter.
• P-type ATPase
• 3Na+ out for 2K+ in

Question 8

What is the main function of the Na+ K+ ATPase pump?

Answer 8

• Generates ion gradients that are used to allow secondary active transport and action potentials.
• Only makes a small contribution to the resting membrane potential.

Question 9

Describe the chracteristics of a P-type ATPase pump:

Answer 9

• ATP phosphorylates aspartate and a phosphoenzyme intermediate is produced.
• Contains and alpha and beta subunit.

Question 10

Describe the NCX exchanger:

Answer 10

• Found on the plasma membane.
• Works via secondary active transport.
• Moves 3 Na+ into cell for 1 Ca2+ out.
• Role in expelling intracellular calcium during cell recovery.
• It has a low affinity but high capacity, therefore it is responsible for the bulk of calcium extrusion.

Question 11

How does the NCX work in ventricular myocytes?

Answer 11

• NCX activity is membrane potential dependent.
• Depolarised membrane can reverse the mode of operation of the transoprter.
• During depolarisation of cardiac action potential NCX pumps Ca2+ outwards (normal mode).
• In repolarisation of action potential NCX pumps Ca2+ inwards (reverse mode of operation).

Question 12

What role does the NCX exchanger have in cell toxicity duing ichaemia?

Answer 12

• In low oxygen states, ATP is depleted and the Na+ K+ APase pump is inhibited.
• This means that sodium accumulates and the cell depolarises.
• The NCX trnasporter reverses its mode of operation and so calcium will be pumped into the cell instead of out.
• This high intracellular calcium conc is highly toxic.

Question 13

What do acid extruders do and what is an example of one?

Answer 13

• Alkanises the cell (raises the PH).
• Secondary active transporter.
• Na+ H+ exchanger (NHE)
• Moves 1Na+ in and 1H+ out of the cell.
• Important in the kidney tubule.

Question 14

What is a base extruder and give an example of one:

Answer 14

• Acidifies the cell (decreases PH).
• Cl-/HCO3- (Anion exchanger - AE)
• Co transporter
• 1Cl- inand 1 HCO3- out.
• Found o erythrocytes and in the kidney tubule.

Question 15

What are the 3 main types of gated ion channels?

Answer 15

• Ligand gated ion channels
• Voltage gated ion channels
• Mechanically gates ion channels ( open in response to mechanical stretch of the membrane).

Question 16

Describe the two ways in which co-transport systems can be subdivided:

Answer 16

• symports - ions and molecules flow through the transporter in the same direction.
• antiports - ions and molecules flow in opposite directions across the membrane.

Question 17

Describe the anion exchanger (AE):

Answer 17

• Is an alkali extruder, therefore it acidifies the cell.
• It moves 1Cl- in and 1 HCO3- out.
• Found on erythrocytes and also kidney tubles.

Question 18

Describe the principle of cell volume regulation (how does it work)?

Answer 18

• Movement of osmotically active ions (e.g. Na+, K+, Cl-) into or out of the cell, so that water flows by osmosis.
• An influx of ions will cause the cell volume to increase whereas an efflux of ions will cause the cell volume to decrease.

Question 19

What physiological and pathological processess does calcium regulate?

Answer 19

Muscle contraction, neurotransmission, fertilisation, metabolic regulation, cell death (apoptosis/necrosis), learning and memory.

Question 20

How does the Plama membrane Ca2+ - (Mg 2+) ATPase (PMCA) pump regulate calcium levels?

Answer 20

• Found on the plasma membrane.
• Moves calcium out of the cell using ATP hydrolysis.
• Has a high affinity but low capacity, so responsible for the fine tuning of intracellular calcium levels.
• Magnesium required as a co-factor but it is not transported.

Question 21

How does the SERCA pump control calcium levels?

Answer 21

• Found on the sarcoplasmic/endoplasmic reticulum.

- Responsible for replenishing Ca2+ stores in the SR/ER.

Question 22

What are normal calcium concentrations like?

Answer 22

• Extracellular higher than intracellular.

- High intracellular calcium is toxic to cells.

Question 23

What are the 3 main types of ATPases?

Answer 23

• P-type
• F-type
• V- type

Question 24

Give an example of an F- type ATPase:

Answer 24

• F1/F0 ATPase (also known as ATP synthase).
• Function the opposite way to other ATPases.
• Allow a highly selective collapse of the H+ gradient generated by the ETC.
• They drive the synthesis of ATP.

Question 25

What are SGLT’s?

Answer 25

- Na/glucose transporters. - 5 main types. - Use either one or two Na+ ions to drive uptake of glucose against its chemical gradient.

Question 26

How many sodium molecules do SGLT1, 2 and 3 use to transport glucose?

Answer 26

- SGLT1 uses two Na+ for one glucose. | - SGLT2+3 use one Na+ for one glucose molecule.

Question 27

What are the different stages of glucose transport from the gut to the blood?

Answer 27

- SGLT1 in small intestine (gut). Co- transports glucose with Na+ so utilises secondary active transport. - Creates high conc of glucose in the intestinal epithelial cell so glucose can travel down its conc gradient into the blood by facilitated diffusion using the GLUT 2 transporter. - Blood conc of glucose low as glucose is constantly being carried away by the blood.

Question 28

What forms of transport does glucose use?

Answer 28

- Uses both secondary active transport and faciliated diffusion in the intestine and the kidneys.

Question 29

What happens to glucose in the kidneys?

Answer 29

- Glucose in blood freely passes into the glomerulus and into the tubule in the kidney. - This glucose needs to be transported back into the blood otherwise we would end up in a coma. - SGLT2 and SGLT1 transport glucose against its conc gradient into the tubule epithelia. (SGLT 1 = lower capacity higher affinity and SGLT2 = Higher capacity and lower affinity). - Glucose is then transported down its conc gradient into the blood by faciliated diffusion by GLUT2 and GLUT1.

Question 30

What GLUT transporter is found in the liver?

Answer 30

- GLUT 2 - relatively low affinity. | - Once inside the liver the glucose is converted to glucose -6 - phosphate and then into glycogen.

Question 31

What GLUT transporter is found in skeletal muscle?

Answer 31

- GLUT 4 - moderate Km. - Skeletal muscle takes up lots of glucose for utilisation or for storage as glycogen. - There is always a gradient that favours facilitated diffusion.

Question 32

Which GLUT transporter is found in adipose tissue?

Answer 32

- GLUT 4, transports glucose by faciliated diffusion.

Question 33

What GLUT transporters are used in neural tissue?

Answer 33

- GLUT 1 and GLUT 3. | - 3 carrier steps to move glucose into the neurone due to the blood brain barrier.

Question 34

Describe how GLUT4 transporters in adipose, skeletal and cardiac muscle are sensitive to insulin:

Answer 34

- When insulin is released into the blood in response to hyperglycaemia, it binds with its tyrosine kinase receptor expressed in these tissues. - This results in an intracellular signalling cascade and GLUT 4 receptors are recruited and fuse with the cell membrane. - This increases the capacity for glucose transport.

Question 35

What is the equation for wokring out PH?

Answer 35

- log [H+]

Question 36

What are PH levels above and below the normal PH range of 7.35 - 7.45 called?

Answer 36

``` Above = alkalosis Below = adidosis ```

Question 37

How would you convert a PH value to a molar (M) concentration?

Answer 37

Use calculator to do 10 to the power of -PH value.

Question 38

What is the response to cell skrinkage?

Answer 38

1) - Influx of osmotically active ions (Na+, K+ and Cl-). - The cell activates the Na+/Cl- transporter and the Na+/K+ 2Cl- co- transporter in response ot shrinkage to increase regulatory volume. 2) - The Na+/H+ exchanger can be activated to extrude H+ derived from H2CO3 dissociation in exchange for osmotically active Na+. - Extrusion of protons then results in cells alkanisation, which activates the Cl-/HCO3 anion exchanger that pulls in Cl-.

Question 39

What is the response to cell swelling?

Answer 39

- Involves the outwards transport of osmotically active ions. - K+ and Cl- activated channels allow outward movement by faciliated diffusion. - K+ /H+ transporter used - inward movement of protons will acidify the cytoplasm. - This in turn activates the cl-/HCO3- anion exchanger, which pulls in HCo3- to neutralise the H+ ion ( they combine to form H2CO3).