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ICPP > Primary And Secondary Active Transport: > Flashcards

Primary And Secondary Active Transport: Flashcards

1
Q

Define primary active transport:

A

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

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2
Q

Give some examples of primary active transporters:

A

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

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

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3
Q

Define secondary active transport:

A

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

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4
Q

Give some examples of secondary active transporters:

A

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

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5
Q

Define co-transport:

A

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

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6
Q

What are the two types of co transporters?

A

Symport and antiport

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7
Q

Describe the Na+ K+ ATPase pump:

A
  • Found on the plasma membrane.
  • Primary active transporter.
  • P-type ATPase
  • 3Na+ out for 2K+ in
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8
Q

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

A
  • Generates ion gradients that are used to allow secondary active transport and action potentials.
  • Only makes a small contribution to the resting membrane potential.
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9
Q

Describe the chracteristics of a P-type ATPase pump:

A
  • ATP phosphorylates aspartate and a phosphoenzyme intermediate is produced.
  • Contains and alpha and beta subunit.
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10
Q

Describe the NCX exchanger:

A
  • 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.
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11
Q

How does the NCX work in ventricular myocytes?

A
  • 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).
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12
Q

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

A
  • 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.
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13
Q

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

A
  • 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.
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14
Q

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

A
  • 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.
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15
Q

What are the 3 main types of gated ion channels?

A
  • Ligand gated ion channels
  • Voltage gated ion channels
  • Mechanically gates ion channels ( open in response to mechanical stretch of the membrane).
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16
Q

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

A
  • symports - ions and molecules flow through the transporter in the same direction.
  • antiports - ions and molecules flow in opposite directions across the membrane.
17
Q

Describe the anion exchanger (AE):

A
  • Is an alkali extruder, therefore it acidifies the cell.
  • It moves 1Cl- in and 1 HCO3- out.
  • Found on erythrocytes and also kidney tubles.
18
Q

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

A
  • 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.
19
Q

What physiological and pathological processess does calcium regulate?

A

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

20
Q

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

A
  • 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.
21
Q

How does the SERCA pump control calcium levels?

A
  • Found on the sarcoplasmic/endoplasmic reticulum.

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

22
Q

What are normal calcium concentrations like?

A
  • Extracellular higher than intracellular.

- High intracellular calcium is toxic to cells.

23
Q

What are the 3 main types of ATPases?

A
  • P-type
  • F-type
  • V- type
24
Q

Give an example of an F- type ATPase:

A
  • 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.
25
Q

What are SGLT’s?

A
  • Na/glucose transporters.
  • 5 main types.
  • Use either one or two Na+ ions to drive uptake of glucose against its chemical gradient.
26
Q

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

A
  • SGLT1 uses two Na+ for one glucose.

- SGLT2+3 use one Na+ for one glucose molecule.

27
Q

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

A
  • 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.
28
Q

What forms of transport does glucose use?

A
  • Uses both secondary active transport and faciliated diffusion in the intestine and the kidneys.
29
Q

What happens to glucose in the kidneys?

A
  • 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.
30
Q

What GLUT transporter is found in the liver?

A
  • GLUT 2 - relatively low affinity.

- Once inside the liver the glucose is converted to glucose -6 - phosphate and then into glycogen.

31
Q

What GLUT transporter is found in skeletal muscle?

A
  • 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.
32
Q

Which GLUT transporter is found in adipose tissue?

A
  • GLUT 4, transports glucose by faciliated diffusion.
33
Q

What GLUT transporters are used in neural tissue?

A
  • GLUT 1 and GLUT 3.

- 3 carrier steps to move glucose into the neurone due to the blood brain barrier.

34
Q

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

A
  • 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.
35
Q

What is the equation for wokring out PH?

A
  • log [H+]
36
Q

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

A 
Above = alkalosis 
Below = adidosis
37
Q

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

A

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

38
Q

What is the response to cell skrinkage?

A

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-.

39
Q

What is the response to cell swelling?

A
  • 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).

ICPP (4 decks)

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