Session 2/3

Question 1

Define electrochemical gradient

Answer 1

The driving force across a plasma membrane that dictates whether an ion will move in or out of a cell, established by both the concentration difference and the electrical charge difference between the cytosilic and Extracellular surfaces of the membrane.

Question 2

What is the difference between a primary and secondary active transporter?

Answer 2

In primary active transport , the carrier protein uses energy directly from ATP hydrolysis. Whereas in secondary active transport, it uses energy stored in the concentration gradients of ions. E.G The Na+/ K+ pump creates Na+ gradient to provide energy at the expense of one ATP.

Question 3

Define
Uniport
Symport
Anti port

Answer 3

Uniport- One solute alone is transferred from one side to the other
Symport- One solute molecule relies on another molecule going in the same direction
Anti port- One solute molecule relies on another molecule travelling through the transporter in the opposite direction

Question 4

What are the functions of the Sodium-potassium pump?

Answer 4

• Forming Na+ and K+ gradients
  Driving’s many secondary active transport processes such as:
• Intracellular Ca2+ ion concentration
  -Intracellular pH
• Cell volume
  -Ion gradient underpinning the resting membrane potential
  -Nutrient uptake

Question 5

How do we control intracellular Ca2+ concentration?

Answer 5

All transporters move Ca2+ out of the cell.
Primary active transport:
1)PMCA expels Ca2+ out of cell
High affinity, low capacity.
2)SERCA accumulates Ca2+ into the SR/ER
High affinity, low capacity
Secondary Active transporters
1) Na+/ Ca2+ - Exchange (NCX)
2)Mitochondrial Ca2+ uniports

Question 6

What us Sodium- Calcium exchanger? (NCX)

Answer 6

3NA+ IN
CA2+ OUT
Net electro gradient flowing in the direction of Sodium. (Down it’s conc gradient)
When it becomes polarised

Question 7

In what ways can membrane transport processes contribute to the regulation of intracellular pH?

Answer 7

1)Movement of H+ ions and HC03- buffers pH
2)Ion transporters Na+/H+ ATPase and Cl-/HCO3- exchange to regulate pH
3)They are both secondary active transporters that regulate Ph using the Na+ gradient to provide itself with energy
4)pH is held at a set point between Na+/H+ exchange and CL-/HCO3- exchange. Any drift away is corrected by increased activity by either.
5) Acidification: activates NHE and NBC (CL-/HCO3- exchange)
Alkali is action: activates AE Anion exchange (Where HCO3- is extruded from the cell)

Question 8

Why is it clinically important to regulate intracellular pH?

Answer 8

Narrow range of Ph
Too acidic- denature get of enzymes
Too alkali- Disturbs ion movement
Denature got of enzymes too

Question 9

Why does intracellular Ca2+ need to be controlled?

Answer 9

High conc Ca2+ intracellularly is toxic to cells

Question 10

In what ways do you think cells might use membrane transport systems to maintain a constant cell volume?

Answer 10

1) Different cell types use particular combinations of transporters to achieve the regulation of transporters to achieve the regulation they need.
2) The movement of osmolytes, regulate cell volume as water follows
3) Ions: Na+, K+, Cl- ARE osmolytes
4)Cells swell: Ion extrusion
Cells shrink: Ion influx
5) Cytoskeleton- maintain appropriate cell volume

Question 11

Bicarbonate reabsorption

Answer 11

1) Almost all Na+ that appears in the glomerular filtrate is reabsorbed from kidney nephron
2) Driving force for reabsorption is low intracellular NA+ conc maintained by Na+/K+ ATPase activity in tubular cells.
3) Kidney reabsorbs all of the Bicarbonate filtered into the proximal tube.

Question 12

In an Ischemia, how does the NCX contribute to more damage?

Answer 12

1) ATP depletion causes inhibition of sodium pump
2) Accumulation Na+ in the cell, cell depolarises
3) Na+/Ca+ exchange reverses, more Ca+ into the cell
4) High Ca+, toxic, more cell death