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M&R > Membrane Permeability > Flashcards

Membrane Permeability Flashcards

0
Q

What closes a gap junction?

A

When cellular concentration of calcium rises above 10μm

Cell becomes acidic

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1
Q

What models are there for facilitated diffusion?

A 
Protein pores (channels)
Carrier molecules (ping pong)
Protein flip flop
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2
Q

What is the carrier model for facilitated diffusion?

A

A substrate binds which causes a conformational change

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3
Q

List the different types of gates a pore can have

A

Ligand gated
Voltage gated
Gap junction

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4
Q

Where does energy come from for active transport?

A

Hydrolysis of ATP
Electron transport
Light

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5
Q

Why does a membrane act as a permeability barrier to hydrophilic molecules/ions

A

Because movement of these things across a hydrophobic core wold require a large, free energy change.

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6
Q

What important roles do transport process have across the cell membrane?

A

Maintenance of intracellular pH
Maintenance of ionic composition
Regulation of cell volume
Concentration of metabolic fuels and building blocks
Extrusion of waste products of metabolism and toxic substances
Generation of ionic gradients needed for electrical excitability of nerve and muscle

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7
Q

What is uniport?

A

When one solute species is transported from one side of the membrane to the other

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8
Q

What is co-transport?

A

When transport of one molecule depends on the simultaneous or sequential transport of another

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9
Q

What is symport

A

Co-transport when the two molecules are going in the same direction

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10
Q

What is antiport?

A

When two molecules are being transported in opposite directions

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11
Q

What does the Na-K-ATPase (Na pump) transport?

A

3 sodium out
2 potassium in
Requires ATP

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12
Q

What secondary active transport processes does the Na pump drive?

A 
Control of pH
Regulation of calcium conc
Absorption of sodium in epithelia
Nutrient uptake such as glucose from small intestine
Regulation of cell volume
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13
Q

What does the Ca-ATPase (PMCA) pump transport? And function?

A

Calcium out of the cells.

Therefore controls calcium conc in cells

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14
Q

What is the affinity and capacity of the PMCA pump? (Calcium pump)

A

High affinity and low capacity.

Means it can transport few ions at any one time but works well when there is a low concentration of ions.

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15
Q

What does the SERCA pump do?

A

Accumulates calcium into the ER while transporting H+ out at the same time.

16
Q

Affinity and capacity of SERCA?

A

High affinity, low capacity

17
Q

What does the NCX (sodium-calcium exchanger) transport?

A

3 sodium into the cell for 1 calcium out

18
Q

When is the NCX pump reversed? What effect does this have?

A

When cells are depolarised
Contribute to calcium toxicity during ischaemia
Contributes to calcium influx during a cardiac action potential

19
Q

What does sodium-hydrogen exchange (NHE) transport?

A

1 sodium in, 1 hydrogen out - electroneutral

20
Q

What is the function of the NHE?

A

Regulate cell pH and volume

21
Q

What is the NHE activated and inhibited by?

A

Activated by growth factors

Inhibited by omiloride

22
Q

What is the function of the AE

A

An acidifier

23
Q

What does the AE (anion exchange) transport?

A

Chloride in

HCO3 out

24
Q

What is the relative concentration of potassium inside the cell compared to outside?

A

Potassium is higher inside the cell than outside

25
Q

Relative concs of sodium inside the cell compared to outside?

A

Na is higher outside the cell

26
Q

Relative conc of chloride inside compared to outside?

A

Higher outside

27
Q

Relative conc of calcium inside compared to outside?

A

Lower inside

28
Q

List the ion channels which control cell pH

A 
Na-K-ATPase
Na-H exchange
Na-H and anion exchange coupled together
Na-HCO3 co-transport
Anion exchange (band 3)
29
Q

What does the glomerulus do?

A

Filters substances out of the blood into Bowman’s capsule

30
Q

How do loop diuretics work?

A

Block the NKCC2 transporter in the loop of Henle. This blocks the re-uptake of sodium into the blood, so less water follows. Reduces BP.

31
Q

What metabolites rely on the sodium gradient for their uptake into cells against their conc gradient?

A

Glucose and sodium

32
Q

Which transporters are involved in the uptake of glucose from the gut and where?

A

Na-dependent glucose symport - glucose and Na from lumen into epithelial cell
GLUT - glucose out of cell into bloodstream
Na-K-ATPase - moves sodium into blood to maintain sodium conc gradient across the cell.

33
Q

How does insulin stimulate the rate of uptake of glucose into adipose tissue and skeletal muscle?

A

Recruits GLUT-4 transporters from internal vesicular membranes to the plasma membrane to increase the transport capacity of the membrane.

34
Q

What prevents the efflux of glucose back out of the cell when circulating glucose falls a few hours after a meal?

A

On entering the cell, glucose is converted to glucose-6P. Catalysed by hexokinase/glucokinase

M&R (10 decks)

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