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09 - ICPP > 5 - Membrane Transporters 2 > Flashcards

5 - Membrane Transporters 2 Flashcards

1
Q

What is the role of the Na+/K+ ATPase transporter (antiporter)?

A
  • Forms Na+ and K+ gradients to drive secondary active transport
  • Contribute to -5mv of resting membrane potential
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2
Q

What are some of the roles of secondary active transport?

A
  • Regulate pH
  • Absorption of nutrients like glucose
  • Absorption of Na+ in the epithelia
  • Regulation of cell volume and calcium conc
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3
Q

Why are high levels of calcium toxic to a cell?

A

Calcium would react with phopshate in the cytosol and form calcium phosphate which would calcify the cell

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4
Q

Why does calcium concentration in a cell have to be controlled?

A
  • High levels toxic to cell
  • Allows cell signalling if small changes in Ca conc
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5
Q

What is a semi-permeable membrane?

A
  • A membrane that only allows select materials to diffuse through
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6
Q

What molecules can diffuse through a semi-permeable membrane directly?

A
  • Small uncharged molecule
  • Small hydrophobic molecules

H2O, O2, N2, CO2, Urea, Benzene, Glycerol

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7
Q

What does the rate of passive transport depend on?

A
  • Permeability coefficient (varies with each membrane, high number means more permeable)
  • Concentration gradient
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8
Q

Why does the model of rotating transport carriers not work in reality?

A

Proteins cannot flip-flop!!

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9
Q

What are some models of facilitated diffusion via proteins?

A

- Ping-pong (conformational change when molecules binds)

- LGIC (gated pores)

- VGIC

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10
Q

What are two examples of LGIC?

A

- Nicotinic acetylcholine

- ATP-sensitive K+ channel (normally open but when ATP is high it binds to channel and causes gate to close)

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11
Q

What is an example of a VIGC and how does it work?

A
  • Na+ channel
  • Sensitive to membrane potential
  • When membrane potential changes the gate opens as voltage sensors in the channel move up away from positive charge
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12
Q

What is the difference between active and passive transport?

A

Active has positive free energy change and passive has negative free energy change

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13
Q

What two gradients affect passive transport?

A
  • Electrochemical
  • Concentration

Linear relationship with rate of transport

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14
Q

What is the general principles of active transport?

A
  • Movement of ions or molecules against their concentration or electrochemical gradient
  • Requires energy from ATP hydrolysis
  • Cells use about 30-50% of their ATP for this
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15
Q

What sort of membrane protein do each type of molecule travel down?

A
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16
Q

What are the concentrations of the four main ions intra and extracellularly?

A
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17
Q

Is ATP synthase (F1F0) active or passive transport?

A

Active transport in reverse

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18
Q

What are the two types of co-transport?

A
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19
Q

Why does the Na+K+ ATPase require energy?

A
  • It is swapping charges but swapping three for two positive charges so needs energy to overcome this difference
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20
Q

What is the structure of the Na/K ATPase?

A
  • P-type ATPase as phosphorylated on aspartate
  • A-subunit (ATP, K, Na binding sites)
  • B-subunit ( glycoprotein directs pump to surface)
21
Q

How is calcium moved out of the cell on the plasma membrane?

A
  • PMCA (high affinity, low capacity)
  • NCX (low affinity, high capacity, 2nd active transport)

NCX when calcium high, then PMCA

22
Q

How does the Na+/H+ transporter work?

A
  • Na pump sets up Na gradient
  • Antiport
  • Secondary active transport
  • Entry of Na down it’s concentration gradient leads to cell alkalinisation by removing H+
23
Q

How does the Na/Glucose transporter work?

A
  • Secondary active transport
  • Symport
24
Q

How do chloride ions normally get from the interstitium to the lumen, and what happens during cystic fibrosis?

A
  • Transported in via Na+/2Cl-/K+ symporter down Na gradient
  • CFTR passively transfers Cl- from in cell to lumen
  • In CF, patient cant put as many CFTR proteins on membrane so less Cl- transported out of cell, less water leaves cell so sticky mucus
25
What happens during cholera to cause diarrhoea?
- Toxin activates adenylate cyclase and therefore PKA - PKA increases transport of Cl- by CFTR into the lumen - More Cl- in lumen means more water so diarrhoea
26
What are the two primary active transport process involved in Ca regulation in a cell?
PMCA Serca
27
When Ca is high in a cell, what else happens apart from removal out of cell and into SER?
- Facilitated diffusion by uniporters into the mitochondria - Mitochondria act as buffers
28
What happens to the NCX when the membrane is depolarised?
- Product inhibition by Na+ - Reverse mode of transport, Ca influx
29
What happens to the NCX during ischaemia?
- Low O2 so ATP depleted - Na pump inhibited - Accumulation of Na in cell - NCX reverse to remove Na - Ca influx uncontrolled so cell dies due to toxicity
30
How does a cell sort pH out when intracellular pH is too low?
**- NHE** **- NBC**
31
How does a cell sort the pH out when too high?
**- Anion exchanger (band 3)**
32
What does NHE regulate and what is it activated and inhibited by?
- pH and cell volume - Activated by growth factors (found in highly metabolic tissues) - Inhibited by drug amiloride
33
What are all of the transportes involved in cellular pH regulation?
34
How is the pH of a tissue defined?
On the type of transporters Transporters set the set point and regulate the pH when it moves out of the set point
35
How do you regulate cell volume?
- Move osmotically active ions (Na,K,Cl) or AA - Water will follow - Electcroneutral transport Cell shrinkage: influx ions Cell swelling: remove ions
36
What are a few examples of transporter pairs involved in preventing cell swelling?
- Move ions without changing electrochemical gradient
37
What are a few examples of transporter pairs involved in prevent cell shrinking?
38
How and why is bicarbonate reabsorbed in the proximal tubule?
- Reabsorbed to retain a base in the blood that acts as a buffer to pH
39
What are diuretics primarly used to treat and how do they work?
- Hypertension and Oedema - Block transporters to prevent Na+ being reabsorbed into blood - More Na+ excreted, therfore more water excreted - Lowers blood volume
40
What are some common diuretics?
- Loop diuretics (thick ascending limb) - Thiazides (DCT) - Amiloride (DCT) - Spironolactose
41
How do loop diuretics work?
- Inhibit NKCC2 so Na+ cannot be moved from filtrate to cells - Occurs in thick ascending limb
42
How do thiazides and amiloride work?
- In DCT - Thiazides block NCCT - Amiloride blocks ENaC
43
What aldosterone do in the kidney?
- Mineralcorticoid hormone produced by adrenal cortex - Acts as transcription factor when binding to its receptor - Stimulates synthesis od ROMK, Na/K ATPase, ENaC
44
What is sprironolactone?
- Antagonist of mineralcorticoid receptor - Therefore prevents production of ENaC, Na/K ATPase and ROMK - Na cannot be reabsorbed so retained in collecting duct and so is water
45
What is hyperaldosteronism and how can it be treated?
- Body produces too much aldosterone which causes hypertension and low blood K levels - Give amiloride and spironolactone which act in collecting duct
46
Why does drinking alcohol cause hyperosmotic urine?
- Alcohol suppresses pituitary from secreting ADH - ADH normally acts on aquaporins so body can reabsorb water quickly - No ADH, less aquaporins so not as much water reabsorbed
47
How do you raise intracellular Ca levels?
48
How are sugars absorbed across the small intestine?
49
How are amino acids absorbed in the small intestine?

09 - ICPP (12 decks)

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