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Sem 2 - 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
Q

What happens during cholera to cause diarrhoea?

A
  • 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
Q

What are the two primary active transport process involved in Ca regulation in a cell?

A

PMCA

Serca

27
Q

When Ca is high in a cell, what else happens apart from removal out of cell and into SER?

A
  • Facilitated diffusion by uniporters into the mitochondria
  • Mitochondria act as buffers
28
Q

What happens to the NCX when the membrane is depolarised?

A
  • Product inhibition by Na+
  • Reverse mode of transport, Ca influx
29
Q

What happens to the NCX during ischaemia?

A
  • 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
Q

How does a cell sort pH out when intracellular pH is too low?

A

- NHE

- NBC

31
Q

How does a cell sort the pH out when too high?

A

- Anion exchanger (band 3)

32
Q

What does NHE regulate and what is it activated and inhibited by?

A
  • pH and cell volume
  • Activated by growth factors (found in highly metabolic tissues)
  • Inhibited by drug amiloride
33
Q

What are all of the transportes involved in cellular pH regulation?

34
Q

How is the pH of a tissue defined?

A

On the type of transporters

Transporters set the set point and regulate the pH when it moves out of the set point

35
Q

How do you regulate cell volume?

A
  • Move osmotically active ions (Na,K,Cl) or AA
  • Water will follow
  • Electcroneutral transport

Cell shrinkage: influx ions

Cell swelling: remove ions

36
Q

What are a few examples of transporter pairs involved in preventing cell swelling?

A
  • Move ions without changing electrochemical gradient
37
Q

What are a few examples of transporter pairs involved in prevent cell shrinking?

38
Q

How and why is bicarbonate reabsorbed in the proximal tubule?

A
  • Reabsorbed to retain a base in the blood that acts as a buffer to pH
39
Q

What are diuretics primarly used to treat and how do they work?

A
  • Hypertension and Oedema
  • Block transporters to prevent Na+ being reabsorbed into blood
  • More Na+ excreted, therfore more water excreted
  • Lowers blood volume
40
Q

What are some common diuretics?

A
  • Loop diuretics (thick ascending limb)
  • Thiazides (DCT)
  • Amiloride (DCT)
  • Spironolactose
41
Q

How do loop diuretics work?

A
  • Inhibit NKCC2 so Na+ cannot be moved from filtrate to cells
  • Occurs in thick ascending limb
42
Q

How do thiazides and amiloride work?

A
  • In DCT
  • Thiazides block NCCT
  • Amiloride blocks ENaC
43
Q

What aldosterone do in the kidney?

A
  • Mineralcorticoid hormone produced by adrenal cortex
  • Acts as transcription factor when binding to its receptor
  • Stimulates synthesis od ROMK, Na/K ATPase, ENaC
44
Q

What is sprironolactone?

A
  • 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
Q

What is hyperaldosteronism and how can it be treated?

A
  • Body produces too much aldosterone which causes hypertension and low blood K levels
  • Give amiloride and spironolactone which act in collecting duct
46
Q

Why does drinking alcohol cause hyperosmotic urine?

A
  • 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
Q

How do you raise intracellular Ca levels?

48
Q

How are sugars absorbed across the small intestine?

49
Q

How are amino acids absorbed in the small intestine?

Sem 2 - ICPP (12 decks)

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