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ESA 2 Membranes and Receptors > Permeability Barriers (2) > Flashcards

Permeability Barriers (2) Flashcards

0
Q

What type of molecules can’t cross lipid bilayers? Give 2 examples of each.

A
  • Large uncharged polar: Glucose/Sucrose

- Ions: H+/Na+

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1
Q

What types of molecules can cross lipid bilayers. Give 2 examples of each.

A
  • Hydrophobic: O2/CO2

- Small uncharged polar: H20/urea

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2
Q

What 2 things is passive transport dependent on?

A
  • Permeability

- Concentration gradient.

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3
Q

Passive transport increases linearly with what?

A
  • Concentration gradient.
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4
Q

What are some of the roles of transport in cells?

A
  • Maintenance of ionic composition
  • Maintenance of Intracellular pH
  • Regulation of cell volume
  • Concentration of fuels and building blocks
  • Extrusion of waste products
  • Generation of ion gradients necessary for the electrical excitability of nerve and muscle.
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5
Q

What is ‘ping pong’ transport?

A
  • Substrate enters carrier protein

- Carrier protein changes shape to release substrate on other side of membrane.

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6
Q

What is facilitated diffusion?

A
  • Channel proteins are open or closed.
  • When open, allows large insoluble molecules to cross membrane.
  • Opens in response to a ligand binding.
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7
Q

Give examples of ligand gated ion channels.

A
  • Nicotinic acetylcholine receptor (Ach for Na+)

- ATP sensitive K+ channel (ATP for K+)

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8
Q

What are voltage gated ion channels?

A
  • Membrane depolarisation allows channels to open
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9
Q

What are the differences between passive and active transport?

A
  • Passive: down conc gradient, -delta G (release of energy)

- Active: against conc gradient, +delta G (requires energy)

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10
Q

What does active transport allow?

A
  • Transport of molecules against an unfavourable conc and or electrical gradient.
  • Energy is supplied directly or indirectly from ATP.
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11
Q

What are the Extracellular amounts of Na/Cl/Ca/K?

A
  • Na: 145mM
  • Cl: 123mM
  • Ca: 1.5mM
  • K: 4mM
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12
Q

What are the Intracellular values for Na/Cl/Ca/K?

A
  • Na: 12mM
  • Cl: 4.2mM
  • Ca: 1x10^-7M
  • K: 155mM
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13
Q

What does primary active transport mean?

A
  • Gets its energy from ATP directly.
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14
Q

What is 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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15
Q

What are the different types of transport through a membrane?

A
  • Uniport: Only one molecule transported in one direction
  • Symport: Two molecules transported in the same direction
  • Antiport: Two molecules transported, one in each direction.
16
Q

What is the Na/K pump?

A
  • Antiport, primary active transport.
  • Plasma membrane associated pump
  • P type ATPase: ATP phosphorylates aspartate, producing a phosphoenzyme intermediate.
17
Q
  • The Na/K pump is made up of two subunits, what are these and what are their roles?
A
  • Alpha: K/Na/ATP ouabin binding site

- Beta: Glycoprotein directs pump to surface.

18
Q

What proportion of BMR is used for the Na/K pump?

A
  • 25%
19
Q

What is the role of K being pumped through the membrane?

A
  • Responsible for membrane potential
20
Q

What are the two types of Ca transport?

A
  • Uniport: Ca-Mg ATPase.
  • High affinity, low capacity
  • Antiport: Na-Ca exchanger.
  • Low affinity, high capacity.
21
Q

What are the main two sodium transport systems?

A
  • Na-H+ exchange: inward flow of Na down conc gradient, causing cell alkalisation by removing H+ (antiport)
  • Na-glucose co-transport: entry of Na provides energy for entry of glucose against conc gradient (symport)
22
Q

What is the role of transport proteins in diarrhoea?

A
  • CFTR is overstimulated by protein kinase A

- Cl outflow increased so does H2O as it follows.

23
Q

What are the intracellular and extracellular Ca concentrations?

A
  • Intracellular: 50-100 nM

- Extracellular: 2mM

24
Q

What are the 6 different ways of controlling resting Ca?

A
  • Na/K pump using ATP
  • Ca ion channel
  • NCX (Na/Ca exchange)
  • PMCA (Ca/H exchange)
  • SERCA (Ca/H exchange in sarcoplamic reticulum)
  • Ca facilitated transport (mitochondria)
25
Q

How can NCX work in both directions?

A
  • As Na enters this causes depolarisation, membrane potential reverses mode of operation.
26
Q

How is the NCX pump affected in ischaemia?

A
  • Decrease in ATP
  • Na pump inhibited
  • Na accumulates, cell depolarises
  • NCX reverses, Na is exchanged for Ca
  • High Ca levels is toxic causing cell damage.
27
Q

What are the ways in which cell pH is controlled?

A
  • Acid extrusion: Na/H exchange -NHE
    Na dependent Cl/HCO3 exchanger -NBC
  • Base extrusion: Cl/HCO3 exchange (Cl in) -AE
28
Q

How is cell volume regulated?

A
  • Transport of osmotically active ions (Na/K/Cl/organic osmolytes)
  • Water follows
  • Cell swelling (extrude ions)
  • Cell shrinkage (influx ions)
  • Conductive and co-transport systems to maintain electroneutrality
29
Q

Outline how bicarbonate reabsorption occurs in the proximal tubule.

A
  • NaHCO3 splits into Na and HCO3-
  • Na is transported into the tubule from the lumen by NHE (Na/H)
  • Na pump, pumps Na into the capillary. (K opposite direction, but diffuses back into capillary)
  • In the proximal tubule H20 and CO2 from metabolism are combined to form H2CO3
  • This splits into HCO3- and H+
  • HCO3- is transported into the capillary by an AE pump (Cl the other way)
  • H+ is used in the NHE pump to be transported to the lumen.
  • H+ and HCO3- combine to form H2CO3
  • This can be changed into CO2 and H2O by carbonic anhydrase
  • These can be transported into the tubule.
30
Q

What are the mechanisms to resist cell swelling?

A
  • Conductive: equal ion transport (K+ and Cl- efflux)
  • Co-transport: K+ and Cl- efflux (co-transport) also amino acid and H2O out.
  • Co-transport: Cl- and HCO3- exchange and K+/H+ exchange. H+ and HCO3- combine to form H2CO3 -> H20 and CO2 which both leave the cell.
31
Q

What are the mechanisms to resist cell shrinkage?

A
  • Co-transport: Na/K and 2Cl influx. Na and organic osmolytes influx and Na/Cl influx. -> H2O influx
  • Co-transport: CO2 and H2O influx combine to form H2CO3. H2CO3 splits into H+ and HCO3-. Cl/HCO3 exchange (Cl influx, HCO3- out) H+/Na+ exchange (H+ efflux)
  • Na/Ca transported in. H2O in.

ESA 2 Membranes and Receptors (11 decks)

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