Transporters Flashcards
Rank in order of permeability:
Ions, small uncharged polar molecules, gases, non-polar molecules, large uncharged polar molecules
Highest permeability:
Gases (diffusion)
Non-polar/hydrophobic molecules (diffusion)
Small uncharged polar molecules (facilitated diffusion)
Large uncharged polar molecules (facilitated diffusion)
Ions (active transport or facilitated diffusion)
What is the difference between active transport and passive transport?
Active: requires energy, positive free energy, goes against the concentration gradient
Passive: requires no energy, negative free energy, goes with the concentration gradient
What are the various ways molecules can pass through the membrane?
Active transport: (carrier proteins)
Primary AT - uniporter, requires ATP
Secondary AT - cotransporter (supporter, antiporter), requires pre-existing electrochemical gradient
Passive transport:
Facilitated diffusion: carrier protein
Simple diffusion: channel proteins and directly through the membrane
What is the equation for net rate of diffusion?
J = P*(C2-C1)
Net rate of diffusion = Permeability * (Concentration difference)
What is the equation for free energy change?
G = RT*log(C2/C1)
Free energy change = gas constant * temperature * log(concentration outside / concentration inside)
What does Na+K+ATPase do?
Primary transporter (uses ATP) Transports 3 Na+ ions out of a cell while co-transporting 2 K+ ions into the cell (generating negative cell Potential)
What are the components of the P-type ATPase (NaK-pump)?
Alpha subunit:
Contains phosphorylated Aspartate
Binding site for Na+, K+, ATP, Oubain (Toxin that inhibits)
Beta subunit:
Contains glycoproteins that direct the pump the the cell surface membrane
What does Ca2+Mg2+ATPase do and describe its properties
Transports either Ca2+ or Mg2+ out of the cell
Primary (requires ATP)
Uniporter
High affinity, low capacity
What does the Na+Ca2+Exchanger (NCX) do and describe its properties
Transports Ca2+ out of the cell for every 3 Na+ it transports into the cell
Secondary (requires on electrochemical gradient of Na+)
Antiporter
Low affinity, high capacity
What does the Na+H+ Exchanger do?
Transports 1 H+ out of the cell for every Na+ it transports into the cell
Antiporter
What does the Na+ Glucose Co-transporter do?
Transports 1 glucose into the cell for every 2 Na+ it also transports into the cell
Symporter
What transporters are involved in cystic fibrosis?
CFTR (Cystic Fibrosis Transmembrane conductance Regulator): transports Cl- out of cells into the alveolar space
If this fails, less Cl- ions in the airway, less water, thicker mucous
What transporters are involved in diarrhoea?
CFTR (Cystic Fibrosis Transmembrane conductance Regulator): transports Cl- out of cells into the lumen of the gut
Protein kinase A causes increased Cl- efflux, more water in the lumen, watery faeces
How is Intracellular [Ca2+] controlled?
Primary active transport: PMCA and SERCA
Secondary active transport: NCX
Facilitated diffusion: Uniports into the mitochondria
How do the PMCA and SERCA work?
Both are primary transporters (requiring ATP), taking Ca2+ from the cytosol (symporting with H+)
PMCA (Plasma Membrane Ca2+ ATPase): Ca2+ —> extracellularly
SERCA (Sarco/endoplasmic Reticulum Ca2+ ATPase): Ca2+ —> S/ER
What happens when Intracellular [Ca2+] gets too high?
Uniporters transport Ca2+ into the mitochondria for storage
High [Ca2+] in the mitochondria can lead to apoptosis (initiate caspase cascade)
What does electrogenic mean?
Which transporter show electrogenicity?
Current flows in the direction of the membrane potential
NCX
How is cell pH controlled?
Acid efflux (NaH Exchanger, Na dependent HCO3 cotransporter) Alkali influx (NA dependent HCO3 cotransporter, Na+HCO3- cotransporter) Alkali efflux (AE)
How do the acid effluxers work?
Na+H+ Exchanger; As 1 Na+ moves in, 1 H+ moves out
Na+ dependent HCO3- cotransporter: As 1 HCO3- moves in, 1 Cl- moves out this is dependent on 1 Na+ moves in, as 1 H+ moves out (acid effluxer and alkali influxer)
How do the alkali influxers work?
Na+ dependent HCO3- cotransporter: As 1 HCO3- moves in, 1 Cl- moves out this is dependent on 1 Na+ moves in, as 1 H+ moves out (acid effluxer and alkali influxer)
Na+ HCO3- Exchanger: As 1 Na+ moves in so does 3 HCO3-
How does the alkali effluxer work?
AE (Anion Exchanger): As 1 Cl- moves in, 1 HCO3- moves out
Band 3 is responsible for this exchange
How is cell volume controlled?
Movement of osmotically active ions with H2O
How is HCO3- reabsorbed in the proximal tubule of the kidney?
NaHCO3 dissociates in the lumen of the kidney —> Na+, HCO3-
Na+ moves into the kidney cell via Na+H+Exchanger bringing H+ into the lumen
H+ and HCO3- form carbonic acid (H2CO3)
Carbonic anhydrase breaks down H2CO3 —> H2O +CO2 which diffuse into the kidney cell
Carbonic acid is reformed from H2O +CO2 by carbonic anhydrase
H2CO3 dissociates into H+, HCO3-
HCO3- is transported into the capillary via Band 3 (AE) with Cl- entering kidney cell
What is the Extracellular, Cytosolic, Reticulum concentration of Ca2+?
Extracellular: 10^-3
Cytosolic: 10^-7
Reticulum: 10^-5
