Topic 3B - Transport Across Membranes Flashcards
what passes via diffusion?
hydrophobic small and uncharged molecules
what do transporters and channels let through?
inorganic ions, small organic polar molecules
three types of active transport
coupled transport
ATP-driven pumps
light-driven pumps
symport vs antiport
piggyback vs go in opposite directions
what is an example of a symporter that we discussed in class?
Na+-glucose symport for maintaining low [Na+] in cell
what are the three classes of ATP-driven pumps?
P-type, V- and F-type, and ABC transporter
what kind of pumps are the Ca2+ pump and the Na-K pump examples of? And what do these pumps do?
P-type pumps: phosphorylate and transport ions. Pump Ca and Na out of cell
ABC transporters in eukaryotes vs prokaryotes?
eukaryotes = mainly export prokaryotes = important for export/ import
what type of directional transport are ABC transporters
unidirectional!
what type of things do ABC transporters transport?
ions, peptides, sugars, amino acids (small molecules)
difference between V and F type ATP-driven pumps?
V type = produce ADP from ATP
F type = produces ATP
Characteristics of Ion Channels
high selectivity/ narrow
gated
high efficiency!!!
ALWAYS PASSIVE
what are the different types of gated ion channels
voltage, extracellular ligand, intracellular ligand, mechanically (mechanosensitive)
how is the membrane potential in animal cells created?
K+ leak channel
how does K+ leak channel specificity work?
free carbonyl oxygens at selectivity filter allow dehydrated potassium to pass but sodium cannot pass because they will not be able to interact with the carbonyl oxygens as dehydrated molecules and they are too large to pass with their hydrate shells
how does the Na+ channel handle selectivity?
conducts mostly hydrated forms so Na fits and K is too big to pass
how do aquaporins work? structure and function
have hydrophilic and hydrophobic side –> hydrophilic side allows for water molecules to line up in single row and hydrophobic side makes pore too narrow for hydrated ions to enter
rapid transport of water molecules and blockage of ions (ions create osmotic gradient)
found in areas that excrete lots of water
in what type of channels is arginine important?
aquaporins (make more impermeable to hydrogen ions)
which channel has lateral ports?
voltage-gated Na+ channel
which type of channels open in an all or nothing fashion and have three distinct phases?
voltage-gated cation channels.
why is the inactive state of voltage-gated cation channels so important?
prevents signal from propagating backwards…
what did the patch clamp technique verify
that voltage-gated cation channels open in all or nothing fashion
what are transmitter-gated ion channels used for
converting extracellular chemical signals into electrical signals
what are the two types of neurotransmitters and to which ion channels are they related to?
excitatory and inhibitory neurotransmitters. related to transmitter-gated ion channels
what do excitatory neurotransmitters do?
open cation channels so the membrane depolarizes (more positive inside)
what do inhibitory neurotransmitters do?
open channels that make it more difficult for cell to depolarize (inside more negative)
what types of pumps and receptors are involved in muscular contractions
Na and Ca and acetylcholine receptors
does acetylcholine have high or low selectivity among cations?
low
how can acetylcholine receptors affect operations
block them to relax muscles
