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Membrane transport (Ionophores (Natural ionophores (Operate by cation…
Membrane transport
Ionophores
Small molecules, cyclic or acyclic
Combine polar functional groups (ethers, esters and amides) with hydrophobic regions.
Polar groups converge to a central point to bind the cation, whilst the surface is hydrophobic and can pass through the lipid of a cell membrane.
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Anionic ionophores will neutralise cation for passive charge; netural ionophores dissipate the cation charge.
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If no potential difference exists between inner and outer surfaces, it may need to pair up with an anion such as Cl-.
PD measured by sharp steplike features in a plot of current against time, indicating ions flowing through the channels as the hydrophobic region is an electrical insulator and therefore any current must be due to the movement of ions.
Natural ionophores
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Or by forming assemblies with lipophilic exteriors and polar central pores allowing ions to pass through.
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Selectivity
Selectivity of Na over other cations (K, Ca) caused by lysine groups
Due to the fact they are rigid, and have a binding environment which can onyl accommodate low numbers.
Binding strength of side chains - if they bind too strongly the ion cannot pass, the ion must bind weakly.
The stronger the interaction between the ion and the side chain, the slower the transit through the pore
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May require water, may not...
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