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bioelectrochemistry - Coggle Diagram
bioelectrochemistry
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cells naturally form an electrochemical cell.
- capacitors: the lipids of the membrane are the capacitive components of the electrochemical cell
- conductors: the interaction of protein's charged groups on the surface with counter-ions in solution forms electrical double layers.
- resistance: movement of the charges inside/outside the memebrane
we can measure the difference in potential between the two different sides of the membrane and we call it the transmembrane potential or membrane potential. At the equilibrium this value is called the resting potential and it can be defined by using the Nernst equation.
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by manipulate the membrane potential with pulses of potential/current, we can allow the entrance inside the cells of different materials --> electroporation
The potential impulses that are applied with the electroporation determines the formation of pores inside the membrane. The pores easily reanneal once the potential switches off, so the cell maintains its integrity.
ACTION POTENTIAL
At rest, there are more positively charged ions outside the cell relative to the inside. Usually more than 90% of sodium and chloride ions are in the external fluids while potassium and organic ions are in the interior fluid.
We refer to this ionic imbalance as the electrochemical gradient.
When a stimulus came, it can puts the biological electrochemical cell outside the equilibrium, so outside the resting potential.
in response to the stimulus, we observe an influx of sodium through the membrane into the nerve cell and an efflux of potassium from the internal to the external fluid of the cell.
after the passage of the nerve impulse, the membrane tends to recover the initial state, This occurs through an active transport mechanism of sodium from the interior to the exterior of the cell that involves the Na,K-ATPase enzyme.
Na,K-ATPase act as channels, it open and close in response to changes in memebrane polarization. This pump is responsible for maintaining the K+ concentration gradient constant.
patch clamp
method
- A glass micropipette with a very small opening (comparable with the ion channel dimention) contains electrode + electrolyte solution. The seal between pipette and membrane is so tight that, when a single ion channel is open, all the ions flow into the pipette
- Currents fluxing through the channels, flow into the pipette and can be recorded by an electrode that is connected to a highly sensitive differential amplifier.
we can also measure the cell membrane capacitance Cm=q/Vm. So Cm defines how much charge q, is stored on 2 capacitor plates at a fixed voltage Vm.
The measurement of Cm allows also the measurement of cell area (dimension).
Cm=ε0εA/D
Thanks to this technique we are able to measure the current flow through an ion channel after activation
Normally an Ag/AgCl electrod is used. This converts ionic current in solution, into an electron current according to the following reaction:
Cl- + Ag ⇔ AgCl + e-
Due to the small currents measured (order of picoamperes), the electrode polarizations and nonlinearities are negligible.
Also the electronic ammeter must avoid appreciable noise to the currents it measures.
- charge separation
- charge transfer
