Cell membranes, lipids.
Cell membrane is a flexible lipid bilayer. The lipid molecules (mostly phospholipids) have a polar, hydrophilic head and two hydrophobic hydrocarbon tails. Spontaneously, the lipids arrange so that the charged, acid hydrophyllic 'heads', face the (double sided) membrane exterior while the non-polar hydrophobic tails reside within the membrane's hydrophobic interior. Membranes are selectively permeable to ions and organic molecules and control the movement of substances in and out the cells.In particular, proteins on the surface are used for various functions such as cell surface receptors, enzymes, surface antigens, and transporters.
Translocation (flip-flop) and electroporation.
Cells are able to translocate lipid molecules from one layer to the other . This process is called flip-flop and it requires the polar head-group of a lipid to traverse the hydrophobic core of the membrane. The process can (i) occur through active lipid translocation driven by specific membrane proteins, flippases, (ii) occur through passive transport mechanisms, (iii) be induced by chemical means, (iv) be induced by electroporation. In electroporation, the presence of an electrostatic potential difference, and the associated electric field, in the vicinity of a membrane generates an asymmetry that profoundly affect the structure of the lipid double layer to the extent of forming pores. The pore formation minimizes the free energy of the system in the presence of the field and may be exploited to introduce substances in a cell. It may also be detrimental in practical applications, for instance when a lipid bilayer embeds a protein whose functioning changes the response of a field effect transistor.
Phys. Chem. Chem. Phys., 2011, 13, 9216–9222.
In this work, we investigate electroporation with two different electric fields, using Molecular Dynamics and discuss the time threshold of the irreversibility and the possible use of the macroscopic field to manipulate a lipid bilayer at the molecular level.
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