Membrane transport
[1] This differential expression is regulated through the differential transcription of the genes coding for these proteins and its translation, for instance, through genetic-molecular mechanisms, but also at the cell biology level: the production of these proteins can be activated by cellular signaling pathways, at the biochemical level, or even by being situated in cytoplasmic vesicles.
These transmembrane proteins possess a large number of alpha helices immersed in the lipid matrix.
[4] This structure probably involves a conduit through hydrophilic protein environments that cause a disruption in the highly hydrophobic medium formed by the lipids.
[1] These proteins can be involved in transport in a number of ways: they act as pumps driven by ATP, that is, by metabolic energy, or as channels of facilitated diffusion.
A general principle of thermodynamics that governs the transfer of substances through membranes and other surfaces is that the exchange of free energy, ΔG, for the transport of a mole of a substance of concentration C1 in a compartment to another compartment where it is present at C2 is:[5] When C2 is less than C1, ΔG is negative, and the process is thermodynamically favorable.
So, if the potential difference is maintained, the equilibrium state ΔG = 0 will not correspond to an equimolar concentration of ions on both sides of the membrane.
Where ΔGb corresponds to a favorable thermodynamic reaction, such as the hydrolysis of ATP, or the co-transport of a compound that is moved in the direction of its gradient.
As mentioned above, passive diffusion is a spontaneous phenomenon that increases the entropy of a system and decreases the free energy.
For certain solutes it was noted that the transport velocity reached a plateau at a particular concentration above which there was no significant increase in uptake rate, indicating a log curve type response.
[7] In order for an ion to pass through a pore it must dissociate itself from the water molecules that cover it in successive layers of solvation.
[7] Non-electrolytes, substances that generally are hydrophobic and lipophilic, usually pass through the membrane by dissolution in the lipid bilayer, and therefore, by passive diffusion.
There is no effective regulation mechanism that limits this transport, which indicates an intrinsic vulnerability of the cells to the penetration of these molecules.
1. phospholipid 2. cholesterol 3. glycolipid 4. sugar 5. polytopic protein (transmembrane protein) 6. monotopic protein (here, a glycoprotein) 7. monotopic protein anchored by a phospholipid 8. peripheral monotopic protein (here, a glycoprotein.)
