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CELL BIOLOGY: Transport through the plasma membrane
The plasma membrane is semipermeable, and its permeability depends on the size of the
molecules that want to pass trough and the lipid solubility
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In order for the cell to survive, some materials need to go in and other ones
need to go out
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Diffusion and Facilitated diffusion (passive transport): molecules go inside or outside
travelling through its concentration gradient
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2
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Hence, we need to hydrolise ATP to have energy
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Type of molecules involved in the transport:
1
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They are
usually closed but, once they are open, they allow the pass of polar residues, which are
never going to be in contact of the lipids (hydrophobic) in the membrane
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2
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They can act as passive or active
transporters
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Voltage gates channels: controlled by membrane potential
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This
process is very important in neurons
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Ligand gates channels: controlled by binding a ligand
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(passive difusion, as we are not
using energy)
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Mechanically gated channels: sound waves cause the stereocilia to tilt and this causes
the channels to open and transport signal to the brain
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Uniport: if just one molecule is transported
2
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