Chapter 4: ActivitiesActivity 4.2 Facilitated Diffusion |
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Large molecules and ions cannot move
directly through cell membranes, because they cannot cross the hydrophobic portion of
the lipid bilayer. Proteins incorporated into the lipid bilayer assist these substances in
passing through the membrane by the process of facilitated diffusion. Like simple
diffusion, facilitated diffusion requires no expenditure of energy by the cell. Protein
transporters move large molecules such as glucose across the membrane. Each protein
transporter is specific for one type of molecule. Ionophores are membrane proteins that
carry ions across the membrane.
Membrane
Proteins Chapter 4, Section 4.4, Membrane Proteins |