Molecules, Membrane Permeability and Structure

Organisms are not isolated system at equilibrium and need to intake nutrients and electrolytes as remove wastes. Similarly Cells within an organism must also exchange compound by passing them through membrane. The permeability of a membrane is the rate of passive diffusion of molecules through the membrane. These molecules are known as permeant molecules. Permeability depends mainly on the electric charge and polarity of the molecule and to a lesser extent the molar mass of the molecule. Compounds transported across biological membranes include: • Metabolites • Ions • Amino Adds • Nucleotide The plasma membrane is a fluid mosaic. Phospholipids form the basic structure of a cell membrane, called the lipid bilayer. Scattered in the lipid bilayer are cholesterol molecules, which help to keep the membrane fluid consistent. Membrane proteins are important for transporting substances across the cell membrane. Membrane Lipid Structure Shown is the glycerophospholipid Phosphatidylethanolamine as one possible example.

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