Living cells exhibit dramatic changes in shape that requires the fluidity of cellular membranes. The movie below uses a GFP (Green Fluorescent Protein) fusion to actin to highlight the dynamic behavior of membranes.

The amphipathic nature of lipid molecules allow them to pack tighly while also giving them a high degree of lateral mobility. Such an arrangement helps to, in part, explain the fluid nature of membranes. Maintaining fluidity is a critical part of cell homeostasis and involves remodeling of lipids in response to sudden changes in temperature. In addition, lipids are organized into microdomains (e.g., rafts) that may provide important boundaries that organize integral membrane proteins.

Membrane channels constitute the most abundant cell surface class of proteins. Generally, channels fall into two classes: those that mediate the (i) "passive" transport of solutes and those that (ii) mediate the "active" transport of solutes, usually against their concentration or electrochemical gradients through the use of an energy source (ion gradients, light, pH or ATP hydrolysis).

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