Enzymes Substances that catalyze biological reactions classes

In Section 3.2 we introduced the basic processes of advection, diffusion, and drift, by which material is transported in biophysical systems. In this chapter we focus on a specialized class of transport transport across biological membranes. Transport of a substance across a membrane may be driven by passive permeation, as described by Equation (3.60), or it may be facilitated by a carrier protein or transporter that is embedded in the membrane. Thus transport of substances across membranes mediated by transporters is termed carrier-mediated transport. The most basic way to think about carrier proteins or transporters is as enzymes that catalyze reactions that involve transport. 

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