Membrane transport-nutrient uptake and protein excretion
Microbes import the materials needed for growth and survival from their environment and export metaborites. As describes in the previous chapter, the cytoplasm is separated from the environment by the hydrophobic cytoplasmic membrane, which is impermeable to hydrophilic solutes. Because of this permeability barrier exerted by the phospholipid component, almost all hydrophobic compounds can only pass through the membrane by means of integral membrane proteins. These are called carrier protein, transporters permeases(a website devoted entirely to transport can be found at www-biology.ucsd.edu/~msaier/transport/).
Solute transport can be classified as diffusion, active transport or group translocation according to the mechanisms involved. Diffusion does not require energy; energy is invested for active transport; and solute transported by group translocation are chemically modified during this process. Some solute are accumulated in the cell against a concentration gradient of several orders of magnitude, and energy needs to be invested for such accumulation.