Self-Sustaining Chemical Systems:
Eucaryotic Cell Membrane
These particular antibiotics are not involved in the normal passive
transport of ions by cells, but they are believed to be models for
real carriers. Glycerol is brought into red blood cells, and galactose
into E. coli bacteria, by carriers known as permeases. These permeases
are thought to be enzymes, although little else is known about them.
All such permeases and carrier molecules are still only aids to
the movement of molecules "downhill" along a concentration gradient.
A more useful talent is the ability to carry ions or molecules from
regions where they are scarce to regions where they are already
concentrated, and to build up an excess on one side of the membrane.
ions, phosphate, sugars, and some amino acids are concentrated by
this active-transport process, which provides a way of gathering
nutrients and storing them inside the cell for later use.
Energy is required to bring things in or out against a concentration
gradient, and this energy is supplied by ATP.