Transporter protein

A transporter protein is a protein which crosses both sides of the cell membrane and allows hydrophilic molecules to cross the membrane.

The different types of transport proteins

There are two types of transport proteins: those which facilitate the diffusion of molecules along their electrochemical gradients and those which carry the molecules actively against their electrochemical gradient.

• There are three types of the first group depending on whether or not they transport one or two molecules at the same time and on whether or not the two molecules move in the same direction. These are the uniport, symport and antiport proteins.
• The second group are called active transporters as they only function in the presence of metabolic energy (ATP). They are unable to combat the forces of the electro-chemical gradient without this energy source.