Transport proteins may function by acting as carriers or they may provide protein-lined passages (pores) through which water-soluble materials of small molecular weight may diffuse.
Protein act as conduits to bring compounds into a cell either by passive (or facilitated) diffusion, in which no energy is needed to pass down a concentration gradient, or by active transport, for which energy is required.
The uptake of amino acids and monosaccharides occurs against a concentration gradient and requires ATP, thus, it is example of active transport.
Hemoglobin is an example of an oxygen transport protein and is part of these oxygen delivery systems.
Transport such as hemoglobin bind to specific ligands (oxygen) and transport the ligand to a site where it is needed.
Other transport proteins move about in the body fluids, carrying nutrients and other molecules from one organ to another. Those that carry lipids in the lipoproteins are examples.
Special proteins also carry fat-soluble vitamins, water-soluble vitamins, and minerals. Other example of oxygen transport protein are, myoglobin (Fe), hemerythrin (Fe), and hemocyanin (Cu).
Passive transport involved with transport of substances occurs down their concentration and electrical gradient. This does not use any energy.
A glucose transporter is an example of a passive transport protein, this protein changes shape when it binds to a molecule of glucose.
The shape change moves the solute to the opposite side of the membrane, where it detaches. Then, the transporter reverts to its original shape.
Transport Proteins in human body
