Nearly all of the chemical reactions in our bodies, from the simple to the complex, are accelerated by the presence of biological catalysts, made from protein macromolecules, known as enzymes. Hemoglobin and Myoglobin transport oxygen first in the blood, then in the muscles. Transferrin and Ferritin carry iron in the blood and then store it in the liver. Proteins provide immune protection. The antibodies that recognize and combine with viruses, bacteria, and foreign cells are highly specific proteins.
Proteins also generate and transmit nerve impulses.
Rhodopsin, a protein photoreceptor, changes in response to the light that enters our retina. Other receptor proteins control nerve impulse transmission and the synapses or junctions between nerve cells. Proteins control growth and differentiation at many levels. At the cellular level, repressor proteins silence specific portions of DNA to help control these growth and differentiation processes. Hormones, such as insulin, human growth hormone and those that control thyroid stimulation are all proteins that control the flow of both matter and energy in our intricate bodily systems.