Proteins contribute to all of the physiological functions of living organisms, notes Hyperphysics. These include transport of substances around the body and across cell membranes, catalyzing chemical reactions and providing structural integrity to organs and tissues.
Proteins are biological macromolecules that make up about 75 percent of the dry weight of the human body. The human genome codes for between 20,000 and 25,000 proteins, notes the National Institutes of Health. Some genes can code for multiple proteins, and proteins can be chemically modified,such as through phosphorylation, to alter their function according to nature, so the number of unique human protein molecules is probably much larger than this.
The functions of proteins in the human body are incredibly diverse. Hemoglobin, which resides in red blood cells, carries oxygen around the body. Potassium channels, which are present in cell membranes, allow potassium ions to pass in and out of the cell, which is vital for communication between cells in the central nervous system. Keratin is a structural protein that provides strength to hair, nails and the outer layer of skin. Myosin is a protein in muscle cells that crawls along filaments of a structural protein, actin, to cause muscle contraction. Finally hexokinase, which catalyzes the first step of glucose breakdown, is an example of an enzyme, a protein that catalyzes an energetically unfavorable chemical reaction, according to the European Bioinformatics Institute.