They can increase the rate of biochemical reactions at least a millionfold. Ferritin is a protein that combines with iron to store it in the liver. Proteins guide the flow of electrons in photosynthesis . Hormones are proteins that transmit information between specific cells and organs in complex organisms. Proteins control the passage of molecules across the membranes that surround cells and cell organelles.
Antibodies are highly specific proteins in the immune systems of complex organisms.
They recognize and combine with bacteria, viruses, and other foreign proteins to defend against intruders and protect against disease. Proteins are crucial components of muscle. Muscle contraction results from the sliding of two different protein filaments past each other. The movement of chromosomes during mitosis and the action of sperm flagella as the swim are produced by contractile structures consisting of proteins. Proteins are important in the proper and efficient functioning of sight, hearing, and other senses.