Some cell types in the body are worn out quickly and need to be continuously replaced as they die. Examples include the cells that line the digestive tract and most of the blood cells. The nucleus contains the cell's DNA, which in turn is composed of thousands of genes. Genes are simply stretches of precise DNA sequences. Each gene serves as a code or blueprint that instructs the body to produce a specific protein.
Most people think of proteins as a type of food energy that helps build strong muscles.
More technically, however, protein is the term for essential molecules in the body. Some proteins, such as the collagen in our skin, are important for the structure of muscles, tissues, and organs. Other proteins, including some hormones, are involved in directing a cell to become a skin cell or a brain cell or liver cell. Still other proteins are crucial in regulating the speed at which a specific cell type can proliferate. It is these growth regulatory proteins that are vitally important in controlling cell proliferation.