The human body requires three types of macronutrients – those nutrients needed in large amounts, including carbohydrates, fats and proteins. Although all macromolecules consist of oxygen, hydrogen and carbon, the amino acids that make up proteins contain between 15 and 25 percent nitrogen and some contain sulfur. Your body needs 20 different amino acids to build and repair cells and make other proteins that may function as hormones or enzymes.
Of the 20 amino acids necessary for life, your body can internally produce 11 of them. The other nine amino acids, known as the essential amino acids, come from dietary protein. When you eat foods that contain protein, like meat, dairy products, beans or legumes, your body breaks down the protein into the individual amino acids. It then uses the amino acids to build the thousands of proteins needed to support life. Some of the proteins become hormones, some become enzymes and others get incorporated into cells.
Proteins play a role in nearly every part of your body. Proteins in skin, hair, cartilage and muscle cells provide structure and protect the body. Proteins that act as enzymes, hormones and antibodies catalyze, regulate and protect the chemical reactions in the body. Proteins also play a role in the transport of oxygen and other substances in the body by making hemoglobin, the protein in red blood cells; myoglobin, the protein in muscles; and lipoproteins that transport lipids like cholesterol and triglycerides.
The human endocrine system consists of a network of organs and glands that produce the hormones. A hormone is a chemical produced in one area of the body that communicates with and controls another area of the body. Your body produces some hormones, like steroid hormones, using lipids such as cholesterol. Other types of hormones, including human growth hormone produced by the pituitary gland or insulin produced by the pancreas, are made using amino acids classifying them as protein hormones. Hormones play important roles in the body and factors that affect hormone production or function can lead to serious medical conditions like diabetes or growth disorders.
One of the main functions of proteins in the human body is to act as an enzyme – a catalyst that increases the rate of chemical reactions. Enzymes increase the rate of the thousands of reactions in the body without being consumed or altered. The orientation of the amino acids forming the protein chain determines the specific activity of the enzyme. Some enzymes consist of the protein along with other cofactors, like metal ions, or coenzymes like vitamins, needed to activate the enzyme.