Every type of protein is constructed of a long sequence of amino acids, which are organic compounds made up of carbon, oxygen, and hydrogen atoms. Amino acids are joined together by peptide bonds to form an amino acid chain, called a peptide. When more than 4 amino acids bond together, it is called a polypeptide. These chains can contain hundreds of amino acids. About 20 amino acids (or 22, depending on how they`re categorized) are combined to make proteins in great structural variety. Protein types number in the hundreds of thousands, each with a sequence that is unique in the number, type, order, and shape of amino acids in its chain.
This interactive shows a single amino acid which is joined by peptide bonds to three other amino acids to form a peptide. The peptide then folds and joins with other polypeptide chains to form a protein. Carbon atoms are dark gray, hydrogen atoms are white, nitrogen atoms are blue, radicals are purple, peptide bonds are green, and oxygen atoms are red.
Protein is in every living cell in the body. Our bodies need protein from the foods we eat to build and maintain bones, muscles and skin. We get proteins in our diet from meat, dairy products, nuts and certain grains and beans. Proteins from meat and other animal products are complete proteins. This means they supply all of the amino acids the body can't make on its own. Plant proteins are incomplete. You must combine different types of plant proteins to get all of the amino acids your body needs.
It is important to get enough dietary protein. You need to eat protein every day, because your body doesn't store it the way it stores fats or carbohydrates. The average person needs 50 to 65 grams of protein each day. This is the amount in four ounces of meat plus a cup of cottage cheese.
Linear POLYPEPTIDES that are synthesized on RIBOSOMES and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of AMINO ACIDS determines the shape the polypeptide will take, during PROTEIN FOLDING, and the function of the protein.
National Center for Biotechnology Information, U.S. National Library of Medicine
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