STRUCTURE OF PROTEIN

PROTEIN a large polymer made up of a chain of amino acids; consists of carbon, hydrogen, oxygen, and nitrogen

AMINO ACIDS molecules of carbon, hydrogen, oxygen, and nitrogen that join together to form a protein

Like carbohydrates and fats, protein is composed of carbon, hydrogen, and oxygen. But there’s another key element that distinguishes protein from other macronutrients: nitrogen. The nitrogen is supplied by amino acids, which are the building blocks of protein.

Every amino acid consists of a central atom of carbon (C), an amino group, which contains nitrogen (written as the chemical formula NH2); an acid group (COOH), and a variable side chain. Side chains may be as simple as a single atom, or a group of as many as 19 atoms. It’s the side chains that distinguish one amino acid from another; for example, tryptophan from serine. (INFOGRAPHIC 8.2)

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INFOGRAPHIC 8.2 Amino Acids Are the Building Blocks of Protein Proteins are macronutrients made up of amino acids. They contain carbon, hydrogen, oxygen, and nitrogen.
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Question 8.2

image What is a chain of amino acids called?

A chain of amino acids is called a peptide.

PEPTIDE BOND the bond that forms between the acid group of one amino acid and the amino group of another amino acid

PEPTIDE short chain of amino acids attached together

Approximately 22,000 different proteins carry out the structural and functional roles of the body. Proteins are synthesized by linking up to 20 different amino acids by peptide bonds into chains of varying lengths. Short chains of amino acids are called peptides: a dipeptide has two amino acids, a tripeptide has three amino acids, and a polypeptide has many amino acids. All proteins are polypeptides. The sequence of the amino acids and the types of amino acids distinguish one protein from another. This can be compared with how the sequence and distribution of letters in the alphabet distinguish one word from another.

ESSENTIAL AMINO ACIDS amino acids that cannot be produced by the human body and therefore must be obtained from food

NONESSENTIAL AMINO ACIDS amino acids that the body can make and therefore need not be obtained through diet

We need all of those 20 amino acids to make the necessary proteins, but we can get them in different ways. Nine of the 20 are considered essential amino acids—we must get them from the foods we eat because they cannot be produced by the human body. The rest are nonessential amino acids—sometimes called “dispensable” amino acids—because they can be manufactured by the body.