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A protein molecule that consists of but a single polypeptide chain is said to be monomeric; proteins made up of more than one polypeptide chain, as many of the large ones are, are called oligomeric.
- Based upon chemical composition, proteins are divided into two major classes:
• simple proteins, which are composed of only amino acids
• conjugated proteins, which are composed of amino acids and additional organic and inorganic groupings, certain of which are called prosthetic groups.
- Conjugated proteins include glycoproteins, which contain carbohydrates.
lipoproteins, which contain lipids; and nucleoproteins, which contain nucleic acids.
- Classified by biological function:
• proteins include the enzymes, which are responsible for catalyzing the thousands of chemical reactions of the living cell.
• keratin, elastin, and collagen, which are important types of structural, or support, proteins
• hemoglobin and other gas transport proteins; ovalbumin, casein, and other nutrient molecules
• antibodies, which are molecules of the immune system (see immunity); protein hormones, which regulate metabolism and
• proteins that perform mechanical work, such as actin and myosin, the contractile muscle proteins.
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