Chapter 11 Protein Proteins are mainly composed of

Chapter 11 Protein • Proteins are mainly composed of the elements carbon, hydrogen, oxygen, and nitrogen • Proteins are made up of subunits called organic acids which contain carboxyl groups (-COOH) • Organic acids in proteins are called amino acids

Amino Acids • Amino acids have three parts to their structure; a side chain of carbon and hydrogen atoms, a carboxyl group, and an amine group. • An amine group contains one nitrogen and two hydrogen atoms, (-NH 2) • When two amino acids join together the bond is called a peptide bond

Amino Acids • There are 20 amino acids that are necessary for the body to remain healthy, grow, and maintain body functions • Eight of these amino acids cannot be produced in the body and are classified as essential amino acids • Essential amino acids- amino acids that must be supplied by foods in the diet

Complete vs. Incomplete Proteins • Complete proteins- foods that contain all 8 essential amino acids • Most come from animal sources and are high quality proteins, ex. eggs, milk, fish, poultry, meats • Incomplete proteins- foods that are short of one or more of the 8 essential amino acids needed for human growth • Most come from grains, nuts, vegetables, and legumes

Protein Structures • There are infinite numbers of protein structures but they can be classified in three ways. • 1. Primary structure • 2. Secondary structure • 3. Tertiary structure

Primary Structure • Primary structure of a protein molecule is the order the amino acids occur in the chain • A result of the chain of peptide bonds formed in making the protein molecule

Secondary Structure • Secondary structure of a protein molecule refers to the shape of sections of the amino acid chain • The three patterns of secondary structures are the helix, random coil, and the pleated sheet

Tertiary Structure • Tertiary structure of a protein molecule refers to the three-dimensional structure of an entire amino acid chain • The two main tertiary structures are globular (balled up) and fibrous (strands) • Globular proteins- hemoglobin, lipoprotein, casein, and albumin • Fibrous proteins- helix shaped strands, ex. collagen, elastin, keratin, myosin are all found in muscle fibers, ligaments, tendons, hair and fingernails

Hydrophobic Interactions • A common interaction between protein molecules is a hydrophobic, or water repelling, interaction that occurs between nonpolar side chains with carbon rings • Casein, found in milk, is an example of a hydrophobic protein and is vital to the formation of curds in cheese making

Oxidation and Reduction • The reversible process of adding and removing oxygen to a compound is called oxidation and reduction • Oxidation adds oxygen to a compound • Reduction removes oxygen from a compound

Denaturation of Proteins • Denaturation- Any change of the shape of a protein molecule without breaking peptide bonds and usually results in a loosening or unfolding of the protein molecule • Denaturation is occasionally reversible but it is not when disulfide cross-links are broken

Causes of Denaturation • • Hot and cold temperatures Mechanical actions Sound waves Pressure Irradiation p. H changes Mineral salts

Heat and Denaturation • The rate of increase for protein denaturation is 600 times for every 10ºC increase in temperature

Coagulation • Coagulation- a type of permanent denaturation when a liquid or semiliquid protein forms solid or semisoft clots. • Example- milk curdling to form cheese