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3. Proteins types are: – structural proteins (collagen in bones and keratin in hair) – contractile proteins (in muscles) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – transport proteins (hemoglobin) – immunity proteins (antibodies) – Communication (hormones) – enzymes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings a) structure a protein is a polymer constructed of amino acid monomers - a polypeptide is a chain of amino acids. Once this chain folds into a unique 3-D shape, it becomes a protein. -contain C, H, O, N Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • There are 20 types of amino acids, 9 are essential, that is animals cannot synthesize them ESSENTIAL AMINO ACIDS – these 9 are easily obtained from animal protein Methionine Valine (Histidine) – They can also be obtained from the proper combination of plant foods Threonine Phenylalanine Corn Leucine Isoleucine Tryptophan Beans and other legumes Lysine Figure 21.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings b) protein digestion Enzymes break proteins down to amino acids Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2 c) Deamination: breakdown of amino acids • occurs in the liver • deamination removes the nitrogen group from the amino acid and creates two products: – urea ---> excreted as waste (urine) – glucose ---> cellular respiration Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings d) Denaturation: polypeptide chains unravel, protein loses its specific shape and as a result, its function • caused by heat, changes in salt concentration and pH • eg: frying an egg Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings e) Diagnostic Tests for the Presence of Proteins in Food • Biuret Reagent: CuSO4 and NaOH • when proteins are present, the reagent turns from blue to purple or pink Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 3