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Pages 42 to 46 Chemical composition Carbon Hydrogen Oxygen Nitrogen Sulfur (sometimes) Monomer/Building Block Amino Acids (20 different amino acids) Table 5-1 Fig. 5-UN1 carbon Amino group Carboxyl group Fig. 5-18 Peptide bond (a) A peptide bond is the bond joining adjacent amino acids. Side chains Peptide bond Backbone (b) Amino end (N-terminus) Carboxyl end (C-terminus) Primary - peptide bond joining adjacent amino acids Secondary - Hydrogen bonding between nonadjacent amino acids that creates an alpha helix or pleated sheets Tertiary - bond formation between R-groups; clustering of hydrophobic (nonpolar) or hydrophilic (polar) R-groups, disulfide bridges, ionic bonding, grouping based on pH, etc… that results in 3-dimensional folding Quaternary – joining of more than one polypeptide (not all proteins have this level) Fig. 5-21 Primary Structure Secondary Structure pleated sheet +H 3N Amino end Examples of amino acid subunits helix Tertiary Structure Quaternary Structure Fig. 5-21b 1 5 +H 3N Amino end 10 Amino acid subunits 15 20 25 75 80 90 85 95 105 100 110 115 120 125 Carboxyl end Fig. 5-21c Secondary Structure pleated sheet Examples of amino acid subunits helix Fig. 5-21f Hydrophobic interactions and van der Waals interactions Polypeptide backbone Hydrogen bond Disulfide bridge Ionic bond Fig. 5-21g Polypeptide chain Chains Iron Heme Chains Hemoglobin Collagen A slight change in primary structure can affect a protein’s structure and ability to function Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin Fig. 5-22 Normal hemoglobin Primary structure Primary structure Val His Leu Thr Pro Glu Glu 1 2 Secondary and tertiary structures 3 4 5 6 7 subunit Secondary and tertiary structures Sickle-cell hemoglobin Val His Leu Thr Pro Val Glu 1 2 3 Exposed hydrophobic region Quaternary structure Normal hemoglobin (top view) Quaternary structure Sickle-cell hemoglobin Function Molecules do not associate with one another; each carries oxygen. Function Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced. 10 µm Red blood cell shape Normal red blood cells are full of individual hemoglobin moledules, each carrying oxygen. 4 5 6 7 subunit 10 µm Red blood cell shape Fibers of abnormal hemoglobin deform red blood cell into sickle shape.