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Proteins AP Biology Proteins Multipurpose molecules AP Biology 2006-2007 Proteins Most structurally & functionally diverse group of biomolecules Function: involved in almost everything AP Biology enzymes (pepsin, polymerase, etc.) structure (keratin, collagen) carriers & transport (membrane channels) receptors & binding (defense: antibodies) contraction (actin & myosin) signaling (hormones: insulin) storage (bean seed proteins) Proteins Structure: monomer = amino acids 20 different amino acids polymer = polypeptide protein can be one or more polypeptide chains folded & bonded together large & complex molecules complex 3-D shape hemoglobin AP Biology growth hormones Amino acids Structure: central carbon amino group carboxyl group (acid) R group (side chain) variable group confers unique chemical properties of the amino acid AP Biology H O H | || —C— C—OH —N— | H R Nonpolar amino acids nonpolar & hydrophobic AP Biology Polar amino acids polar or charged & hydrophilic AP Biology Sulfur containing amino acids Form disulfide bridges cross links betweens sulfurs in amino acids H-S – S-H You wondered why perms smelled like rotten eggs? AP Biology Building proteins Peptide bonds linking NH2 of one amino acid to COOH of another C–N bond dehydration synthesis AP Biology peptide bond Protein structure & function Function depends on structure 3-D structure twisted, folded, coiled into unique shape pepsin hemoglobin AP Biology collagen Primary (1°) structure Order of amino acids in chain amino acid sequence determined by gene (DNA) slight change in amino acid sequence can affect protein’s structure & it’s function even just one amino acid change can make all the difference! AP Biology lysozyme: enzyme in tears & mucus that kills bacteria Sickle cell anemia AP Biology Secondary (2°) structure “Local folding” folding along short sections of polypeptide interaction between adjacent amino acids H bonds between R groups -helix -pleated sheet AP Biology Tertiary (3°) structure “Whole molecule folding” determined by interactions between R groups hydrophobic interactions effect of water in cell anchored by disulfide bridges (H & ionic bonds) AP Biology Quaternary (4°) structure More than one polypeptide chain joined together only then is it a functional protein hydrophobic interactions collagen = skin & tendons AP Biology hemoglobin Protein structure (review) R groups hydrophobic interactions, disulfide bridges 3° 1 ° multiple polypeptides hydrophobic interactions aa sequence peptide bonds determined by DNA AP Biology 2° R groups H bonds 4° Let’s build some Proteins! AP Biology 2006-2007 Protein models Protein structure visualized by X-ray crystallography extrapolating from amino acid sequence computer modelling lysozyme AP Biology Any Questions?? AP Biology 2006-2007