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Proteins AP Biology Proteins Diverse group Made of Amino Acids AP Biology 2008-2009 Proteins Most structurally & functionally diverse group Function: involved in almost everything Enzymes (pepsin, DNA polymerase) Structural Support (keratin, collagen) Transport of substances (hemoglobin, aquaporin) Hormones (insulin & other hormones) Defense (antibodies) Contraction and Movement (actin & myosin) Storage (bean seed proteins) AP Biology Proteins Structure H2O monomer = Amino Acid 20 different amino acids polymer = Chains of AA protein can be one or more polypeptide chains folded & bonded together large & complex molecules complex 3-D shape hemoglobin AP Biology Rubisco growth hormones Amino acids Structure central carbon amino group carboxyl group (acid) R group (side chain) H O H | || —C— C—OH —N— | H R variable group different for each amino acid confers unique chemical properties to each amino acid like 20 different letters of an AP Biology alphabet can make many words (proteins) Effect of different R groups: Nonpolar amino acids nonpolar & hydrophobic Why are these nonpolar & hydrophobic? AP Biology Effect of different R groups: Polar amino acids polar or charged & hydrophilic AP Biology Why are these polar & hydrophillic? Ionizing in cellular waters AP Biology H+ donors Ionizing in cellular waters AP Biology H+ acceptors Sulfur containing amino acids Form Disulfide bonds covalent cross links betweens sulfhydryls stabilizes 3-D structure H-S – S-H AP Biology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 7.12 (TEArt) ss Light chain a chain b chain s s s s s s s s ss ss Constant region Variable region S S Disulfide bond ss ss ss s s ss ss s s s s s s s s ss s s ss ss Light chain a chain Heavy chains s s s s s s b-2 microglobulin a chain b chain s s ss ss s s s s MHC-I MHC-II Plasma membrane T Receptor AP Biology B Receptor Building proteins Peptide Bond covalent bond between NH2 (amine) of one amino acid & COOH (carboxyl) of another C–N bond H2O dehydration synthesis AP Biology peptide bond Building proteins Polypeptide chains have direction N-terminus = NH2 end C-terminus = COOH end repeated sequence (N-C-C) is the polypeptide backbone can only grow in one direction AP Biology Protein structure & function Function depends on structure 3-D structure twisted, folded, coiled into unique shape pepsin hemoglobin AP Biology collagen Primary (1°) structure Chain of Amino Acids amino acid sequence determined by gene (DNA) slight change in amino acid sequence can affect protein’s structure & its 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 I’m hydrophilic! AP Biology But I’m hydrophobic! Secondary (2°) structure folding along short sections of polypeptide interactions between adjacent amino acids Hydrogen Bonds weak bonds between R groups forms sections of 3-D structure Alpha Helix B Pleated Sheet AP Biology Secondary (2°) structure AP Biology Tertiary (3°) structure interactions between distant amino acids Hydrophobic Interactions cytoplasm is water-based nonpolar amino acids cluster away from water H-Bonds Disulfide Bonds covalent bonds between sulfurs in sulfhydryls (S–H) anchors 3-D shape AP Biology Quaternary (4°) structure Consists of the interactions of two or more polypeptide chains only then does polypeptide become functional protein AP Biology = skin & tendons collagen hemoglobin Protein structure (review) R groups hydrophobic interactions disulfide bridges (H & ionic bonds) 3° multiple polypeptides hydrophobic interactions 1° amino acid sequence peptide bonds determined by DNA AP Biology 4° 2° R groups H bonds Fig. 5-21d Abdominal glands of the spider secrete silk fibers made of a structural protein containing b pleated sheets. The radiating strands, made of dry silk fibers, maintain the shape of the web. The spiral strands (capture strands) are elastic, stretching in response to wind, rain, and the touch of insects. AP Biology 2008-2009 Protein Folding in the Cell It is hard to predict a protein’s structure from its primary structure Most proteins probably go through several states on their way to a stable structure Chaperonins are protein molecules that assist the proper folding of other proteins AP Biology Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 5-24 Polypeptide Correctly folded protein Cap Hollow cylinder Chaperonin (fully assembled) AP Biology Steps of Chaperonin 2 Action: 1 An unfolded polypeptide enters the cylinder from one end. The cap attaches, causing the 3 The cap comes cylinder to change shape in off, and the properly such a way that it creates a folded protein is hydrophilic environment for released. the folding of the polypeptide. Protein denaturation Unfolding a protein alter 3-D shape some proteins can return to their functional shape after denaturation, many cannot AP Biology Let’s build some Proteins! AP Biology 2008-2009