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Lecture _3 - Amino Acids and Proteins

Lecture _3 - Amino Acids and Proteins - The Structure and...

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The Structure and Function of Large Biological Molecules Lecture #3 – Amino Acids and Proteins Campbell – Reece, 8th Edition Campbell Reece, 8th Edition Reading Assignment: Ch t 5 Chapters 5 BIOL 203 – Spring 2010 Ralph Feuer
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Functional Groups Here “R” represents the rest of the molecule H H O H H H C C H H H OH C C C H H H H H QuickTime™ and a C C H H OH O Ethanol Acetone Acetic Acid Organic compounds can contain atoms other than C and H Form “Functional Groups” Ch i d b h f d h h b d d Characterized by the types of atoms present and the way they are bonded Giving these groups special properties Bonds between C and O or N - polar covalent bonds Can form Hydrogen Bonds.
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Linking Functional Groups To Polymers Organic molecules with certain functional groups can be joined by a covalent bond formed when a molecule of water is removed Allows the creation of new types of organic molecules An ester is formed by combining An amide is formed by combining an alcohol and a carboxylic acid. an amine and a carboxylic acid . O O R-OH + HO-P-OH O - R-O-P-OH + H 2 O O - •A phosphoester is formed from an alcohol and phosphoric acid. •More than one phosphoester bond can be formed in this way linking two molecules together
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Ester Bonds Link Fatty Acid Carboxyl f l l Groups To OH- Groups Of Glycerol Fat droplets (stained red)
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Outline α -Amino Acids: Carboxyl and amino groups bonded to α -carbon Acid/Base properties Carboxyl group is proton donor Î weak acid Polypeptides and Proteins Peptide Bond join amino group of one amino acid with carboxyl group of another by forming and amide bond Amino group is proton acceptor Î weak base At physiological pH: H 3 N+-Ca-COO- Alpha carbon is tetrahedral and bonded to 4 different groups L configuration for all natural amino acids (few exceptions) between them Î Peptide Bond C-N bond has partial double bond character Peptides and Polypeptides Peptides contain relatively few amino acids linked by peptide bonds: dipeptide, tripeptide, tetrapeptide 20 different R groups Classification based on R-group - know one example from each Aliphatic-hydrophobic Aromatic-hydrophobic tetrapeptide, …. Polypeptide contains many amino acids and if there are very many amino acids one can call it protein Proteins have molecular weights > several thousand and have 3-4 levels of structure P (1°) f Polar Uncharged-hydrophilic Acidic-hydrophilic Basic-hydrophilic Primary Structure (1°) sequence of amino acids connected by peptide bonds Secondary Structure (2°) local conformation of peptide bond backbone stabilized by H- bonds: a-helix: intrachain H-bonds & b- sheet: interchain H-bonds Tertiary Structure (3°): The complete 3- dimensional structure described by the way the polypeptide chain folds back on itself; stabilized by interactions (bonds) between the amino acid R-groups. Hydrophobic Bonds & van der Walls Interactions – most important
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