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Chapter 3

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CAS BI 108
Francis Monette

Savan Shah BI 108 Outline Chapter 3 Chapter 3: Proteins, Carbohydrates, and Lipids I. What Kind of Molecules Characterize Living Things -Polymers (Proteins, Carbohydrates, Lipids, and NucleicAcids) are made up of monomers • Proteins  Monomer:AminoAcids (20 possibilities) • Carbohydrates  Monomer: Monosaccharides form Polysaccharides • NucleicAcids  Monomer: Nucleotides • Lipids  Form large structures from limited set of smaller molecules • Macromolecules  Proteins, carbohydrates, lipids, and nucleic acids oFunctional groups  Certain small groups of atoms  Alcohols – OH  Aldehydes – COH  Ketones – CO  Carboxyl – COOH  Amines – NH 2  Phosphate groups – PO 4  Thiols – SH • Isomers  Molecules that have same chemical formula, but atoms are arranged differently oStructural isomers differ in how their atoms are joined together  Cis-trans isomers Atoms on same side (cis);Atoms on opposite sides (trans) oOptical isomers  Occur when carbon atom has 4 different atoms or groups of atoms attached to it (mirror image of each other) • Polymers are formed from monomers by dehydration synthesis (condensation reactions)  Formation of covalent bonds and removal of water, energy is added • When molecules break apart, the reverse happens  Hydrolysis – breakdown of polymers in their component monomers, covalent bond is broken and water molecule splits into 2 ions; release of energy II. What are the Chemical Structures and Functions of Proteins? -Amino acids are the building blocks of proteins • Only 20 amino acids • Proteins consist of 1 or more polypeptide chains  Unbranched polymers of covalently linked amino acids • Amino acids consist of: Hydrogen atom, side group, R group (variable),Amino group, Carboxyl group All connected by carbon atom oCan exist as optical isomers  D-AminoAcids (Right) and L-AminoAcids (Left) oSpecial amino acids  Cysteine, Glycine, Proline  Cysteine  Forms disulfide bridges with another cysteine side chain  Glycine  Consists of single hydrogen atom, fits in tight corners of protein molecules Savan Shah BI 108 Outline Chapter 3  Proline  Forms covalent bond with hydrocarbon side chain, resulting in ring structure oCarboxyl group of one amino acid reacts with amino group of another  Dehydration synthesis forms peptide linkage • Primary Structure  Backbone of polypeptide chain consisting of repeating –N-C-C- sequence; Sequence of amino acids in polypeptide chains determines its final shape • Secondary Structure  Consists of alpha helices and beta pleated sheets oAlpha helix  Right-handed coil that turns in same direction as a screw oBeta pleated sheet  Formed from 2 or more polypeptide chains that are almost completely extended and aligned; May form between separate polypeptide chains or between different regions of single polypeptide chain bent back on itself • Tertiary Structure  Polypeptide chain is bent at specific sites and then folded back and forth; Folds are stabilized by bonds (hydrogen bonds and disulfide bridges) • Quaternary Structure  2 or more polypeptides assemble to form larger protein molecules; Subunits bind together and interact • Environmental conditions affect protein structure oIncreases in temperature oAlterations in pH
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