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Amino Acids Proteins, and Enzymes Types of Proteins Amino Acids The Peptide Bond 1 Types of Proteins • • • • • • • Type Structural Contractile Transport Storage Hormonal Enzyme Protection Examples tendons, cartilage, hair, nails muscles hemoglobin milk insulin, growth hormone catalyzes reactions in cells immune response 2 Amino Acids • • • • Building blocks of proteins Carboxylic acid group Amino group Side group R gives unique characteristics R side chain I H2N—C —COOH I H 3 Examples of Amino Acids H I H2N—C —COOH I H glycine CH3 I H2N—C —COOH I H alanine 4 Types of Amino Acids Nonpolar R = H, CH3, alkyl groups, aromatic O Polar ll R = –CH2OH, –CH2SH, –CH2C–NH2, (polar groups with –O-, -SH, -N-) Polar/Acidic R = –CH2COOH, or -COOH Polar/ Basic R = –CH2CH2NH2 5 Essential Amino Acids • 10 amino acids not synthesized by the body • arg, his, ile, leu, lys, met, phe, thr, trp, val • Must obtain from the diet • All in diary products • 1 or more missing in grains and vegetables 6 Amino Acids as Acids and Bases • Ionization of the –NH2 and the –COOH group • Zwitterion has both a + and – charge • Zwitterion is neutral overall + NH2–CH2–COOH glycine H3N–CH2–COO– Zwitterion of glycine 7 pH and ionization OH– H+ + + H3N–CH2–COOH H3N–CH2–COO– H2N–CH2–COO– Positive ion zwitterion Negative ion Low pH neutral pH High pH 8 The Peptide Bond Amide bond formed by the –COOH of an amino acid and the –NH2 of the next amino acid + O || CH3 + | NH3–CH2–COH O + || H3N–CH–COO– + CH3 | NH3–CH2–C – N–CH–COO– | H peptide bond 9 Peptides • Amino acids linked by amide (peptide) bonds Gly H2Nend Lys Phe Peptide bonds Arg Ser -COOH end Glycyllysylphenylalanylarginylserine 10 Amino Acids, Proteins, and Enzymes Primary and Secondary Structure Tertiary and Quaternary Structure Protein Hydrolysis and Denaturation 11 Primary Structure of Proteins The particular sequence of amino acids that is the backbone of a peptide chain or protein CH3 CH3 CH3 O + S CH CH3 SH CH2 CH O CH2 O CH2 O - H3N CH C N CH C N CH C N CH C O H H Ala-Leu-Cys-Met H 12 Secondary Structure – Alpha Helix • Three-dimensional arrangement of amino acids with the polypeptide chain in a corkscrew shape • Held by H bonds between the H of –N-H group and the –O of C=O of the fourth amino acid along the chain • Looks like a coiled “telephone cord” 13 Secondary Structure – Beta Pleated Sheet • Polypeptide chains are arranged side by side • Hydrogen bonds form between chains • R groups of extend above and below the sheet • Typical of fibrous proteins such as silk 14 Secondary Structure – Triple Helix • Three polypeptide chains woven together • Glycine, proline, hydroxy proline and hydroxylysine • H bonding between –OH groups gives a strong structure • Typical of collagen, connective tissue, skin, tendons, and cartilage 15 Tertiary Structure • Specific overall shape of a protein • Cross links between R groups of amino acids in chain disulfide –S–S– + ionic –COO– H3N– H bonds C=O HO– hydrophobic –CH3 H3C– 16 Globular and Fibrous Proteins Globular proteins “spherical” shape Insulin Hemoglobin Enzymes Antibodies Fibrous proteins long, thin fibers Hair Wool Skin Nails 17 Quaternary Structure • Proteins with two or more chains • Example is hemoglobin Carries oxygen in blood Four polypeptide chains Each chain has a heme group to bind oxygen 18 Protein Hydrolysis • Break down of peptide bonds • Requires acid or base, water and heat • Gives smaller peptides and amino acids • Similar to digestion of proteins using enzymes • Occurs in cells to provide amino acids to synthesize other proteins and tissues 19 Hydrolysis of a Dipeptide OH CH3 O CH2 O + H3N CH C N CH C OH H2O, H + heat H OH CH2 O CH3 O + H3N CH COH + + H3N CH C OH 20 Denaturation Disruption of secondary, tertiary and quaternary protein structure by heat/organics Break apart H bonds and disrupt hydrophobic attractions acids/ bases Break H bonds between polar R groups and ionic bonds heavy metal ions React with S-S bonds to form solids agitation 21 Stretches chains until bonds break Secondary Structure – Triple Helix • Three polypeptide chains woven together • Glycine, proline, hydroxy proline and hydroxylysine • H bonding between –OH groups gives a strong structure • Typical of collagen, connective tissue, skin, tendons, and cartilage 22 Applications of Denaturation • Hard boiling an egg • Wiping the skin with alcohol swab for injection • Cooking food to destroy E. coli. • Heat used to cauterize blood vessels • Autoclave sterilizes instruments • Milk is heated to make yogurt 23 Functions of Proteins • • • • • • • • Structure – collagen, keratin,elastin Enzyme – lysozyme, amylase, Transport – hemoglobin, lipoproteins Contractile – actin, myosin, tubulin Hormone – insulin, growth hormone Antibody – IgG, Pigment – melanin, rhodopsin Recognition – CD4, MHC proteins 24