Lecture Presentation Chapter 19 Amino Acids and Proteins Karen C Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 19 Amino Acids and Proteins • Radiology technicians work with radiologists to produce images that allow for the diagnosis and treatment of certain medical conditions • Technicians operate imaging equipment such as X-ray, computed tomography (CT), and positron emission tomography (PET) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 19 Readiness Key Math Skill • Calculating pH from [H3O+] (11.6) Core Chemistry Skills • Writing Equations for Reactions of Acids and Bases (11.7) • Naming Carboxylic Acids (16.1) • Forming Amides (18.5) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 19.1 Proteins and Amino Acids Protein molecules, compared with many of the compounds we have studied, can be gigantic The horns of animals are made of proteins Learning Goal Classify proteins by their functions Give the name and abbreviations for an amino acid, and draw its zwitterion General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Functions of Proteins Proteins • in the body are polymers made from 20 different amino acids • differ in characteristics and functions that depend on the order of amino acids that make up the protein • form structural components such as cartilage, muscles, hair, and nails • function as enzymes to regulate biological reactions such as digestion and cellular metabolism • including hemoglobin and myoglobin transport oxygen in the blood General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Structural Classification of Proteins and Functions General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Amino Acids Amino acids, the molecular building blocks of proteins, have a central carbon atom called the α carbon, bonded to • two functional groups: an ammonium group (— NH3+) and a carboxylate group (— COO−) • a hydrogen atom and an R group or side chain in addition to the carboxylate and ammonium groups General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Zwitterions At physiological pH, the • ionized ammonium and carboxylate groups give an amino acid a balance of positive and negative charge, which gives an overall zero charge • neutral amino acid, which is called a zwitterion, occurs at a specific pH value known as its isoelectric point (pI) Core Chemistry Skill Drawing the Zwitterion for an Amino Acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Classification of Amino Acids Amino acids are classified using their specific R groups The • nonpolar (hydrophobic) amino acids have hydrogen, alkyl, or aromatic R groups • polar amino acids have R groups that interact with water, which makes them hydrophilic • polar neutral amino acids contain an hydroxyl (— OH), a thiol (— SH), or an amide (— CONH2) R group • polar acidic amino acids contain a carboxylate (— COO−) R group • polar basic amino acids contain an ammonium (— NH3+) R group General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Classification of Amino Acids A summary of amino acid types and their interactions with water General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chemistry Link to Health: Sickle Cell Anemia Sickle cell anemia is caused by an abnormality in the shape of one of the subunits of the hemoglobin protein • The sixth amino acid in the β-chain, polar acidic glutamic acid, is replaced by valine, a nonpolar amino acid • The nonpolar R group on valine is attracted to the nonpolar regions within the beta hemoglobin chains • The red blood cells change from a rounded shape to a crescent shape, like that of a sickle, which interferes with their ability to transport enough oxygen General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chemistry Link to Health: Sickle Cell Anemia Hydrophobic interactions also cause sickle cell hemoglobin molecules to stick together They form insoluble fibers of sickle cell hemoglobin that • clog capillaries • cause inflammation, pain, and organ damage • cause low oxygen levels in the affected tissues General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc 19.6 Protein Hydrolysis and Denaturation Denaturation of a protein occurs when the interactions of residues that stabilize tertiary or quaternary structures are disrupted, which destroys the shape and renders the protein biologically inactive Learning Goal Describe the hydrolysis and denaturation of proteins General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Protein Hydrolysis Peptide bonds are broken through hydrolysis reactions Hydrolysis • occurs in the stomach when enzymes catalyze the hydrolysis of proteins to give amino acids • breaks up the primary structure by breaking the covalent peptide bonds that link the amino acids General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Protein Hydrolysis General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins Denaturation of a protein • occurs when a change disrupts the interactions between residues that stabilize the secondary, tertiary, or quaternary structure • does not affect the amide bonds between amino acids General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins The loss of secondary and tertiary structures in a protein occurs when conditions change, such as • increasing the temperature • making the pH very acidic or basic • adding certain organic compounds or heavy metal ions • adding mechanical agitation When the interactions between the residues are disrupted, • a globular protein unfolds • the tertiary structure is disrupted and the protein is no longer biologically active General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins, Heat Proteins are denatured when heated above 50 °C The heat • disrupts the hydrogen bonds and hydrophobic interactions between nonpolar residues • does not change the nutritional value of proteins but makes them more digestible High temperatures are also used to disinfect surgical instruments and gowns by denaturing the proteins of any bacteria present General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins, Acids and Bases Proteins can be denatured by changing the pH, which • breaks hydrogen bonds • disrupts ionic bonds and salt bridges Tannic acid, a weak acid used in burn ointments, is applied to the site of the burn to coagulate proteins It forms a protective cover and prevents further loss of fluid from the burn General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins, Organic Compounds Organic compounds such as ethanol and isopropyl alcohol act as disinfectants by • exchanging the bacterial protein’s hydrogen bonds to water with their own • disrupting the side chain intramolecular hydrogen bonding An alcohol swab is used to clean wounds or to prepare the skin for an injection because the alcohol passes through the cell walls and coagulates the proteins inside the bacteria General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins, Heavy Metal Ions Heavy metal ions such as Ag+, Pb2+, and Hg2+ denature proteins by forming bonds with ionic residues or reacting with disulfide — S — S — bonds Dilute (1%) solutions of AgNO3 are placed in the eyes of newborn babies to destroy the bacteria that cause gonorrhea General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins, Agitation The whipping of cream and the beating of egg whites are examples of using mechanical agitation to denature proteins The whipping action stretches the polypeptide chains until the stabilizing interactions are disrupted General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Denaturation of Proteins, Summary General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Concept Map General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc ... Amides (18 .5) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2 016 Pearson Education, Inc 19 . 1 Proteins and Amino Acids Protein molecules, compared with... Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2 016 Pearson Education, Inc Ionized Forms of Amino Acids General, Organic, and Biological Chemistry: Structures of Life, 5/e... Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2 016 Pearson Education, Inc General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2 016 Pearson Education,