Chapter 3 Protein Structure and Function What Are the Building Blocks of Proteins In general physical and chemical processes proceed in the direction that results in potential energy and disorder How Can You Determine if a Reaction Will Be Spontaneous Gibbs Free Energy Change G G H T S Where T temperature in degree Kevin Where H is the difference in potential energy between products and reactants and is called enthalpy Where S is the change in entropy Reactions tend to be spontaneous if there is a net increase in entropy for the universe S is a large positive or if the products have lower potential energy than the reactants H is a large negative G 0 is an exergonic G 0 is an endergonic reaction that requires energy input G 0 is reaction that is at Temperature and Concentration Affect Reactions Breaking and forming bonds depends of collisions between molecules This allows electrons to interact The rate of a reaction depends The number of collisions depends on the temperature and the concentration of the reactants Higher temperature more collisions Higher concentration more collisions Acids and Bases Substances that give up hydrogen ions protons H ions are called HCl H2O H3O Cl Molecules that acquire protons and lower the hydrogen ion concentration of water are called NaOH Na OHOH H3O 2 H2O The Importance of Carbon Except for water almost all of the molecules found in organisms contain because it is the most versatile atom on earth Due to four valence electrons it can form many with different combinations and molecular shapes The Structure of Amino Acids All proteins are made from just amino acid building blocks All amino acids have a central carbon atom that bonds to things The Structure of Amino Acids In water pH 7 the and ionize to NH3 and COO respectively this helps amino acids stay in solution and makes them more reactive The Nature of Side Chains The differ only in the unique R group attached to the central carbon The properties of amino acids vary because their R groups vary Functional Groups Affect Reactivity R groups differ in their size shape reactivity and interactions with water 1 Nonpolar R groups do not form hydrogen bonds coalesce in water 2 Polar R groups form hydrogen bonds readily dissolve in water Amino acids with hydroxyl amino carboxyl or sulfhydryl functional groups in their side chains are more chemically reactive than those with side chains composed of only carbon and hydrogen atoms The nature of the R group affects how soluble the amino acid is in water Are the amino acids soluble in water The nature of the R group affects how soluble the amino acid is in water Are the amino acids soluble in water The nature of the R group affects how soluble the amino acid is in water Are the amino acids soluble in water How Do Amino Acids Link to Form Proteins The polarity of R groups determines interactions with water How Do Amino Acids Link to Form Proteins Polymerization Polymer one or more monomers one part bound together Thus amino acids polymerize to form A macromolecule is a very large molecule that is made up of smaller molecules joined together Definitions Check knowledge Monomer Polymer Polymerization Macromolecule What is a protein The Peptide Bond Condensation reactions bond the carboxyl group of one amino acid to the amino group of another to form a A chain of amino acids linked by peptide bonds is called a Polypeptides containing fewer than 50 amino acids are called oligopeptides peptides Polypeptides containing more than 50 amino acids are called proteins Building Proteins Polymerization is not spontaneous needs input of energy Within the polypeptide the peptide bonds form a backbone with three key characteristics 1 Side chains can interact with each other or water 2 Free amino group on the left is called the N terminus Free carboxyl group on the right is called the C terminus 3 Single bonds on either side of the peptide bond can rotate making the entire structure flexible
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