Protein Structure and Enzyme Function

1. Protein Structure and Enzyme Function How Protein Activity Depends on Proper Folding

2. Four Levels of Protein Structure Tertiary(Folding by R-group interactions) Primary(Sequence) Quaternary(Two or more chains associating) Secondary(Coiling by Hydrogen Bonding)

3. Proteins: Structure • Primary structure = chain of amino acids • Amino acids have common features Carboxylic AcidGroup AminoGroup     R CentralCarbon The “R” GroupDiffers for Each Amino Acid

4. Proteins: StructureForming the Protein Chain Phenylalanine Leucine Dehydration Synthesis between COOH & NH2

5. Proteins: StructureForming the Protein Chain The Peptide Bond Water Phenylalanine-Leucine Dipeptide

7. Four Levels of Protein Structure • Secondary Structure: Folded structure due to hydrogen bonds between the amino and acid groups of amino acids N C N C H O H O or O H O H N C N C

9. Four Levels of Protein Structure • Tertiary Structure: Three dimensional folded structure due to attractions and repulsions between R groups Can involve covalent bonding hydrogen bonding ionic interactions hydrophilic and hydrophobic interactions

11. Four Levels of Protein Structure • Quaternary Structure: Association of two or more protein chains eg. Hemoglobin is composed of 4 protein chains 2 are called alpha hemoglobin 2 are called beta hemoglobin

12. Which structure results from hydrogen bonding? Which structure involves an association of two or more protein chains? Which structure describes the linear sequence of amino acids? Which structure depends upon interactions between the R groups of the amino acids? Primary Secondary Tertiary Quaternary Applying Your Knowledge

13. Enzymes Assist in Biological Reactions • Enzymes are biological catalysts. biological: composed of protein or, rarely, RNA catalyst: speeds up a reaction without being changed by the reaction

14. Properties of Enzymes • Most enzymes are proteins. • All enzymes are SPECIFIC for the reactants (substrates) in the reactions that they catalyze. • Enzymes speed up biological reactions by lowering the activation energy for the reaction.

15. Enzyme-Substrate Interactions Substrate Substrate 1 Substrates enter active site ActiveSite 2 Shape change promotes reaction Enzyme Product released;enzyme ready again

16. high Energycontentofmolecules low Progress of reaction Activation Energy: Controls Rate of Reaction Activationenergy withoutcatalyst Activationenergy withcatalyst

17. Properties of Enzymes • Three dimensional structure of an enzyme preserves its ACTIVE SITE active site: region on enzyme where reactants bind • Conditions that can affect three dimensional structure include: heat, pH (acid/base balance) and other chemicals (salt, charged ions)

18. fewer collisions between enzyme and substrate enzyme unfolds enzyme unfolds Effects of Temperature and pH on Enzymatic Activity

19. A biological catalyst is a(n) __________ . The region on an enzyme where reactants bind is the _________. Enzymes (raise or lower) the (1, 2, 3 or 4) of a reaction. Active Site Activation Energy Enzyme Catalyst Applying Your Knowledge