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Chapter 6: Basic Concepts of Enzyme Action. Proteolytic Enzymes Catalyze Peptide Bond Hydrolysis. Jellyfish luminescence. Gibb’s Free Energy Indicates Reaction Spontaneity . A → C. ∆G = ∆H - T∆S. ∆G°ʹ = ∆H°ʹ - T∆S°ʹ. ∆G = ∆G°ʹ + RTlnK eq.
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Chapter 6: Basic Concepts of Enzyme Action Proteolytic Enzymes Catalyze Peptide Bond Hydrolysis Jellyfish luminescence
Gibb’s Free Energy Indicates Reaction Spontaneity A → C ∆G = ∆H - T∆S ∆G°ʹ = ∆H°ʹ - T∆S°ʹ ∆G = ∆G°ʹ + RTlnKeq What determines if a reaction is spontaneous in the forward direction reverse direction or at equilibrium?
Entropy (∆S) is a measure of Disorder Lower Entropy Higher Entropy Enthalpy (∆H) is a measure of Heat Content Negative ∆H → Exothermic reaction Positive ∆H → Endothermic reaction What is ∆G, ∆H and ∆S for: Burning paper? Dissolving (NH4)2SO4 in H2O?
Enzymes Accelerate the Reaction Rate What catalysis difference can an enzyme make?
Enzymes Enhance Reaction Rates How are enhanced reaction rates possible?
Enzymes Decrease the Activation Energy How can enzymes lower the transition state? Is external energy required?
Mechanisms of Enzyme Catalysis • Acid-Base Catalysis • Covalent Catalysis • Metal Ion Catalysis • Orientation/Proximity Effects • Preferential Transition- State Binding Can the mechanism for an enzyme catalyzed versus uncatalyzed reaction be different?
Substrate Specificity Observed with each Proteolytic Enzyme • Papain cleave peptides non-selectively • Trypsin cleaves carboxyl side of bulky + charged R- groups • Chymotrypsin cleaves carboxyl side of bulky aromatic R-groups Thrombin
Enzyme-Substrate Binding Critical for Catalysis Lock and Key Model • Enzyme Active Site • 3-D cleft or crevice • Small part of enzyme • Unique micro-environment • Substrate binding by weak forces Induced Fit Model
Inhibition by Transition State Analogs Pyrrolidine the natural substrate binds 160 less tightly than pyrrole a transition state analog. What is the favored enzyme binding geometry?
Components that Facilitate Enzyme Catalysis What is the cofactor in ATP hydrolysis? What is the co-substrate in an oxidation-reduction reaction? What is a apoenzyme versus a holoenzyme?
Rate of Enzyme Catalysis Explain why enzyme activity increases with temperature and then precipitously drops off
RNAas A Digestive Enzyme Cleaving Mechanism Why does ribonuclease catalyzes the hydrolysis of RNA but not DNA
Conversion of Adenosine to Inosine What does the much greater binding affinity of 1,6-dihydropurine ribonucleoside than the substrate indicate about the enzyme mechanism?
