1. Enzyme Structure and Function AP Bio Lecture 3 Part 1

2. Proteins Foundation of nearly every dynamic function in an organism Account for +50% of dry mass Made of C, H, O, N, and some S Incredibly diverse and highly specific – Humans  Tens of thousands, each with different structure and function

3. Proteins Most enzymes are proteins  Without enzymes, life could not exists! – Enzymes = catalysts; speed up chemical reactions without being used up in the reaction “Workhorses” that keep cells running Names typically end in “-ase”

4. What kind of reaction is this? How do you know??

5. Activation Energy Chemical reactions involve bond breaking and bond forming

6. Activation Energy Chemical reactions involve bond breaking and bond forming – Instability occurs as the molecule is contorted into a new shape/form – Much energy is required to cause bonds to change – Example: Key ring (bending apart)

7. Activation Energy Chemical reactions involve bond breaking and bond forming – Instability occurs as the molecule is contorted into a new shape/form – Much energy is required to cause bonds to change – Example: Key ring (bending apart) Activation Energy: – Initial investment of energy needed to start a reaction – AKA free energy of activation (E A ) – Pushes reactants to the transition state (summit)

9. What does it mean to say this is an exergonic reaction?

10. How do enzymes change this? Is heat enough? Is heat appropriate?

11. Role of Enzymes in Reactions Proteins, DNA, and other complex molecules are high in free energy  This means they could readily breakdown! Why don’t they?? High activation energy acts as a barrier (this is a good thing!) But…what about when we NEED those molecules to break down?

12. Turn up the HEAT? Input of heat energy into a reaction would be sufficient to increase the rate of that reaction, but is this really the best solution? Why might heat not be the best idea for biological systems?

13. Turn up the HEAT? Input of heat energy into a reaction would be sufficient to increase the rate of that reaction, but is this really the best solution? High temperatures denature proteins (loss of structure = loss of function) Heat would speed up ALL reactions, not just the target ones

14. Enzyme Function Lower the activation energy (E A ) Allow reactant molecules to absorb enough energy to reach transition state at moderate temps Note: Enzymes do NOT change whether a reaction is endergonic or exergonic – only the rate at which an natural reaction would occur

16. Enzyme Structure Highly specific for each chemical reaction – Therefore they determine which chemical processes occur at any given time within the cell Enzyme-Substrate Complex

18. What happens in terms of activation energy when this complex forms?

19. Enzyme Substrate Complex Enzyme can recognize specific substrate even in presence of isomers Specificity results from protein shape (and complexity) Only a restricted region of the enzyme binds to the substrate  Active Site (location when catalysis occurs)

20. Slight shape changes  As substrate enters, interactions between R groups of enzyme and chemical groups of substrate lead to a snug fit (like a hand shake)

21. Catalysis at Active Site Substrate held in place with weak bonds – Hydrogen and ionic bonds Conversion of substrate to product – Catalyzed by the R groups of the enzyme

22. Catalysis at Active Site Products depart from active site Enzyme is free to take on more substrate Incredibly fast rate – Typical enzyme acts on 1000 substrate molecules per second! – Do you need a lot of enzyme? Why?

23. Enzymatic Process Enzymes can catalyze either forward or reverse reaction – Most metabolic reactions are reversible – Enzymes work on the reactions with negative ΔG (change in free energy) Several mechanisms…

24. Mechanisms for Enzyme Function (1) Template for two or more reactants to come together in proper orientation for a fusing reaction (2) Induced fit  Stretches substrate molecules toward transition state (instability) – EA is proportional to difficulty of breaking bonds – Distorting helps weaken bonds

25. Mechanisms for Enzyme Function (3) Active site provides microenvironment for reaction – More conducive to that reaction than the surrounding solution (4) Direct participation of the active site – Can involve brief covalent bonding between enzyme and substrate – Always reverses to put enzyme back to original state

26. Impacts on Initial Rate of Reaction Substrate concentration relative to enzyme – Too much leads to saturation (increase of substrate no longer matters) So …what ultimately limits the reaction?

27. Impacts on Initial Rate of Reaction Substrate concentration relative to enzyme – Too much leads to saturation (increase of substrate no longer matters) So …what ultimately limits the reaction? Speed at which the active site converts the substrate to product! Amount of enzyme Feedback loops  Produce more enzyme when low levels are detected