Enzymes: “ Helper ” Protein molecules

1. Enzymes:“Helper” Protein molecules

2. Enzymes • Catalysts for biological reactions • Most are proteins • Lower the activation energy • Increase the rate of reaction • Activity lost if denatured • May be simple proteins • May contain cofactors such as metal ions or organic (vitamins)

3. Flow of energy through life Life is built on chemical reactions

4. + + Chemical reactions of life • Processes of life • building molecules • synthesis • breaking down molecules • digestion

5. enzyme + enzyme + Nothing works without enzymes! • How important are enzymes? • all chemical reactions in living organisms require enzymes to work • building molecules • synthesis enzymes • breaking down molecules • digestive enzymes • enzymes speed up reactions • “catalysts” We can’t live without enzymes!

6. CATALYST – A SUBSTANCE THAT CAUSES A CHEMICAL REACTION TO HAPPEN MORE QUICKLY. Enzymes work by weakening bonds which lowers activation energy

7. Without Enzyme With Enzyme Free Energy Free energy of activation Reactants Products Progress of the reaction Enzymes

8. Enzymes are proteins • Each enzyme is the specific helper to a specific reaction • each enzyme needs to be the right shape for the job • enzymes are named for the reaction they help • sucrase breaks down sucrose • proteases breakdown proteins • lipases breakdown lipids • DNA polymerase builds DNA

9. active site Enzymes aren’t used up • Enzymes are not changed by the reaction • used only temporarily • re-used again for the same reaction with other molecules • very little enzyme needed to help in many reactions substrate product enzyme

10. Enzyme vocabulary • Enzyme • helper protein molecule; catalyst • Substrate • molecule that enzymes work on • Products • what the enzyme helps produce from the reaction • Active site • part of enzyme that substrate molecule fits into

11. It’s shape that matters! • Lock & Key model • shape of protein allows enzyme & substrate to fit • specific enzyme for each specific reaction

12. Lock and Key Model + + E + S ES complex E + P P S S P

13. 2 1 3

14. Enzyme Action: Induced Fit Model • Enzyme structure flexible, not rigid • Enzyme and active site adjust shape to bind substrate • Increases range of substrate specificity • Shape changes also improve catalysis during reaction

15. Enzyme Action: Induced Fit Model • E + S ES complex E + P P S S S P

16. Factors Affecting Enzyme Action: Temperature • Little activity at low temperature • Rate increases with temperature • Most active at optimum temperatures (usually 37°C in humans) • Activity lost with denaturation at high temperatures

17. Factors Affecting Enzyme Action Optimum temperature Reaction Rate Low High Temperature

18. What affects enzyme action • Correct protein structure • correct order of amino acids • why? enzyme has to be right shape • Temperature • why? enzyme has to be right shape • pH (acids & bases) • why? enzyme has to be right shape

19. Order of amino acids • Wrong order = wrong shape = can’t do its job! foldedprotein chain ofamino acids DNA right shape! foldedprotein chain ofamino acids wrong shape! DNA

20. Factors Affecting Enzyme Action:Substrate Concentration • Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) • Maximum activity reached when all of enzyme combines with substrate

21. Factors Affecting Enzyme Action Maximum activity Reaction Rate substrate concentration

22. Temperature • Effect on rates of enzyme activity • Optimum temperature • greatest number of collisions between enzyme & substrate • human enzymes • 35°- 40°C (body temp = 37°C) • Raise temperature (boiling) • denature protein = unfold = lose shape • Lower temperature T° • molecules move slower • fewer collisions between enzyme & substrate

23. 37° Temperature humanenzymes reaction rate temperature

24. How do cold-blooded creatures do it?

25. pH • Effect on rates of enzyme activity • changes in pH changes protein shape • most human enzymes = pH 6-8 • depends on where in body • pepsin (stomach) = pH 3 • trypsin (small intestines) = pH 8

26. pH stomachpepsin intestinestrypsin What’s happening here?! reaction rate 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH

27. Enzyme Inhibition Inhibitors • cause a loss of catalytic activity • Change the protein structure of an enzyme • May be competitive or noncompetitive • Some effects are irreversible

28. Competitive Inhibition A competitive inhibitor • Has a structure similar to substrate • Occupies active site • Competes with substrate for active site • Has effect reversed by increasing substrate concentration

29. Noncompetitive Inhibition A noncompetitive inhibitor • Does not have a structure like substrate • Binds to the enzyme but not active site • Changes the shape of enzyme and active site • Substrate cannot fit altered active site • No reaction occurs • Effect is not reversed by adding substrate

31. Allosteric Site – undergoing a change in the shape and activity of a protein (as an enzyme) that results from the combination with another substance at a point other than the chemically active site.

32. SHAPE! For enzymes…What matters?