1. ENZYMES Energy and Enzymes Almost all energy for life is derived from the sun. Life requires energy. A “factoid” - The sun’s energy that strikes Earth each day is equivalent to one million Hiroshima-sized atomic bombs. Photosynthesis harnesses about 1% of that energy – 10,000 “atomic bomb equivalents” per day.

2. ENZYMES Chemistry and Life One unromantic yet productive way of viewing life is to see it as a set of coordinated chemical reactions. This leads to an obvious question – What determines what chemical reactions are possible?

3. ENZYMES Chemical Reactions Whether a chemical reaction will or won’t occur under particular conditions is determined by the laws of thermodynamics. If the overall amount of order is decreased by a reaction, the reaction is wanted. Keeping it simple - If the overall amount of order is increased by a reaction, the reaction is not wanted.

4. ENZYMES The Direction of Spontaneous Reactions (and what it takes to go the other way) Going this way is possible, but it requires the input of energy.

5. ENZYMES Life Requires Lots of Unfavorable Reactions – How Is This Possible? By coupling favorable, energy- releasing reactions to unfavorable, energy- requiring reactions. favorable reactions unfavorable reactions

6. ENZYMES The “Nature of Life” – Coupling Favorable, Energy - Yielding Reactions to Unfavorable, Energy-Requiring Reactions

7. ENZYMES Even When Cells Build Complex Molecules and Structures, the Second Law of Thermodynamics (Entropy or the “kids bedroom principle”) Isn’t Violated

8. ENZYMES ATP - Life’s Energy Currency Energy is released when ATP is hydrolyzed (broken down) to ADP. ATP is restored from ADP and an input of energy. ATP’s energy is used to drive endergonic (energy-requiring) reactions.

9. ENZYMES The Way ATP Often Works

10. ENZYMES Enzymes Speed Biochemical Reactions Enzymes are biological catalysts – substances that speed a reaction without being altered in the reaction. Most enzymes are proteins, some are RNA. Enzymes are essential for life. Model of the surface of an enzyme.

11. ENZYMES Enzymes Lower a Reaction’s Activation Energy

12. ENZYMES Enzyme Action

13. ENZYMES The Fit Between Enzyme and Substrate is Critical and Precise Hexokinase, an enzyme (blue), binding its substrate, glucose (yellow).

14. ENZYMES The active site of an enzyme is where substrate is bound. Many Enzymes Work by Altering the Shape of Their Substrates

15. ENZYMES The synthesis of biological molecules often requires many enzyme- catalyzed steps. The entire set of steps is a metabolic pathway. Metabolic Pathways

16. ENZYMES Enzyme Activity is Often Regulated Feedback inhibition - a common form of enzyme regulation in which the product inhibits the enzyme.

17. ENZYMES Enzymes allow chemical reactions to occur under tightly controlled conditions. Enzymes are catalysts in living things. –Enzymes are needed for almost all processes. –Most enzymes are proteins.

18. ENZYMES Proteins –Enzymes as Biological Catalysts -Increase reaction rates by over 1,000,000-fold -Two fundamental properties ·Increase the reaction rate with no alteration of the enzyme ·Increase the reaction rate without altering the equilibrium -Reduce the activation energy

19. ENZYMES Disruptions in homeostasis can prevent enzymes from functioning. –Enzymes function best in a small range of conditions. –Changes in temperature and pH can break hydrogen bonds. –An enzyme’s function depends on its structure.

20. ENZYMES An enzyme’s structure allows only certain reactants to bind to the enzyme. –substrates –active site substrates (reactants) enzyme Substrates bind to an enzyme at certain places called active sites.

21. ENZYMES Proteins –Enzymes as Biological Catalysts -Two popular models provide an aid to understanding the mechanisms of enzyme action: ·Lock-and-key ·Induced fit

22. ENZYMES The lock-and-key model helps illustrate how enzymes function. –substrates brought together –bonds in substrates weakened Substrates bind to an enzyme at certain places called active sites. The enzyme brings substrates together and weakens their bonds. The catalyzed reaction forms a product that is released from the enzyme.