Chapter 8 An Introduction to Energy & Metabolism

1. Chapter 8 An Introduction to Energy & Metabolism Topics: • Thermodynamic Laws • Catabolism & Anabolism (metabolism) • Exergonic vs. Endergonic Reactions • Free Energy • ATP Cycle & Energy Coupling • Enzyme (structure & function)

2. Main Topics to Cover-Ch. 8 • Potential vs. Kinetic Energy • First Two Laws of Thermodynamics • Entropy, Enthalpy, and Free Energy • Endergonic vs. Exergonic Reactions • Anabolism & Catabolism = Metabolism • Energy Coupling: Oxidation/Reduction • ATP; Structure & Function • Enzymes Structure & Function- allosteric, feedback mechanisms

3. Energy is the capacity to perform work • Energy is defined as the capacity to do work • All organisms require energy to stay alive • Energy makes change possible

4. ENERGY AND THE CELL • Living cells are compartmentalized by membranes • Membranes are sites where chemical reactions can occur in an orderly manner • Living cells process energy by means of enzyme-controlled chemical reactions

5. Kinetic energy is energy that is actually doing work Figure 5.1A • Potential energy is stored energy Figure 5.1B

6. Thermodynamics • Energy (E)~ capacity to do work; Kinetic energy~ energy of motion; Potential energy~ stored energy • Thermodynamics~ study of E transformations • 1st Law: conservation of energy; E transferred/transformed, not created/destroyed • 2nd Law: transformations increase entropy (disorder, randomness) • Combo: quantity of E is constant, quality is not

7. Two laws govern energy conversion • First law of thermodynamics • Energy can be changed from one form to another • However, energy cannot be created or destroyed Figure 5.2A

8. Energy changes are not 100% efficient • Energy conversions increase disorder, or entropy • Some energy is always lost as heat • Second law of thermodynamics Figure 5.2B

9. Groups of 2 on computers: • Do this interactive on Wiley ‘Interactions in Biochemistry’ website. Do all 3 quizzes. • https://www.wiley.com/college/boyer/0470003790/reviews/kinetics/kinetics_stability.htm

10. Metabolism/Bioenergetics • Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell • Catabolic pathways: degradative process such as cellular respiration; releases energy • Anabolic pathways: building process such as protein synthesis; photosynthesis; consumes energy

11. Equation Used to Determine Free Energy of a System G = H - T S G: Quantity of Free Energy H: Enthalpy = System’s Total Energy (chemical Bond energy) T: Temperature (absolute temp. in Kelvin units) S: Entropy = Disorder of the system Spontaneous Reaction = G will be negative (energy is released ie. Exergonic.) Non spontaneous Reaction (Endergonic) G will be positive. What happens when G is ZERO ???

13. Free Energy • Free energy: portion of system’s E that can perform work (at a constant T) • Exergonic reaction: net release of free E to surroundings (products have less free energy than reactants) • Endergonic reaction: absorbs free E from surroundings • (products have more free energy than reactants)

14. ATP & Energy Coupling See Pgs. 149-151

15. ATP shuttles chemical energy within the cell • ATP is thought as the energy “currency” of a cell • In cellular respiration, some energy is stored in ATP molecules • ATP powers nearly all forms of cellular work • ATP molecules are the key to energy coupling

16. General Facts about ATP • Human use about 99 lbs of ATP each day @rest • Every second 10 million ATP’s are made from ADP • Bacteria has about a one-second supply of ATP

17. Energy Coupling & ATP • Energy coupling: use of exergonic process to drive an endergonic one (ATP). Ex: Respiration (hydrolysis of glucose) is overall exergonic and will result in synthesizing ATP from ADP+P, which is endergonic • Adenosine triphosphate (nucleotide w/3 PO4’s) • ATP tail: high negative charge • ATP hydrolysis: release of free Energy • Phosphorylation: binding of the released phosphate to another molecule

18. Introductory Questions #6 • Explain how potential energy is different from kinetic energy. 2) Define each variable in the equation: ∆G = ∆H – T ∆S 3) What is the difference between an exergonic reaction and an endergonic reaction? • How is ATP associated with coupled reactions? What purpose does it serve? • How is an electron carried from one molecule to the next? Name a molecule that can carry an electron.

19. The Hydrolysis of ATP

20. When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction supplies energy for cellular work. G = -32 KJ/mol (-7.6 Kcal/mol) Adenine Phosphategroups Hydrolysis Energy Ribose Adenosine triphosphate Adenosine diphosphate(ADP) Figure 5.4A

21. The ATP cycle Hydrolysis Dehydration synthesis Energy from exergonic reactions Energy for endergonic reactions Figure 5.4C

22. Example of Energy Coupling w/ATP • Forming the Disaccharide Sucrose involves: glucose + fructose → sucrose (G = +27 KJ/mol) ENDERGONIC Reaction Couple w/hydrolysis of ATP (G = - 32KJ/mol) Occurs in a couple of reaction steps: Reaction#1: Glucose + ATP → glucose-P + ADP **glucose has been phosphorylated **ATP has been hydolyzed Reaction #2: Glucose-P + fructose → Sucrose + Pi (Pi is a low energy inorganic phosphate)

23. How ATP powers cellular work Reactants Products Work Potential energy of molecules Protein Figure 5.4B

24. Three Functions of ATP

25. Enzymes: Structure & Function Watch: Bozeman Video; Study Ch 8 (last part)

26. Enzymes speed up the cell’s chemical reactions by lowering energy barriers • For a chemical reaction to begin, reactants must absorb some energy • This energy is called the energy of activation (EA) • This represents the energy barrier that prevents molecules from breaking down spontaneously

27. Enzymes • Catalytic proteins: change the rate of reactions w/o being consumed • Free E of activation (activation E): the E required to break bonds • Substrate: enzyme reactant • Active site: pocket or groove on enzyme that binds to substrate • Induced fit model

28. A protein catalyst called an enzyme can decrease the energy barrier EA barrier Enzyme Reactants 1 Products 2 Figure 5.5A

29. Enzymes Catalyze Cellular Reactions • Enzymes are recyclable and not used up in catalyzing reactions with substrates • Enzymes are selective and substrate specific • This selectivity determines which chemical reactions occur in a cell

30. How an Enzyme Works- Exp: Sucrase

31. The Cellular Environment affects Enzyme Activity • Enzyme activity is influenced by • temperature • salt concentration • pH • All of these can denature enzymes if not within optimal ranges • Cofactors: inorganic, nonprotein ‘helpers’ (stabilizers) • ex.: zinc, iron, copper • Coenzymes: organic helpers - ex. vitamins

32. Effects on Enzyme Activity • Temperature • pH

33. Enzyme Inhibitors • Competitive: competes for active site (reversible); mimics the substrate • Noncompetitive: bind to another part of enzyme (allosteric site) altering its conformation (shape); poisons, many antibiotics • Irreversible (covalent); reversible (weaker bonds. ex- H bonds)

34. Enzyme inhibitors block enzyme action • Inhibitors interfere with enzymes • A competitive inhibitor takes the place of a substrate in the active site • A noncompetitive inhibitor alters an enzyme’s function by changing its shape Substrate Active site Enzyme NORMAL BINDING OF SUBSTRATE Competitiveinhibitor Noncompetitiveinhibitor ENZYME INHIBITION Figure 5.8

35. Competitive & Noncompetitive Inhibitors

36. Some Pesticides and Antibiotics inhibit Enzymes • Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system • Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria • Penicillin inhibits an enzyme that bacteria use in making cell walls

37. Enzyme Regulation- *open book to p. 156-158 (8th ed) • 1- Allosteric Regulation: ‘Simplified’ diagram

38. Allosteric Regulation: Activators & Inhibitors • 1-

39. Cooperativity Regulation • 2-

40. Feedback Inhibition

41. Negative Feedback Inhibition • ‘Sufficient’ concentration of a product can inhibit an enzyme in the pathway to stop production • Exp- Isoleucine (previous slide) • non-essential amino acid. This means cells can synthesize it if insufficient quantities are in the diet. *FYI- ~half of the 20 aa are non-essential. What’s an essential aa?

42. Enzymes- Watch these • http://www.ekcsk12.org/science/aplabreview/lab02.htm **Description of Enzyme Lab • Lab Simulation: http://bioweb.wku.edu/courses/Biol114/enzyme/enzyme1.asp

43. Introductory Questions-1 (only # 2 is on Unit 2 test) • Explain how potential energy is different from kinetic energy. What are some ways we can measure energy? 2) Define each variable in the equation: ∆G = ∆H – T ∆S 3) What is the difference between an exergonic reaction and an endergonic reaction? • How is ATP associated with coupled reactions? What purpose does it serve? • How is an electron carried from one molecule to the next? Name a molecule that can carry an electron.

44. Introductory Questions- 2 (know all for Unit 2 test) • Name three ways that enzyme activity can be measured as mentioned in your lab guidesheet. • Explain how the reactivity of pepsin is different from trypsin. (Fig. 8.17) • Give an two examples of cofactors and two examples of conenzymes. How are they different? Alike? • How is a competitive inhibitor different from a non-competitive inhibitor? • What is an allosteric regulation? • Distinguish between pos & neg feedback control