Figure 8-01

1. Figure 8-01

2. This new material we begin today will be on exam #2 Material for exam #1 (March 4) will include these textbook chapters: Chapter 3-water Chapter 4-Carbon and the Molecular Diversity of Life (especially functional groups) Chapter 6-Cell Structure and Function Chapter 7-Cell Membranes

3. An Introduction to Metabolism I. Metabolism, Energy and Life • The chemistry of life is organized into metabolic pathways • Organisms transform energy • The energy transformations of life are subject to two laws of thermodynamics • Organisms live at the expense of free energy • ATP powers cellular work by coupling exergonic to endergonic reactions II. Enzymes • Enzymes speed up metabolic reactions by lowering energy barriers • Enzymes are substrate-specific • The active site is an enzyme’s catalytic center III. The Control of Metabolism • Metabolic control often demands allosteric regulation • The location of enzymes within a cell helps to order metabolism

4. Cell Energetics • Energy definition-capacity to do work. In terms of cell, what are some types of work that have to be done to stay alive?

5. Figure 6.2x1 Kinetic and potential energy: dam

6. Important forms of kinetic and potential energy for living organisms • Kinetic-sunlight; heat • Potential-chemical bond energy (glucose, ATP, etc.)

7. Cell Energetics are Governed by the Laws of Thermodynamics • First Law of Thermodynamics (law of Conservation of Energy) • Energy cannot be created or destroyed but it can be changed in form. • Energy transformation is permissible (life depends on this happening)-sunlightchemical

8. On the platform, the diver has more potential energy. Diving converts potential energy to kinetic energy. LE 8-2 Climbing up converts kinetic energy of muscle movement to potential energy. In the water, the diver has less potential energy.

9. Second Law of Thermodynamics • All matter tends to spontaneously move to the greatest possible state of stability (bonding) • All matter tends to spontaneously move from areas of higher concentration to lower concentration (diffusion) • All matter tends to spontaneously move from states of higher free energy (less stable, more concentrated) to states of lower free energy (more stable, less concentrated)

10. Entropy-Another way to look at the 2nd law of Thermodynamics • We’ve defined the 2nd law previously in terms of stability and free energy. • Another way is to understand the 2nd Law is to use the concept of entropy. • Entropy is the measure of the disorganization of a system • All systems spontaneously assume the state of greatest entropy.

11. Cells, entropy, and the 2nd Law of Thermodynamics • Cells are very organized (low entropy) • How can a cell exist in the face of the 2nd Law (maintain organization)? Expend energy. • It’s work to stay alive! • The key is that the cell decreases its entropy at the expense of increasing the entropy of its surroundings. • Cells take ordered (high energy molecules from the environment and return unordered waste products). • The cell is an open system (can exchange energy with its environment). • Can a closed system maintain a state of low entropy?

12. LE 8-3 CO2 Heat Chemical energy H2O First law of thermodynamics Second law of thermodynamics

13. What does the 2nd Law of Thermodynamics say about Life?

14. Life is improbable. • Life cannot violate the principle that entropy increases. • Living things live at the expense of their environment (living things are able to maintain a state of decreased entropy because the entropy of the entire universe (system + surroundings) is increasing • Life can only exist if energy is constantly being expended.

15. What form of energy does the cell use to maintain its organization? • ATP • ATP cycle

16. Adenine LE 8-8 Phosphate groups Ribose

17. P P P LE 8-9 Adenosine triphosphate (ATP) H2O + P P P + Energy i Adenosine diphosphate (ADP) Inorganic phosphate

18. ATP hydrolysis “releases” energy so that cellular work can be done • bond breaking versus bond formation

19. Why does ATP hydrolysis “release” energy?

20. ATP and cellular work • How does ATP hydrolysis power cellular work? • Phosphorylation and dephosphorylation of proteins

21. P i P Protein moved Motor protein Mechanical work: ATP phosphorylates motor proteins LE 8-11 Membrane protein ADP ATP + P i P P i Solute transported Solute Transport work: ATP phosphorylates transport proteins P NH2 NH3 P + + Glu i Glu Reactants: Glutamic acid and ammonia Product (glutamine) made Chemical work: ATP phosphorylates key reactants

22. How is ATP produced? • Cellular respiration (cash versus check analogy) • Difference in autotrophs and heterotrophs

23. LE 8-UN141 Enzyme 1 Enzyme 2 Enzyme 3 A B D C Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

24. Metabolism and Spontaneous reactions • Previously stated that catabolic reactions were spontaneous and anabolic were not spontaneous.

25. Metabolism • Cell respiration is one example of a metabolic pathway. The chemistry of life is organized into metabolic pathways (complex and regulated by enzymes). (street analogy). • 2 types of metabolic pathways • a. catabolic-degradative, energy releasing (downhill), oxidative, spontaneous • b. anabolic-synthetic, energy requiring (up hill), reduction, not spontaneous

26. Figure 6.1  The complexity of metabolism

27. Spontaneous reactions • What are they? • They happen on their own without an input of energy • They are a result of the 2nd law of Thermodynamics

28. LE 8-5 Gravitational motion Diffusion Chemical reaction

29. What determines spontaneity of a chemical reaction? • A +B  C+D (substrate products) • Spontaneous-decrease in free energy (downhill), not spontaneous-increase free energy (uphill) • What is free energy? Energy available to do work. G=H-TS • Maximum amount of free energy that can be harvested from a reaction is the free energy change of the reaction (D G). • DG=DH-T D S • D G-energy available to do work (keep cells alive) • D H-total energy • DS-energy unavailable to do work

30. How is D G determined for a reaction? FE of products –FE of reactants. • a. If D G is negative (the free energy of the reactants is > fe of products), the reaction is spontaneous (downhill). • b. If D G is positive (the fe of the reactants is < fe of products), the reaction is not spontaneous (uphill). • c. If D G is 0-no free energy difference. The reaction is at equilibrium. No work can be done from that reaction.

31. Figure 6.5 The relationship of free energy to stability, work capacity, and spontaneous change

32. Reactants Amount of energy released (G < 0) LE 8-6a Energy Free energy Products Progress of the reaction Exergonic reaction: energy released

33. Products LE 8-6b Amount of energy required (G > 0) Free energy Energy Reactants Progress of the reaction Endergonic reaction: energy required

34. Exergonic and Endergonic reactions • Reactions can also be classified based on free energy changes. Endergonic and exergonic reactions.

35. Differences in Exergonic and Endergonic Reactions

36. Metabolic reactions and equilibrium • What would be the problem for a cell if its metabolic reactions (especially catabolic ones) were allowed to reach equilibrium? • Cellular metabolism is normally not allowed to reach equilibrium. • Metabolism generally involves multi-step pathways where the product of one reaction becomes the substrate of the next reaction. • This strategy only works because cells are open systems

37. G < 0 G = 0 LE 8-7a A closed hydroelectric system

38. G < 0 LE 8-7b An open hydroelectric system

39. G < 0 G < 0 LE 8-7c G < 0 A multistep open hydroelectric system

40. Relationship between catabolic and anabolic reactions • Coupling endergonic and exergonic reactions • example.

41. ATP LE 8-12 Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy- yielding processes) P ADP + i

42. Endergonic reaction: DG is positive, reaction is not spontaneous NH2 NH3 DG = +3.4 kcal/mol + Glu Glu LE 8-10 Ammonia Glutamine Glutamic acid Exergonic reaction: DG is negative, reaction is spontaneous P ATP ADP DG = –7.3 kcal/mol H2O + + i Coupled reactions: Overall DG is negative; together, reactions are spontaneous DG = –3.9 kcal/mol

43. LE 8-13 Sucrose C12H22O11 Glucose C6H12O6 Fructose C6H12O6

44. Enzymes • Characteristics

45. Substrates enter active site; enzyme changes shape so its active site embraces the substrates (induced fit). Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. • Active site (and R groups of • its amino acids) can lower EA • and speed up a reaction by • acting as a template for • substrate orientation, • stressing the substrates • and stabilizing the • transition state, • providing a favorable • microenvironment, • participating directly in the • catalytic reaction. Substrates LE 8-17 Enzyme-substrate complex Active site is available for two new substrate molecules. Enzyme Products are released. Substrates are converted into products. Products

46. Substrate LE 8-16 Active site Enzyme-substrate complex Enzyme

47. Catalysis • Properties of a catalyst • How do enzymes increase the rate of a chemical reaction • Why don’t enzymes alter the D of a reaction?

48. B A C D Transition state LE 8-14 EA B A Free energy D C Reactants B A DG < O C D Products Progress of the reaction

49. Course of reaction without enzyme EA without enzyme EA with enzyme is lower LE 8-15 Reactants Free energy Course of reaction with enzyme DG is unaffected by enzyme Products Progress of the reaction

50. Factors influencing enzyme activity