Essential Concepts of Metabolism

1. Essential Concepts of Metabolism Chapter 5 Microbiology 130

2. Metabolism: An Overview • Metabolism- • Anabolism • Catabolism- - electron transfer • Oxydation- • Reduction-

3. How do microbes obtain energy? • Autotrophs- self feeders, use CO2 to sysnthesis organic compounds - Photoautotrophs- use sunlight for energy - Chemoautotrophs- use inorganics such as sulfides and nitrites for energy • Heterotrophs- other feeders, use organic molecules, - Photoheterotrophs-obtain chemical energy from light - Chemoheterotrophs- obtain energy from ready made organic compounds

4. What Is Energy? • Capacity to do work • Forms of energy • Potential energy, • Kinetic energy • Chemical energy • What Can Cells Do With Energy? • Cells use energy for: • Chemical work • Mechanical work • Electrochemical work

5. One-Way Flow of Energy • The sun is life’s primary energy source • Producers trap energy from the sun and convert it into chemical bond energy • Allorganisms use the energy stored in the bonds of organic compounds to do work

6. Endergonic Reactions • Energy input required • Product has more energy than starting substances glucose, a high energy product + 6O2 ENERGY IN 6 6 low energy starting substances 6 6

7. Exergonic Reactions • Energy is released • Products have less energy than starting substance glucose, a high energy starting substance + 6O2 ENERGY OUT low energy products 6 6

8. The Role of ATP • Cells “earn” ATP in exergonic reactions • Cells “spend” ATP in endergonic reactions base three phosphate groups sugar

9. ATP/ADP Cycle • When adenosine triphosphate (ATP) gives up a phosphate group, adenosine diphosphate (ADP) forms • ATP can re-form when ADP binds to inorganic phosphate or to a phosphate group that was split from a different molecule • Regenerating ATP by this ATP/ADP cycle helps drive most metabolic reactions

10. Energy carriers Enzymes Cofactors Transport proteins Participants in Metabolic Reactions • Reactants • Intermediates • Products

11. Chemical Equilibrium • At equilibrium, the energy in the reactants equals that in the products • Product and reactant molecules usually differ in energy content • Therefore, at equilibrium, the amount of reactant almost never equals the amount of product

12. Chemical Equilibrium

13. Redox Reactions • Cells release energy efficiently by electron transfers, or oxidation-reduction reactions (“redox” reactions) • One molecule gives up electrons (is oxidized) and another gains them (is reduced) • Hydrogen atoms are commonly released at the same time, thus becoming H+

14. Electron Transfer Chains • Arrangement of enzymes, coenzymes, at cell membrane • As one molecule is oxidized, next is reduced • Function in aerobic respiration and photosynthesis

15. Uncontrolled vs. Controlled Energy Release H2 1/2 O2 Explosive release of energy as heat that cannot be harnessed for cellular work H2O

16. Metabolic Pathways • Defined as enzyme-mediated sequences of reactions in cells • Biosynthetic (anabolic) – ex: photosynthesis • Degradative (catabolic) – ex: aerobic respiration

17. Enzyme Structure and Function • Enzymes are catalytic molecules • They speed the rate at which reactions approach equilibrium

18. Four Features of Enzymes 1) Enzymes do not make anything happen that could not happen on its own. They just make it happen much faster. 2) Reactions do not alter or use up enzyme molecules.

19. Four Features of Enzymes 3) The same enzyme usually works for both the forward and reverse reactions. 4) Each type of enzyme recognizes and binds to only certain substrates.

20. Activation Energy • For a reaction to occur, an energy barrier must be surmounted • Enzymes make the energy barrier smaller activation energy without enzyme starting substance activation energy with enzyme energy released by the reaction products

21. How Catalase Works

22. Induced-Fit Model • Substrate molecules are brought together • Substrates are oriented in ways that favor reaction • Active sites may promote acid-base reactions • Active sites may shut out water

23. Factors Influencing Enzyme Activity Temperature pH Salt concentration Allosteric regulators Coenzymes and cofactors

24. Enzyme Helpers • Cofactors • Coenzymes • NAD+, NADP+, FAD • Accept electrons and hydrogen ions; transfer them within cell • Derived from vitamins • Metal ions • Ferrous iron in cytochromes

25. Allosteric Activation enzyme active site allosteric activator vacant allosteric binding site active site cannot bind substrate active site altered, can bind substrate

26. Allosteric Inhibition allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can’t bind substrate

27. Feedback Inhibition enzyme 2 enzyme 3 enzyme 4 enzyme 5 A cellular change, caused by a specific activity, shuts down the activity that brought it about enzyme 1 END PRODUCT (tryptophan) SUBSTRATE

28. Effect of Temperature • Small increase in temperature increases molecular collisions, reaction rates • High temperatures disrupt bonds and destroy the shape of active site

29. Effect of pH

30. Producing the Universal Currency of Life • All energy-releasing pathways • require characteristic starting materials • yield predictable products and by-products • produce ATP

31. Main Types of Energy-Releasing Pathways Anaerobic pathways • Evolved first • Don’t require oxygen • Start with glycolysis in cytoplasm • Completed in cytoplasm Aerobic pathways • Evolved later • Require oxygen • Start with glycolysis in cytoplasm • Completed in mitochondria

32. Energy-Releasing Pathways

33. Main Pathways Start with Glycolysis • Glycolysis occurs in cytoplasm • Reactions are catalyzed by enzymes Glucose 2 Pyruvate (six carbons) (three carbons)

34. The Role of Coenzymes • NAD+ and FAD accept electrons and hydrogen from intermediates during the first two stages • When reduced, they are NADH and FADH2 • In the third stage, these coenzymes deliver the electrons and hydrogen to the transfer chain

35. Anaerobic Pathways • Do not use oxygen • Produce less ATP than aerobic pathways • Two types of fermentation pathways • Alcoholic fermentation • Lactate fermentation

36. Fermentation Pathways • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis • Steps that follow glycolysis serve only to regenerate NAD+

37. Alcoholic Fermentation

38. Yeasts • Single-celled fungi • Carry out alcoholic fermentation • Saccharomyces cerevisiae • Baker’s yeast • Carbon dioxide makes bread dough rise • Saccharomyces ellipsoideus • Used to make beer and wine

39. Lactate Fermentation • Carried out by certain bacteria • Electron transfer chain is in bacterial plasma membrane • Final electron acceptor is compound from environment (such as nitrate), not oxygen • ATP yield is low

40. Lactate Fermentation

41. Carbohydrate Breakdown and Storage • Glucose is absorbed into blood • Pancreas releases insulin • Insulin stimulates glucose uptake by cells • Cells convert glucose to glucose-6-phosphate • This traps glucose in cytoplasm where it can be used for glycolysis

42. Glycolysis Occurs in Two Stages Energy-requiring steps • ATP energy activates glucose and its six-carbon derivatives • Energy-releasing steps • The products of the first part are split into three-carbon pyruvate molecules • ATP and NADH form

43. Energy-Requiring Steps

44. Energy-Releasing Steps

45. Net Energy Yield from Glycolysis Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH

46. Overview of Aerobic Respiration • Overview of Aerobic Respiration C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxide

47. Overview of Aerobic Respiration

48. Second-Stage Reactions • Occur in the mitochondria • Pyruvate is broken down to carbon dioxide • More ATP is formed • More coenzymes are reduced

49. Two Parts of Second Stage • Preparatory reactions • Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide • NAD+ is reduced • Krebs cycle • The acetyl units are oxidized to carbon dioxide • NAD+ and FAD are reduced

50. Preparatory Reactions pyruvate + coenzyme A + NAD+ acetyl-CoA + NADH + CO2 • One of the carbons from pyruvate is released in CO2 • Two carbons are attached to coenzyme A and continue on to the Krebs cycle