1. PowerPoint ® Lecture Presentations prepared by Mindy Miller-Kittrell, North Carolina State University C H A P T E R © 2014 Pearson Education, Inc. Microbial Metabolism 5

2. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism Metabolism Collection of controlled biochemical reactions that take place within a microbe Ultimate function of metabolism is to reproduce the organism

3. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism Metabolic Processes Guided by Eight Elementary Statements Every cell acquires nutrients Metabolism requires energy from light or catabolism of nutrients Energy is stored in adenosine triphosphate (ATP) Cells catabolize nutrients to form precursor metabolites Precursor metabolites, energy from ATP, and enzymes are used in anabolic reactions Enzymes plus ATP form macromolecules Cells grow by assembling macromolecules Cells reproduce once they have doubled in size

4. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism Catabolism and Anabolism Two major classes of metabolic reactions Catabolic pathways Break larger molecules into smaller products Exergonic (release energy) Anabolic pathways Synthesize large molecules from the smaller products of catabolism Endergonic (require more energy than they release)

5. © 2014 Pearson Education, Inc. Figure 5.1 Metabolism is composed of catabolic and anabolic reactions.

6. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism Oxidation and Reduction Reactions Transfer of electrons from an electron donor to an electron acceptor Reactions always occur simultaneously Cells use electron carriers to carry electrons (often in H atoms) Three important electron carriers Nicotinamide adenine dinucleotide (NAD + ) Nicotinamide adenine dinucleotide phosphate (NADP + ) Flavin adenine dinucleotide (FAD)

7. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism ATP Production and Energy Storage Organisms release energy from nutrients Can be concentrated and stored in high-energy phosphate bonds (ATP) Phosphorylation – inorganic phosphate is added to substrate Cells phosphorylate ADP to ATP in three ways Substrate-level phosphorylation Oxidative phosphorylation Photophosphorylation Anabolic pathways use some energy of ATP by breaking a phosphate bond

8. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism The Roles of Enzymes in Metabolism Enzymes are organic catalysts Increase likelihood of a reaction

9. © 2014 Pearson Education, Inc. Enzymes: Overview PLAY Enzymes: Overview

10. © 2014 Pearson Education, Inc. Basic Chemical Reactions Underlying Metabolism The Roles of Enzymes in Metabolism Naming and classifying enzymes Six categories of enzymes based on mode of action Hydrolases Isomerases Ligases or polymerases Lyases Oxidoreductases Transferases

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12. Basic Chemical Reactions Underlying Metabolism The Roles of Enzymes in Metabolism The makeup of enzymes Many protein enzymes are complete in themselves Apoenzymes are inactive if not bound to nonprotein cofactors (inorganic ions or coenzymes) Binding of apoenzyme and its cofactor(s) yields holoenzyme Some are RNA molecules called ribozymes

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14. Basic Chemical Reactions Underlying Metabolism The Roles of Enzymes in Metabolism Enzyme activity Many factors influence the rate of enzymatic reactions Temperature pH Enzyme and substrate concentrations Presence of inhibitors Inhibitors Substances that block an enzyme's active site Do not denature enzymes Three types

15. © 2014 Pearson Education, Inc. Figure 5.8 Denaturation of protein enzymes.

16. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Many organisms oxidize carbohydrates as primary energy source for anabolic reactions Glucose most common carbohydrate used Glucose catabolized by two processes: Cellular respiration Fermentation

17. © 2014 Pearson Education, Inc. Glucose NADH ATP 2 Pyruvic acid FADH 2 NADH ATP Electrons ADP ATP ELECTRON TRANSPORT CHAIN KREBS CYCLE Acetyl-CoA Final electron acceptor Formation of fermentation end-products Pyruvic acid (or derivative) ATP NADH GLYCOLYSISGLYCOLYSIS e–e– FermentationRespiration Figure 5.12 Summary of glucose catabolism.

18. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Glycolysis Occurs in cytoplasm of most cells Involves splitting of a six-carbon glucose into two three- carbon sugar molecules Substrate-level phosphorylation – direct transfer of phosphate between two substrates Net gain of two ATP molecules, two molecules of NADH, and precursor metabolite pyruvic acid

19. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Glycolysis Divided into three stages involving 10 total steps Energy-investment stage Lysis stage Energy-conserving stage

20. © 2014 Pearson Education, Inc. Figure 5.13 Glycolysis.

21. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration Resultant pyruvic acid completely oxidized to produce ATP by series of redox reactions Three stages of cellular respiration 1. Synthesis of acetyl-CoA 2. Krebs cycle 3. Final series of redox reaction (electron transport chain)

22. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration Synthesis of acetyl-CoA Results in Two molecules of acetyl-CoA Two molecules of CO 2 Two molecules of NADH

23. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration The Krebs cycle Great amount of energy remains in bonds of acetyl-CoA Transfers much of this energy to coenzymes NAD + and FAD Occurs in cytosol of prokaryotes and in matrix of mitochondria in eukaryotes

24. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration The Krebs cycle Six types of reactions in Krebs cycle Anabolism of citric acid Isomerization Redox reactions Decarboxylations Substrate-level phosphorylation Hydration reaction

25. © 2014 Pearson Education, Inc. Figure 5.16 The Krebs cycle.

26. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration The Krebs cycle Results in Two molecules of ATP Two molecules of FADH 2 Six molecules of NADH Four molecules of CO 2

27. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration Electron transport Most significant production of ATP occurs from series of redox reactions known as an electron transport chain (ETC) Series of carrier molecules that pass electrons from one to another to final electron acceptor Energy from electrons used to pump protons (H + ) across the membrane, establishing a proton gradient Located in cristae of eukaryotes and in cytoplasmic membrane of prokaryotes

28. © 2014 Pearson Education, Inc. Carbohydrate Catabolism Cellular Respiration Chemiosmosis Use of electrochemical gradients to generate ATP Cells use energy released in redox reactions of ETC to create proton gradient Protons flow down electrochemical gradient through ATP synthases that phosphorylate ADP to ATP Called oxidative phosphorylation because proton gradient is created by oxidation of components of ETC Total of ~34 ATP molecules formed from one molecule of glucose

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30. Carbohydrate Catabolism Fermentation Sometimes cells cannot completely oxidize glucose by cellular respiration Cells require constant source of NAD + Cannot be obtained simply using glycolysis and Krebs cycle Fermentation pathways provide cells with alternate source of NAD + Partial oxidation of sugar (or other metabolites) to release energy using an organic molecule from within the cell as final electron acceptor

31. © 2014 Pearson Education, Inc. Figure 5.22 Representative fermentation products and the organisms that produce them.

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33. Other Catabolic Pathways Lipids and proteins contain energy in their chemical bonds Can be converted into precursor metabolites Serve as substrates in glycolysis and the Krebs cycle

34. © 2014 Pearson Education, Inc. Extracellular fluid Proteases Polypeptide Amino acids Cytoplasmic membrane Cytoplasm Deamination To Krebs cycle Figure 5.24 Protein catabolism.

35. © 2014 Pearson Education, Inc. Photosynthesis Many organisms synthesize their own organic molecules from inorganic carbon dioxide Most of these organisms capture light energy and use it to synthesize carbohydrates from CO 2 and H 2 O by a process called photosynthesis

36. © 2014 Pearson Education, Inc. Photosynthesis Chemicals and Structures Chlorophylls Important to organisms that capture light energy with pigment molecules Composed of hydrocarbon tail attached to light- absorbing active site centered on magnesium ion Active sites structurally similar to cytochrome molecules in ETC Structural differences cause absorption at different wavelengths

37. © 2014 Pearson Education, Inc. Photosynthesis Chemicals and Structures Photosystems Arrangement of molecules of chlorophyll and other pigments to form light-harvesting matrices Embedded in cellular membranes called thylakoids In prokaryotes – invagination of cytoplasmic membrane In eukaryotes – formed from inner membrane of chloroplasts Arranged in stacks called grana Stroma is space between outer membrane of grana and thylakoid membrane

38. © 2014 Pearson Education, Inc. Photosynthesis Chemicals and Structures Two types of photosystems Photosystem I (PS I) Photosystem II (PS II) Photosystems absorb light energy and use redox reactions to store energy in the form of ATP and NADPH Light-dependent reactions depend on light energy Light-independent reactions synthesize glucose from carbon dioxide and water

39. © 2014 Pearson Education, Inc. Photosynthesis Light-Dependent Reactions As electrons move down the chain, their energy is used to pump protons across the membrane Photophosphorylation uses proton motive force to generate ATP Photophosphorylation can be cyclic or noncyclic

40. © 2014 Pearson Education, Inc. Photosynthesis Light-Independent Reactions Do not require light directly Use ATP and NADPH generated by light-dependent reactions Key reaction is carbon fixation by Calvin-Benson cycle Three steps Fixation of CO 2 Reduction Regeneration of RuBP

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42. Figure 5.29 The role of gluconeogenesis in the biosynthesis of complex carbohydrates.

43. © 2014 Pearson Education, Inc. Figure 5.30 Biosynthesis of fat, a lipid.

44. © 2014 Pearson Education, Inc. Integration and Regulation of Metabolic Function Cells synthesize or degrade channel and transport proteins Cells often synthesize enzymes only when substrate is available Cells catabolize the more energy-efficient choice if two energy sources are available Cells synthesize metabolites they need, cease synthesis if metabolite is available

45. © 2014 Pearson Education, Inc. Integration and Regulation of Metabolic Function Eukaryotic cells isolate enzymes of different metabolic pathways within membrane-bounded organelles Cells use allosteric sites on enzymes to control activity of enzymes Feedback inhibition slows/stops anabolic pathways when product is in abundance Cells regulate amphibolic pathways by requiring different coenzymes for each pathway

46. © 2014 Pearson Education, Inc. Integration and Regulation of Metabolic Function Two types of regulatory mechanisms Control of gene expression Cells control amount and timing of protein (enzyme) production Control of metabolic expression Cells control activity of proteins (enzymes) once produced