Microbial Metabolism: Catabolic and Anabolic Pathways Microbial Metabolism: The Chemical Crossroads of Life Microbiology: A Systems Approach Microbial Metabolism: Catabolic and Anabolic Pathways Chapter 8 (p. 211-231) Copyright © The McGraw-Hill Companies, Inc) Permission required for reproduction or display. Chapter 8, pages 198 to 231

Learning Objectives: Explain the overall function of metabolic pathway Describe the chemical reactions in glycolysis Explain the products of the Krebs cycle Describe the chemiosmotic model for ATP generation Compare and contrast aerobic and anaerobic respiration Describe the chemical reactions and list some products of fermentation. Describe how lipids and proteins undergo catabolism Define amphibolic pathways Contrast oxygenic and anoxygenic photosynthesis.

Metabolic Pathways

Carbohydrate Catabolism The breakdown of carbohydrates to release energy Glycolysis Krebs cycle Electron transport chain

Glycolysis Oxidation of glucose to pyruvic acid Produces ATP and NADH.

Preparatory Stage Two ATPs are used 1 Two ATPs are used Glucose is split to form two phosphorylated 3-carbon sugars 3 4 5

Energy-Conserving Stage Two 3-carbon sugars oxidized to two Pyruvic acid molecules Four ATP produced (substrate level phosphorylation) Two NADH produced 9

Microbial Metabolism: The Chemical Crossroads of Life Glycolysis Summary Microbiology: A Systems Approach One glucose is used Partial oxidation of the sugar, 2 pyruvates are end products Two NADH are reduced 2 ATP are consumed, 4 ATP total are made, net of 2 ATP produced Chapter 8, pages 198 to 231

Intermediate Step Pyruvic acid (from glycolysis) is oxidized and decarboxylated.

Krebs Cycle Complete oxidation of acetyl CoA to CO2 produces NADH and FADH2.

Microbial Metabolism: The Chemical Crossroads of Life Krebs Cycle Summary Microbiology: A Systems Approach Pyruvate 1 3 CO2 4 NADH 1 FADH2 1 ATP Pyruvate 2 3 CO2 4 NADH 1 FADH2 1 ATP Glucose has now been completely oxidized to carbon dioxide Electrons are temporarily on carrier molecules 2 ATP total made by substrate level phosphorylation Chapter 8, pages 198 to 231

The Electron Transport Chain A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain. Energy released can be used to produce ATP by chemiosmosis.

Electron Transport System NADH oxidized Electrons pass through membrane carriers Protons pumped out (work is done) Electrons accepted by an inorganic molecule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell wall H H H H H H H H H H H Cytochromes H H H Cytoplasm H H ATP synthase ADP Cell membrane with ETS H ATP H H H

Microbial Metabolism: The Chemical Crossroads of Life Aerobic Respiration Microbiology: A Systems Approach The electron acceptor is an oxygen This is a very good acceptor Yields water upon reduction Because so much energy is released, the cell can pump out about 10 protons Occurs in bacterial membrane and mitochondria of eukaryotes Chapter 8, pages 198 to 231

Anaerobic Respiration Microbial Metabolism: The Chemical Crossroads of Life Anaerobic Respiration Microbiology: A Systems Approach The electron acceptor is not oxygen Examples: nitrate, nitrite, and sulfate These are mediocre acceptors – not as good as oxygen Yields other inorganic molecules upon reduction Less favorable reactions pump out fewer protons Chapter 8, pages 198 to 231

Anaerobic Respiration Electron acceptor Products NO3– NO2–, N2 + H2O SO4– H2S + H2O CO32 – CH4 + H2O

Chemiosmosis Proton gradient is potential energy Allowing protons back into the cell can be coupled to work 3 protons entering drive the synthesis of 1 ATP Oxidative phosphorylation

Aerobic Respiration Yield Microbial Metabolism: The Chemical Crossroads of Life Aerobic Respiration Yield Microbiology: A Systems Approach 1 Glucose  6 CO2 2 ATP from glycolysis 2 NADH from glycolysis  6 ATP 2 ATP from Krebs cycle substrate level 8 NADH from Krebs cycle  24 ATP 2 FADH2 from Krebs cycle  4 ATP Total 36-38 ATP per glucose Chapter 8, pages 198 to 231

Microbial Metabolism: The Chemical Crossroads of Life Fermentation Microbiology: A Systems Approach Performed by anaerobic microorganisms Does not use Krebs cycle or ETC Primary purpose: Regenerate NAD for reuse The electron acceptor is an organic molecule Secondary purpose: Generate additional energy Energy yields are very small Chapter 8, pages 198 to 231

Microbial Metabolism: The Chemical Crossroads of Life Fermentation Microbiology: A Systems Approach NADH oxidized Organic molecule reduced Many possible end products Lactic acid Ethanol Vinegar Acetone AEROBIC RESPIRATION ANAEROBIC RESPIRATION FERMENTATION Glycolysis Glycolysis Glycolysis Glucose (6C) Glucose (6C) Glucose (6C) ATP ATP ATP NADH 2pyruvate (3C) NADH 2pyruvate NADH (3C) 2pyruvate (3C) CO2 CO2 CO2 Acety lCoA Acety lCoA FADH2 System: Homolactic bacteria; human muscle FADH2 System: Yeasts NADH Krebs CO2 NADH Krebs CO2 Lactic acid Acetaldehyde ATP ATP Ethanol Electrons Electrons Or other alcohols, acids, gases Electron transport Electron transport Glucose acceptor. O2 is final electron Non oxygen electron acceptors (examples: SO42–, NO3–, CO32– ) acetaldehyde, etc.). electron accept or (pyruvate, An organic molecule is final NAD ATP produced = 38 ATP produced = 2 to 36 ATP produced = 2 NADH Glycolysis H H C C C OH H O O Pyruvic acid CO2 H H C C H H O Acetaldehyde NADH NAD H H H H O H NAD O H C C OH H C C C O H H H H H Ethyl alcohol Lactic acid Chapter 8, pages 198 to 231

Fermentation

Fermentation Alcohol fermentation: Produces ethyl alcohol + CO2. Lactic acid fermentation: Produces lactic acid. Homolactic fermentation: Produces lactic acid only. Heterolactic fermentation: Produces lactic acid and other compounds.

Pathway Eukaryote Prokaryote Glycolysis Cytoplasm Intermediate step Krebs cycle Mitochondrial matrix ETC Mitochondrial inner membrane Plasma membrane

Lipid Catabolism Figure 5.20

Protein Catabolism Protein Amino acids Organic acid Krebs cycle Extracellular proteases Protein Amino acids Deamination, decarboxylation, dehydrogenation Organic acid Krebs cycle

Amphibolism GLUCOSE Enzymes Membranes Cell wall Storage Membranes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Enzymes Membranes Cell wall Storage Membranes Storage Chromosomes Cell structure Nucleic acids Starch Cellulose Lipids Fats Anabolism Proteins Macromolecule Nucleotides Amino acids Carbohydrates Fatty acids Building block Deamination Beta oxidation GLUCOSE Glycolysis Metabolic pathways Pyruvic acid Acetyl coenzyme A Catabolism Krebs cycle Simple products NH3 CO2 H2O

Photosynthesis Photo: Conversion of light energy into chemical energy (ATP) Light-dependent (light) reactions Synthesis: Fixing carbon into organic molecules Light-independent (dark) reaction, Calvin-Benson cycle

Oxygenic Photosynthesis Chlorophyll pigments Thylakoid membrane Capture light energy Electron transport Photophosphorylation Makes NADH and ATP Oxygen produced Algae, plants, and cyanobacteria

Anoxygenic Photosynthesis Microbial Metabolism: The Chemical Crossroads of Life Anoxygenic Photosynthesis Microbiology: A Systems Approach Purple bacteria (similar to photosystem II) Make ATP Can’t make NADH No oxygen produced Green bacteria (similar to photosystem I) Also make NADH Chapter 8, pages 198 to 231

Ribulose-1,5-bisphosphate Calvin Benson Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fix carbon dioxide Autotrophs Reverse of glycolysis 6 CO2  Glucose CO2 P P Splitting 6 Carbon intermediate 3-phosphoglyceric acid P P Ribulose-1,5-bisphosphate 5Carbon P ATP × 2 P ADP Calvin Cycle P P ADP ATP P P 1,3-bisphosphoglyceric acid Series of 7 Carbon and 5 Carbon intermediates P H P NADPH × 2 H P NADP P Glyceraldehyde-3 phosphate Glucose Fructose intermediates