Metabolic Pathways PDF

Sooty Grouse hen Near Lake Tahoe, CA Metabolic Pathways Ch. 8 Overview of Carbohydrate Catabolism Carbohydrates serve as primary energy source for most microbes Involves the oxidation of glucose Oxidation – loss of e- (and H+ sometimes) e- collected using elec...

Sooty Grouse hen Near Lake Tahoe, CA Metabolic Pathways Ch. 8 Overview of Carbohydrate Catabolism Carbohydrates serve as primary energy source for most microbes Involves the oxidation of glucose Oxidation – loss of e- (and H+ sometimes) e- collected using electron carriers (NAD+ or FAD) e- contain energy used to generate ATP 3 basic pathways involved Energy-generating pathways in microbes 1. Aerobic respiration Respiration is an ATP-generating process in which glucose is oxidized, e- are captured, and the final e- acceptor is an inorganic molecule. Final e- acceptor in aerobic respiration is O2. 2. Anaerobic respiration Final e- acceptor is inorganic molec. other than O2. ex. NO3-, SO42-, CO32- 3. Fermentation Final e- acceptor is an organic molecule (ex. pyruvate).  Compare and contrast the 3 processes: 1. Purpose? 2. Final e- acceptor? 3. Amount of ATP generated? 4. Use of Krebs and ETC? Aerobic Respiration Overall formula C6H12O6 🡪 6 CO2 + 6 H2O + energy (ATP) Energy yield Prokaryotes – 38 ATP/glucose Eukaryotes – 36 ATP/glucose Location Prokaryotes – cytoplasm and across the plasma membrane Eukaryotes – cytoplasm, mitochondrial matrix, and across the mitochondrial membrane 3 steps of aerobic respiration 1. Glycolysis Glucose is partially oxidized, split into 2 3C molecules (pyruvate), generates 2 ATP/glucose and 2 reduced e- carriers. 2. Kreb’s cycle Pyruvate is completely oxidized to CO2, lots of reduced e- carriers are generated, 2 GTP (similar to ATP) generated/glucose. 3. Electron transport chain e- carriers from glycolysis, Kreb’s are used to generate ATP via chemiosmosis, final e- acceptor is O2. Overview of Glucose Catabolism e- e- What we need to look for: 1. Did we lose a carbon (CO2) in the reaction? (decarboxylation) 2. Did we generate any ATP in this reaction (substrate-level phosphorylation)? 3. Is this a redox reaction? If so, what is being oxidized in the reaction, what is being reduced? Glycolysis Location: cytoplasm Does not require O2 10 steps Preparatory – glucose is phosphorylated (- 2ATP) and split into 2 3C units Energy-yielding - the 3C units are oxidized (2 e- carriers), 4 ATP generated Net yield 2ATP (substrate lvl. phosphorylation 2 NADH+ (reduced e- carriers) 2 pyruvates (3C units) A close-up of one reaction Are we losing a carbon? This is a redox reaction! Are we generating any ATP via What is being oxidized in this substrate-level phosphorylation? reaction? What is being reduced? What happens to pyruvate? Kreb’s cycle Fig. 4.21 Location: Prokaryotes – cytoplasm Eukaryotes – mitochondrial matrix  Kreb’s Cycle Part of respiration (requires O2 if aerobic) Entry Step: Complete oxidation of glucose to 6 CO2 Net yield: 2 GTP/glucose (substrate lvl. phosphorylation) decarboxylation 6 NADH/glucose redox 2 FADH2/glucose  Krebs Cycle 4C OAA regenerated 2C + 4C = 6C citric acid redox decarboxylation and redox redox decarboxylation and redox substrate lvl. phosphorylation (of GTP) Electron Transport Chain (Where Oxidative Phosphorylation Happens) Location Prokaryotes: across plasma membrane Eukaryotes: across inner mitochondrial membrane Reduced e- carriers (NADH, FADH2) pass e- to membrane complexes Reduction of membrane complexes allows a H+ to be pumped across membrane Creates H+ gradient Final e- acceptor is O2 (to make H2O) ETC (euk) ETC (prok) Summary of Aerobic Respiration (per glucose) Glycolysis 2 ATP (substrate lvl.) 2 NADH (e- transport) Krebs cycle 8 NADH (e- transport) 2 FADH2 (e- transport) 2 GTP (substrate lvl.) 3 ATP/NADH Electron transport 2 ATP/FADH2 38 ATP/glucose for prokaryotes Grand totals 36 ATP/glucose for eukaryotes Why the difference in ATP production between prokaryotes and eukaryotes? (or why prokaryotes rule the earth!!!) In eukaryotes, NADH from glycolysis is produced in the cytoplasm, but is used in the mitochondrion for e- transport. Those 2 NADH are actively transported across the mitochondrial membrane for the cost of 1 ATP each. So eukaryotes have a -2 ATP cost because they sequester the e- transport chain in their mitochondria – prokaryotes do not.  How do other foods fit in? Fatty Acid Catabolism: Amino Acid Catabolism: β-oxidation deamination Amino Acid Anabolism: Fatty Acid Anabolism: various glycolysis and Acetyl-CoA Krebs intermediates Fermentation An alternative to aerobic respiration in some cells (not all). Does not use O2. Does not use the Krebs cycle or the e- transport chain. Final e- acceptor is an organic molecule (pyruvate or a derivative) Energy yield is lower – only 2 ATP/glucose Is an incomplete oxidation of glucose. Recycles NAD+ to keep glycolysis going  Many different fermentation pathways (especially in prok)  2 common fermentation reactions Lactic acid fermentation Alcohol (ethanol) fermentation When no O2 is available, where do we put the e- captured by NAD+ in glycolysis? Pyruvate!!! Anaerobic Respiration Inorganic final e- acceptor – not O2 Uses modified Kreb’s cycle and e- transport chains Energy yield per glucose is generally less than aerobic respiration but greater than fermentation (>2 ATP but < 38 ATP/glucose) Some important anaerobic reactions Members of the genera Bacillus, Pseudomonas NO 🡪 3 - NO2- (N cycle in soils) nitrates nitrites Desulfovibrio SO 🡪 4 2- H2S (wetlands, swamps) sulfates swamp gas Sewage treatment CO 🡪 3 2- CH4 carbonates methane Yellow-headed Blackbird Near Portola, CA