Microbial Metabolism Microbiology 274 March 22, 2007 Free energy of reactions Temperature ∆G = ∆H - T∆S Free Energy: How much energy during a reaction is available to work Entropy: Enthalpy: How much heat is lost or gained during the reaction How much randomness is lost or gained during the reaction Page 152 in your text Free energy of reactions  Exergonic reaction: ∆G°’ is negative A+B  C+D Endergonic reaction: ∆G°’ is positive A+B C+D Figure 8.5 Metabolism  Organisms need to synthesize many complex organic molecules  Synthesis from monomers to polymers these reactions are endergonic and require a source of energy ATP ATP is used as a source of energy to change endergonic reactions to exergonic reactions Energy Coupling A+B C+D ATP A+B ADP + Pi C +enzyme D Figure 8.6 Enzymes as catalysts for reactions  Enzymes are proteins  Highly specific for the reaction that they catalyze  Reduce the energy of activation (E ) of a reaction a C6H12O6 + O2 CO2 + H2O Ea ∆G°’ Figure 8.14 is similar Back to ATP… ATP is constantly depleted by cells ADP + P = ATP i ∆G = 7.3 kcal/mole In order to make more ATP, cells need to input energy… Oxidation-Reduction Reactions  Loss of Electrons = Oxidation (LEO)  Gain of Electrons = Reduction (GER)  Electron Donors and Electron Acceptors Acceptor + ne- Donor Page 153 in your text Standard Reduction Potential  Measure of the tendency of a donor to lose electrons (E’ ) 2H+ + 2eNAD+ + 2H+ + 2e- H2 E’0 = -420 mV NADH + H2 E’0 = -320 mV /2O2 + 2H+ + 2emV H 2O E’0 = +820 E coli Electron Transport System H+ cytochrome o H+ H+ periplasmic space cytochrome d Q FeS FAD cytoplasm 2H + /2O2 + 2H+ + 1/2O2 H2O NADH + H+ NAD+ H2O Figure 9.15 E coli Electron Transport System  Cytochrome d has a high affinity for oxygen, but does not pump hydrogen across the membrane  Active is low pathway when environmental oxygen  Cytochrome o has a low affinity for oxygen and acts as a hydrogen pump  Active is high pathway when environmental oxygen Proton Motive Force • Accumulation of protons on one side of a biological membrane creates an electrochemical imbalance = potential energy H H+ H+ H+ H+ H+ H+ H+ H+ + + H+ H + H + + H H H + + H+ H+ + H+ H H+ H+ H H H+ + + + H H H + H H+ H+ H+ + + + + H + + + H H + + + + H H H H H H H H + H+ H+ H+ H + H+ H+ H+ H + H+ H+ H+ Proton motive force drives ATP Synthase H H+ H+ H+ H+ H+ H+ H+ H+ H + H + H+ H+ H+ + H + + H+ H+ + H+ H H+ H+ H H H+ + + + H H H + H H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ + H+ H + H ATP Synthase + H+ H H+ H+ H+ + H+ ATP ADP H+ H+ = Oxidative Phosphorylation ATP Yield from the Aerobic Oxidation of Glucose by Eukaryotic Cells   Glycolytic Pathway  Substrate-level phosphorylation (ATP) ATP  Oxidative phosphorylation (NADH x 2) 4-6 ATP Pyruvate to Acetyl CoA   ATP Oxidative phosphorylation (NADH x 2) Tricarboxylic Acid Cycle ATP  Substrate-level phosphorylation (ATP) 18 ATP  Oxidative phosphorylation (NADH x 6) ATP  Oxidative phosphorylation (FADH2 x 2) Total Aerobic Yield 36-38 ATP Protein Catabolism  Bacteria can secrete proteases to digest proteins to amino acids  Amino acids are converted to pyruvate, acetyl CoA or a TCA cycle intermediate… Synthesis of NADH and FADH and subsequent oxidative phosphorylation Lipid Catabolism Fats lipases Glycerol Dihydroxyacetone phosphate Fatty acids β-oxidation cycle Acetyl CoA, NADH, FADH2 Glycolysis (continued) Glyceraldehyde 3- P Pi 1,3-Bisphosphoglycerate Dihydroxyacetone- P NAD+ NADH + H+ ADP 3-Phosphoclycerate 2-Phosphoglycerate dehydrogenase ATP phosphoglycerate kinase phosphoglycerate mutase Anaerobic Respiration  Use of electron acceptors other than oxygen  Examples:  Nitrate (NO3-)  Sulfate (S042-)  Carbon Dioxide (C02) Figure 8-7 Denitrification e.g Pseudomonas sp Nitrate (NO -) Nitrite (NO -) Ammonia (NH ) Nitrate (NO -) (N ) Nitrite (NO -) nitrous oxide (N 0) dinitrogen gas Terminal oxidase = Nitrate reductase synthesis of this enzyme is turned on when oxygen is absent, inhibited when oxygen present Take-Home Message  Organisms require ATP to grow  ATP is synthesized as a result of the catabolism of a variety of nutritional sources, through a variety of metabolic pathways  ATP synthesis is linked to the transfer of electrons (energy) from molecules of high redox potential to molecules of low redox potential  The presence of an efficient electron acceptor allows increased ATP synthesis Methanogens Obligate anaerobic archaeobacteria reduce CO methane CO + H + H = CH + H O 2 Methanogens often live in the same environment as H producing bacteria (fermentation) and will use it as it is produced ... during the reaction Page 15 2 in your text Free energy of reactions  Exergonic reaction: ∆G°’ is negative A+B  C+D Endergonic reaction: ∆G°’ is positive A+B C+D Figure 8.5 Metabolism  Organisms... that they catalyze  Reduce the energy of activation (E ) of a reaction a C6H12O6 + O2 CO2 + H2O Ea ∆G°’ Figure 8 .14 is similar Back to ATP… ATP is constantly depleted by cells ADP + P = ATP... Fructose 6-phosphate ATP Fructose 1, 6-bisphosphate phosphofructokinase ADP aldolase Glyceraldehyde 3- P Dihydroxyacetone- P Glycolysis (continued) Glyceraldehyde 3- P Pi 1, 3-Bisphosphoglycerate Dihydroxyacetone-