Life is based on redox • All energy generation in biological systems is due to redox (reduction-oxidation) reactions Aerobic Respiration: + - C6H12O6 + 6 H2O ==> 6 CO2 + 24 H +24 e oxidation electron donor (aka energy source) + - (O2+ 4H + 4e ==> 2H2O) x6 reduction electron acceptor --------------------------------------- C6H12O6 + 6 O2 ==> 6 CO2 + 6 H2O overall reaction (24 electrons) Types of bacterial metabolisms • While eukaryotes only reduce O2 and oxidize organic compounds, prokaryotes can use a variety of electron donors and acceptors, organic and inorganic. - • Aerobic respiration: e acceptor is O2 - • Anaerobic respiration: e acceptor is not O2 • Fermentation: e- donor and acceptor are organic molecules • Chemolithotrophy: e- donor and acceptor are inorganic molecules • Phototrophy: e- donor is light and e- acceptor is either organic or inorganic all microorganisms energy source? chemical light chemotroph phototroph carbon source? carbon source? organic organic CO CO compound 2 compound 2 chemoheterotroph chemoautotroph photoheterotroph photoautotroph e- acceptor? Nitrifying and sulfur- use H O to reduce CO ? oxidizing bacteria 2 2 green non-sulfur and O Other than O 2 2 purple non-sulfur bacteria anoxygenic oxygenic photosynthesis: photosynthesis: green sulfur and most bacteria Organic Inorganic cyanobacteria compound compound purple sulfur bacteria fermentative organism anaerobic respiration: nitrate, sulfate, Fe(III) Aerobic or anaerobic respiration Chemolithotrophy Important molecules Redox Electron Carrier: for example the NAD/NADH couple Energy storage compounds: ATP Coenzyme A NAD as a Redox Electron Carrier • freely diffusible carrier • nicotinamide-adenine dinucleotide NAD+ • transferring electrons from one place to another in the cell • carry 2 e- and 2 protons (H+) • NAD+/NADH -0.32 V - NADH is a good e- donor •NAD+ + 2 e- +2 H+ ==> NADH + H+ 2 [H] Coenzyme A • Conserve energy released in energy-producing reactions • Energy stored on thioester bond • Can store enough energy to drive the synthesis of ATP Acetyl-S-CoA + H2O +ADP+Pi ==> acetate + HS-CoA + ATP Metabolism fermentation lactate Substrate-level glucose glycolysis pyruvate phosphorylation butyrate ATP acetate Substrate-level NADH phosphorylation Acetyl-coA TCA Substrate-level ATP GTP ATP cycle phosphorylation NADH/ FADH2 Oxidative e- acceptor: phosphorylation - O2, NO3 or 2- SO4 Proton motive force ATPase ATP CAC= citric acid cycle Glycolysis Citric acid cycle • NADH and FADH coming from glycolysis will bring electrons NADH ==> NAD+ + e- + - FADH2 ==> FAD + e • These electrons are transported down the chain until they oxidize O2 • At each step, protons are translocated to outside the membrane • Thus, a proton gradient is established between inside and outside the cell • This proton gradient is termed the Oxidative Phosphorylation proton motive force (PMF) anaerobic respiration ATP generation with PMF • The proton motive force is used by ATP synthase to produce ATP. • Process called chemiosmosis Substrate level phosphorylation Other metabolisms Anaerobic food chain • In contrast to aerobic organisms, no single anaerobe is able to take glucose to CO2 • Need an anaerobic food chain that takes each compound part of the way. • Various organisms participate in the degradation of a polymeric sugar such as cellulose cellulose CH4 concentration acetate H2 fatty acids time Methanogenic environments 1 Fermentative bacteria Carbohydrates, nucleic acids 2 Syntrophic bacteria Proteins, lipids 3 Homoacetogenic bacteria 1 4 Methanogenesis Lactate Propionate Alcohols, … 2 3 H2, CO2 Acetate 4 CH4, CO2 Types of metabolisms • Fermentative bacteria: Diversity of fermentation types- use sugars, amino acids, nucleic acids- produce any combination of acids, alcohol, CO2, H2, NH3 • Syntrophic: Organisms that produces H2 and needs other organisms in co- culture to remove the H2 produced • Homoacetogenic: + - - 4 H2+ H + 2 HCO3 ==> CH3COO + 4 H2O acetate • Methanogenic (archea) 4 H2+ CO2 ==> CH4 + 2 H2O methane Sulfidogenic environments 1 Fermentative bacteria Carbohydrates 2 Syntrophic bacteria 3 Sulfate-reducing bacteria 1 Lactate Propionate 2 Alcohols, … 2 H2, CO2 Acetate 3 2- SO4 H2S and CO2 and/or acetate Important molecules pyruvate OH O OH C C O C C C O OH acetate C C C O OH C C lactate OH ethanol OH OH OH OH O C C C C O O C C C C O fumarate succinate OH OH OH O C C C C O C O OH malate formate.