Life is based on redox All energy generation in biological systems is due to redox (reduction-oxidation) reactions Aerobic Respiration: C 6 H 12 O 6 + 6 H 2 O ==> 6 CO 2 + 24 H + +24 e - oxidation electron donor (aka energy source) (O 2 + 4H + + 4e - ==> 2H 2 O) x6 reduction electron acceptor --------------------------------------- C 6 H 12 O 6 + 6 O 2 ==> 6 CO 2 + 6 H 2 O overall reaction (24 electrons)
Types of bacterial metabolisms While eukaryotes only reduce O 2 and oxidize organic compounds, prokaryotes can use a variety of electron donors and acceptors, organic and inorganic. Aerobic respiration: e - acceptor is O 2 Anaerobic respiration: e - acceptor is not O 2 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 carbon source? phototroph carbon source? organic compound CO 2 organic compound CO 2 chemoheterotroph chemoautotroph photoheterotroph photoautotroph most bacteria e - acceptor? O 2 Other than O 2 Organic compound Nitrifying and sulfuroxidizing bacteria Inorganic compound green non-sulfur and purple non-sulfur bacteria use H 2 O to reduce CO 2? oxygenic photosynthesis: cyanobacteria anoxygenic photosynthesis: green sulfur and 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 + H 2 O +ADP+P i ==> acetate + HS-CoA + ATP
Metabolism lactate fermentation glucose glycolysis pyruvate Substrate-level phosphorylation butyrate Substrate-level phosphorylation NADH Acetyl-coA ATP acetate ATP TCA cycle GTP Substrate-level phosphorylation ATP NADH/ FADH 2 Oxidative phosphorylation Proton motive force e- acceptor: O 2, NO 3 - or SO 4 2- ATPase ATP
CAC= citric acid cycle
Glycolysis
Citric acid cycle
NADH and FADH coming from glycolysis will bring electrons NADH ==> NAD + + e - FADH 2 ==> FAD + + e - These electrons are transported down the chain until they oxidize O 2 At each step, protons are translocated to outside the membrane Thus, a proton gradient is established between inside and outside the cell Oxidative Phosphorylation This proton gradient is termed the 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 CO 2 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 concentration acetate CH 4 H 2 fatty acids time
Methanogenic environments Carbohydrates, nucleic acids Proteins, lipids 1 1 2 3 4 Fermentative bacteria Syntrophic bacteria Homoacetogenic bacteria Methanogenesis Lactate Propionate Alcohols, 2 H 2, CO 2 3 Acetate 4 CH 4, CO 2
Types of metabolisms Fermentative bacteria: Diversity of fermentation types- use sugars, amino acids, nucleic acids- produce any combination of acids, alcohol, CO 2, H 2, NH 3 Syntrophic: Organisms that produces H 2 and needs other organisms in coculture to remove the H 2 produced Homoacetogenic: 4 H 2 + H + + 2 HCO 3 - ==> CH 3 COO - + 4 H 2 O acetate Methanogenic (archea) 4 H 2 + CO 2 ==> CH 4 + 2 H 2 O methane
Sulfidogenic environments Carbohydrates 1 1 2 3 Fermentative bacteria Syntrophic bacteria Sulfate-reducing bacteria 2 Lactate Propionate Alcohols, 2 H 2, CO 2 3 SO 4 2- Acetate H 2 S and CO 2 and/or acetate
Important molecules pyruvate O OH C C C O OH C C C O OH C C O acetate C C OH ethanol O OH C OH malate OH C C C O O OH OH C C C C O fumarate OH lactate OH C O formate O OH OH C C C C O succinate