Tricarboxcylic acid cycle Anaerobic, cell membrane or mitochondria Each pyruvate gives up its carbon as CO 2 –6 total Oxaloacetate is regenerated with every turn –Pick up molecule 2 ATP are produced –Substrate level phosphorylation

Net yield of product per glucose molecule: 6 CO2 2 ATP 8 NADH = 3 ATP 2 FADH2 = 2 ATP TCA cycle occurs twice per glucose

ELECTRON TRANPORT Aerobic or anaerobic Final electron acceptor: –aerobic respiration - oxygen –anaerobic respiration - CO 2, NO 3 -, SO 4 2 Inner mitochondrial membrane or plasma membrane Electrons move down chain and set up H+ gradient –drives chemiosmosis

Electron transport systems consist of separate protein complexes Oxidative Phosphorylation – series of redox reactions creating a stepwise release of energy

Proton Motive Force generated by chemical and electrical gradient Proton flow across membrane is exerogonic

Using the PMF, ATP synthesis is catalyzed by ATP synthase (ATPase), through a process called chemiosmosis

Complete Aerobic Catabolism of Glucose C 6 H 12 O 6 + 6O ADP + 36P → 6CO 2 + 6H 2 O + 36ATP –(eukaryote) C 6 H 12 O 6 + 6O ADP + 38P → 6CO 2 + 6H 2 O + 38ATP –(prokaryote) Typical net energy yield: 36 ATP for eukaryotes 38 ATP for prokaryotes By-products of aerobic respiration are H 2 O and CO 2

Substrate-Level Phosphorylation –2 ATP (net gain Glycolysis) –2 ATP (TCA cycle) –4 Total from substrate-level phosphorylation Oxidative Phosphorylation –6 ATP (NADH Glycolysis) –28 ATP (NADH/FADH 2 TCA cycle) –34 total from oxidative phosphorylation Total ATP gain ~ 36 to 38

Many compounds can serve as terminal electron acceptors Anaerobic Respiration

E.coli –Nitrate reduction –N e- + 2H + N H 2 0 Paracoccus, Bacillus and Pseudomonas –Denitrification –N0 3 - N0 2 - NO N 2 O N 2

Nitrate reduction and ammonification Denitrification in Paracoccus

Desulfovibrio –Reduce sulfate –acetate + SO H + 2CO 2 + H 2 S + 2H 2 O Archaea –Methanogens that reduce carbonate –HC H 2 + H + CH 4 + 3H 2 O

Common –Not associated with any one phylogenetic group –Except methanogenesis Involves: –membrane system –generation of ion gradient –formation of ATP via ATP synthase

Less efficient than aerobic respiration –Electron acceptors have less positive reduction potentials than oxygen – lower energy yield

Fermentation Used by organisms that can’t respire –lack of suitable inorganic electron acceptor or lack of electron transport chain Anaerobic; Occurs in the cytoplasm

–Partial oxidation of substrate NADH oxidized back to NAD+ Uses organic compound as terminal electron acceptor –Typically pyruvate or derivative NO oxidative phosphorylation so ATP yield is low

Lactic acid fermentation –pyruvate reduced to lactate –pyruvate accepts electrons and protons from NADH

Alcohol fermentation –pyruvate decarboxylated to form acetaldehyde –NADH transfers electrons and protons to acetaldehyde reducing it to ethanol

Catabolism of Other Organic Compounds Carbohydrates are the main energy source –glucose Microbes may also utilize lipids and proteins –Both must be broken down into their individual components –Each component is oxidized separately

Lipid Catabolism Lipases Fatty acids and glycerol –Fatty acid converted into acetyl CoA, enters TCA cycle –Glycerol converted into DHAP, enters glycolysis

Protein Catabolism Proteases Amino acids –can NOT be catabolized directly –transamination –decarboxylation –dehydrogenation