Bacterial aerobic respiration

2.  Oxygen serves as the terminal electron acceptor for the
electron-transport chain in aerobic respiration
 The aerobic respiration in bacteria typically occurs in three
principal stages
 Glycolysis
 Krebs cycle
 Electron transport chain

3. Overview of bacterial aerobic respiration

4.  First stage in carbohydrate catabolism
 Oxidation of glucose to pyruvic acid
 Located in the cytoplasmic matrix of prokaryotes and eukaryotes
 Also called the Embden-Meyerhof pathway
 Does not require oxygen; it can occur whether oxygen is present
or not
 Two molecules of ATP are produced
 Consists of two basic stages; preparatory stage and energy-
conserving stage

5. An outline of the reactions of glycolysis
Preparatory stage
Energy-conserving stage

6. The Pentose Phosphate Pathway
 Also called the hexose monophosphate pathway
 Occurs in the cytosol of the cell
 No ATP is directly consumed or produced in the cycle
 Operate either aerobically or anaerobically
 Bacteria that use the pentose phosphate pathway include
Bacillus subtilis, E. coli, Leuconostoc mesenteroides and
Enterococcus faecalis

7. Irreversible oxidative reactions
Reversible non-oxidative reactions
The Pentose Phosphate Pathway

8.  The most common route for the conversion of hexoses to
pyruvate
 Generally found in Pseudomonas, Rhizobium, Azotobacter,
Agrobacterium and Enterococcus faecalis

9. The Entner-Doudoroff Pathway

10.  Also called the tricarboxylic acid (TCA) cycle or citric acid cycle
 Large amount of energy stored in acetyl CoA is released step by step
Oxidative decarboxylation of pyruvate
 Pyruvate is converted to acetyl CoA and CO2
 It is not part of the Krebs cycle, but is a major source of acetyl CoA
 NAD+ is reduced to NADH
 Acetyl-CoA arises from the catabolism of many lipids, carbohydrates
and amino acids

11.  The complete cycle appears to be functional in many aerobic
bacteria, free-living protozoa, and most algae and fungi
 The facultative anaerobe E. coli does not use the full Krebs
cycle under anaerobic conditions or when the glucose
concentration is high but does at other times
 One of Krebs cycle’s major functions is to provide carbon
skeletons for biosynthesis

12. The Krebs cycle

13.  Consists of a sequence of carrier molecules that are capable of
oxidation and reduction
 Electrons are passed through the chain
 Stepwise release of energy
 Which is used to drive the chemiosmotic generation of ATP
 The final oxidation is irreversible
 In eukaryotic cells - the electron transport chain is contained in
the inner membrane of mitochondria
 In prokaryotic cells - it is found in the plasma membrane

14. Glucose metabolism and the electron transport chain of bacteria

15.  There are three classes of carrier molecules in electron
transport chains
Flavoproteins
 Contain flavin, a coenzyme derived from riboflavin (vitamin B2)
 Capable of performing alternating oxidations and reductions
 One important flavin coenzyme is flavin mononucleotide
(FMN)

16. Cytochromes
 Proteins with an iron-containing group (heme)
 Capable of existing alternately as a reduced form (Fe2+) and an
oxidized form (Fe3+)
 The cytochromes involved in electron transport chains include
cytochrome b (cyt b), cytochrome c1 (cyt c1), cytochrome c
(cyt c), cytochrome a (cyt a), and cytochrome a3 (cyt a3)
Ubiquinones, or coenzyme Q
 small non-protein carriers

17. An electron transport chain

18.  Chemiosmosis - the mechanism of ATP synthesis using the
electron transport chain
 The movement of materials across membranes from areas of
high concentration to areas of low concentration; this
diffusion yields energy
 Energy released is used to synthesize ATP

19. Electron transport and the chemiosmotic generation of ATP

20. Source ATP yield (Method)
Glycolysis
Oxidation of glucose to pyruvate 2 ATP (substrate level phosphorylation)
Production of 2NADH 6 ATP (oxidative phosphorylation in electron
transport chain)
Preparatory step
Formation of acetyl CoA produces 2 NADH 6 ATP (oxidative phosphorylation in electron
transport chain)
Krebs cycle
Oxidation of succinyl CoA to succinate 2 GTP (equivalent of ATP; substrate level
phosphorylation)
Production of 6 NADH 18 ATP (oxidative phosphorylation in
electron transport chain
Production of 2FADH 4 ATP (oxidative phosphorylation in electron
transport chain)
Total: 38 ATP
ATP yield during prokaryotic aerobic respiration of one glucose
molecule