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

Overview of bacterial aerobic respiration

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

An outline of the reactions of glycolysis

Preparatory stage

Energy-conserving stage

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

Irreversible oxidative reactions

Reversible non-oxidative reactions

The Pentose Phosphate Pathway

The most common route for the conversion of hexoses to

pyruvate

Generally found in Pseudomonas, Rhizobium, Azotobacter,

Agrobacterium and Enterococcus faecalis

The Entner-Doudoroff Pathway

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

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

The Krebs cycle

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

Glucose metabolism and the electron transport chain of bacteria

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)

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

An electron transport chain

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

Electron transport and the chemiosmotic generation of ATP

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