bacterial aerobic respiration
TRANSCRIPT
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