Download Aerobic respiration

Lecture 6, 2005
Fig. 6.24. Catabolism of other organic compounds
Physiology cont.
Table 6.8. Aerobic respiration in chemoautotrophs.
Review:
Respiration - e- donor can be organic or inorganic
Aerobic respiration - O2 is final e- acceptor.
Anaerobic respiration - Other final e- acceptor
(e.g. NO3 -).
Fermentation (today)
Phenolic respiration same as sugar (Fig. 6.8)..
See Figure 6.25. and
i.e.
Overheads….
in
oxidation of the substrate,
reduction of NAD+,
oxidation of NADH at the e- transport chain,
pumping of protons by the e- transport chain,
ATPase used to make ATP as protons flow back
Aerobic vs. anaerobic respiration in E. coli
The order of catabolic reactions in a sediment…..
Differences:
Note oxygenase step needed to break ring
Fermentation
Internally balanced oxidation-reduction reaction
Regeneration of NAD+
Different from respiration because no etransport chain.
Let’s start with fermentation of sugar (e.g. glucose)
Start with glycolysis (same as with resp. of glucose)……
First step: Fig. 3.30 then glycolysis….
Fate of pyruvate is varied depending on
the organism…
Fig. 6.23. Endproducts (primary metabolites)
of fermentation reactions in various
microbes…
Fig. 06.22Fig. 6.22
Regeneration of NAD+ without
an e- transport chain…….
Lactic Acid Fermentation
Alcoholic Fermentation - 2 step process
PYRUVATE
PYRUVATE
NADH
NAD+
LacticAcid
ACETALDEHYDE
+
CO2
NADH
Used to make yogurt, sauerkraut and pickles.
ETHANOL
NAD+
Used to make bread, wine, and beer.
Types of fermentations in a little more detail - See overheads….
Making ATP without an
e-
transport chain or ATPases…
1) Mixed acid fermentation - organisms excrete ethanol and a
mixture of acids including acetic, lactic, succinic, and formic
acids. Seen in Escherichia, Salmonella, Proteus, and
some others
Substrate-level phosphorylation
See figures……
2) Butanediol fermentation - Pyruvate converted to
acetoin, which is then reduced to 2,3-butanediol as
well as ethanol. Characteristic of Enterobacter,
Serratia, and some Bacillus Basis of some diagnostic tests,
including Voges-Proskauer.
3) Stickland reaction… found in many clostridia
that live in rich environments…. Use 2
amino acids - one as an e- donor and one as
an e- acceptor
Last examples of important fermentations:
Heterolactic fermentation:
Glucose ----> 1 ethanol + 1 lactate
That was all fermentation - the generation of
energy without terminal electron acceptors.
Why did fermentation yield so little ATP?
Homolactic fermentation:
Glucose ----> 2 lactates
1) The carbon compounds are only partially
oxidized.
See overhead for details of NAD+ regeneration
2) The reduction potentials between primary
electron donor and terminal electron acceptor
are small.
If O2 or another terminal electron acceptor is
used, the carbon can be oxidized completely to
CO2.
Anabolic reactions:
If O2 is used = aerobic respiration
Require energy input, used for making biomass
Fig. 6.29
Fig. 6.30. A. Amine incorporation to form glutamate.
B. transanimation reaction to form other amino acids
Fig. 6.31
Fig. 6.32
Many bacteria can biosynthesize all of their biomass
from simple molecules (e.g. nitrate, phosphate,
glucose etc)….. e.g. E. coli can grow in media
containing only glucose and six inorganic salts….
Non-fastidious microbes often need anaplerotic
reactions to replenish intermediates in biosynthetic
pathways……. These reactions are especially
important during the lag phase to “prime the pump”
Others are more “fastidious” and require the presence
of exogenous amino acids and other organic
compounds, e.g. many pathogens and symbionts are
fastidious….. e.g. Some Neisseria spp. can only be
grown in the lab in the presence of all 20 amino acids
and 7 vitamins…. (Please read page 91)
See overhead…… Anaplerotic reaction, an example
of starting the TCA cycle in an awakening
bacterium…
Pyruvate + ATP + CO2 ---> Oxaloacetate + ADP