Introduction
Bacteria show an incredible diversity with regards to their use of different energy
sources.
An overview of a hypothetical bacterial cell:
Substrates
Energy conservation (ATP and transmembrane potential)
Biosynthesis
Transport
Movement
Cell division
Energy and Carbon Metabolism: An overview
Energy
Chemotrophs
Chemo-lithotrophs
Chemo-organotrophs
Carbon
metabolism
Heterotroph
Autotroph
(CO2)
Phototrophs
Basic principles
The common denominators in energy metabolism are
ATP and transmembrane potentials
Mechanisms for the generation of ATP
Substrate level phosphorylation
Respiration
Photophosphorylation
Adenosine-5'-triphosphate (ATP)
Figure 8.3
Oxidation / Reduction (Redox) reactions
Redox reactions:
Oxidation is the loss of electrons and reduction is the gain of
electrons. Electrons cannot exist in solution and the loss of electrons
must be coupled to the gain of electrons.
Reduction potential:
This is a quantitqtive measure of the tendency for a substance to give
up electrons in biological systems. It is measured in volts and
generally at pH = 7.0.
Half reactions
Half reaction are a convenient way of showing the reduced and
oxidized form of a compound. Two half reactions are coupled to give
a redox reaction.
Half reactions Table
8.1
The number of electrons
transferred (n), and the
electrode potential under
standard conditions (E0')
compared to the hydrogen half
cell.
Relationship between free energy and
reduction potential
Go = -nF  Eh
Go = Change in Free energy
n = number of electrons in reaction
F = Faradays constant
 Eh = E’ (oxidized) - E’ (reduced)
ATP hydrolysis releases –31.8 kJ
/ mole so we need at least this
amount of energy to make a
phosphodiesterase bond in ATP.
Nicotinamide adenine dinucleotide (NAD)
Respiration and fermentation
Fermentation: Energy generation by anaerobic energy-yielding reactions
characterized by substate level phosphorylation and the absence of
cytochrome-mediated electron transfer.
Respiration: Energy generation in which molecular oxygen or some other
oxidant is the terminal electron acceptor. Among the latter are nitrate,
sulfate, carbon dioxide and fumarate.
Energy and Carbon Metabolism: Fermentative
organisms
Energy
Chemotrophs
Chemo-lithotrophs
Chemo-organotrophs
Carbon
metabolism
Heterotroph
Autotroph
(CO2)
Phototrophs
Glycolysis
Substrate level phosphorylation
There are three basic reactions. 1 and 2 are found in most aerobic and
anaerobic bacteria which grow on sugars. 3 is found mainly in anaerobic
fermenting bacteria.
1. 1,3 bis-phosphoglycerate + ADP
3 phosphoglycerate + ATP
2. phosphoenol pyruvate + ADP
pyruvate + ATP’
3. acetyl phosphate + AMP
acetate + ATP
An example of substrate level phosphorylation
Acetyl-coenzyme A
(acetyl-CoA)
The thioester bond between
the β-mercaptoethylamine
moiety of CoA and the
acetyl groups (~) is an
energy-rich bond.
Stickland reaction
Respiration and fermentation
Fermentation: Energy generation by anaerobic energy-yielding reactions
characterized by substate level phosphorylation and the absence of
cytochrome-mediated electron transfer.
Respiration: Energy generation in which molecular oxygen or some other
oxidant is the terminal electron acceptor. Among the latter are nitrate,
sulfate, carbon dioxide and fumarate.
Energy and Carbon Metabolism: respiration
Energy
Chemotrophs
Chemo-lithotrophs
Chemo-organotrophs
Carbon
metabolism
Heterotroph
Autotroph
(CO2)
Phototrophs
Energy transducing membranes
Components of the electron transport chains
Flavo proteins: carry two electrons (e-) and two protons H+)
Iron sulphide proteins: carry one electron (e-)
Quinones: carry two electrons (e-) and two protons H+)
Cytochromes: carry one electron (e-)
Flavin nucleotides, components of
flavoproteins
Iron-sulfur groups, components of nonheme
iron proteins
Coenzyme Q (ubiquinone)
The heme portion of a cytochrome molecule
The electron transport chain operating during
aerobic growth in Paracoccus denitrificans.
The electron transport chain of Thiobacillus
ferrooxidans, which uses Fe2+ as an energy
source
The structure of ATP
synthase, showing
the F0 and F1
subunits.
Diversity
In this lecture I have covered basic themes but at the begining of the
lecture I said something about metabolic diversity.
This diversity is generated from variation in the electron donor (organic
(thousands to choose from) or inorganic ( a few to chose from)) terminal
electron acceptor organic (fermentation) or inorganic (respiration).
Use of light energy in the phototrophs.