Download Metabolic Diversity

Life is based on redox
• All energy generation in biological systems is due to redox
(reduction-oxidation) reactions
Aerobic Respiration:
C6H12O6 + 6 H2O ==> 6 CO2 + 24 H+ +24 e(O2+ 4H+ + 4e- ==> 2H2O) x6
--------------------------------------C6H12O6 + 6 O2 ==> 6 CO2 + 6 H2O
oxidation electron donor
(aka energy source)
reduction electron acceptor
overall reaction (24 electrons)
Types of bacterial metabolisms
• While eukaryotes only reduce O2 and oxidize organic
compounds, prokaryotes can use a variety of electron
donors and acceptors, organic and inorganic.
• Aerobic respiration: e- acceptor is O2
• Anaerobic respiration: e- acceptor is not O2
• Fermentation: e- donor and acceptor are organic molecules
• Chemolithotrophy: e- donor and acceptor are inorganic
molecules
• Phototrophy: e- donor is light and e- acceptor is either
organic or inorganic
all microorganisms
energy source?
chemical
light
chemotroph
phototroph
carbon source?
organic
compound
carbon source?
CO2
chemoheterotroph
chemoautotroph
e- acceptor?
Nitrifying and sulfuroxidizing bacteria
O2
most bacteria
fermentative organism
photoheterotroph
CO2
photoautotroph
use H2O to reduce CO2?
green non-sulfur and
purple non-sulfur bacteria
Other than O2
Organic
compound
organic
compound
Inorganic
compound
anaerobic respiration:
nitrate, sulfate, Fe(III)
oxygenic
photosynthesis:
cyanobacteria
anoxygenic
photosynthesis:
green sulfur and
purple sulfur
bacteria
Aerobic or anaerobic respiration
Chemolithotrophy
Important molecules
Redox Electron Carrier: for example the NAD/NADH couple
Energy storage compounds: ATP
Coenzyme A
NAD as a Redox Electron Carrier
• freely diffusible carrier
• nicotinamide-adenine dinucleotide NAD+
• transferring electrons from one place to
another in the cell
• carry 2 e- and 2 protons (H+)
• NAD+/NADH -0.32 V - NADH is a good edonor
•NAD+ + 2 e- +2 H+ ==> NADH + H+
2 [H]
Coenzyme A
• Conserve energy released in energy-producing
reactions
• Energy stored on thioester bond
• Can store enough energy to drive the synthesis of ATP
Acetyl-S-CoA + H2O +ADP+Pi ==> acetate + HS-CoA + ATP
Metabolism
fermentation
lactate
glucose
glycolysis
Substrate-level
phosphorylation
ATP
pyruvate
Substrate-level
phosphorylation
butyrate
ATP
acetate
NADH
Acetyl-coA
TCA
cycle
GTP
Substrate-level
phosphorylation
NADH/ FADH2
Oxidative
phosphorylation
Proton motive force
ATPase
ATP
e- acceptor:
O2, NO3- or
SO42-
ATP
CAC= citric acid cycle
Glycolysis
Citric acid cycle
• NADH and FADH coming from
glycolysis will bring electrons
NADH ==> NAD+ + eFADH2 ==> FAD+ + e• These electrons are transported
down the chain until they oxidize
O2
• At each step, protons are
translocated to outside the
membrane
• Thus, a proton gradient is
established between inside and
outside the cell
Oxidative Phosphorylation
• This proton gradient is termed the
proton motive force (PMF)
anaerobic respiration
ATP generation with PMF
• The proton motive
force is used by ATP
synthase to produce
ATP.
• Process called
chemiosmosis
Substrate level phosphorylation
Other metabolisms
Anaerobic food chain
•
•
In contrast to aerobic organisms, no single anaerobe is able to take
glucose to CO2
Need an anaerobic food chain that takes each compound part of the
way.
Various organisms participate in the degradation of a polymeric sugar
such as cellulose
cellulose
concentration
•
CH4
acetate
H2
fatty acids
time
Methanogenic environments
1 Fermentative bacteria
Carbohydrates, nucleic acids
Proteins, lipids
2 Syntrophic bacteria
3 Homoacetogenic bacteria
1
4 Methanogenesis
Lactate
Propionate
Alcohols, …
2
H2, CO2
3
4
CH4, CO2
Acetate
Types of metabolisms
• Fermentative bacteria:
Diversity of fermentation types- use sugars, amino acids,
nucleic acids- produce any combination of acids, alcohol,
CO2, H2, NH3
• Syntrophic:
Organisms that produces H2 and needs other organisms in coculture to remove the H2 produced
• Homoacetogenic:
4 H2+ H+ + 2 HCO3- ==> CH3COO- + 4 H2O
acetate
• Methanogenic (archea)
4 H2+ CO2 ==> CH4 + 2 H2O
methane
Sulfidogenic environments
1 Fermentative bacteria
2 Syntrophic bacteria
Carbohydrates
3 Sulfate-reducing bacteria
1
2
H2, CO2
Lactate
Propionate
Alcohols, …
2
Acetate
3
SO42H2S and CO2 and/or acetate
Important molecules
pyruvate
OH
O OH
C C C
C C
O
O
OH
C C C
acetate
O
OH
C C
lactate
OH
ethanol
OH
OH
OH
O C C C C O
O C C C C O
fumarate
OH
O
C
succinate
OH
C C C O
OH
malate
OH
OH
C
O
formate