CHAPTER 5
MICROBIAL
METABOLISM
• Energy
– Chemical work
– Transport work
– Mechanical work
• Laws of thermodynamics
– 1st
– 2nd – entropy
• Two fundamental tasks required for growth
and reproduction
– Catabolism
– Anabolism
• Metabolism
– Amazing diversity but also unity
• Ordered, enzyme-mediated pathways
• ATP
• Redox
• Catabolic reactions
– hydrolytic, exergonic (-ΔG)
– Keq>1, spontaneous
– Cellular respiration
• Provides precursor molecules and energy for anabolic
reactions
• Anabolic reactions
– dehydration synthesis, endergonic (+ΔG)
– Keq<1, not favorable
– protein synthesis
• Consumes energy and precursor molecules in the
biosynthesis of macromolecules
Amphibolic reactions
Energy of Activation (EA)
• Catalysts (influence reaction rate):
– Temperature
– Substrate Concentration
– Enzymes – biological catalysts
• Enzymes:
• All protein or holoenzymes
– Apoenzyme + Cofactor (coenzyme)
• Characteristics of enzymes
– do not make reactions happen that could not
happen on their own
– not permanently altered or used up
– substrate-specific
– Function is based on structure
• Six functional categories of enzymes:
Unconventional Enzymes
• Ribozymes
– Novel type of RNA
• Extremozymes
– Have molecular applications
Mechanism of Enzymatic Action
Induced Fit model
Factors influencing enzyme activity
• Denaturing stresses
– Heat, pH, UV radiation, chemicals
• Substrate concentration
• Competitive inhibition
• Non-competitive (allosteric) inhibition
Feedback Inhibition
•Negative allosteric effection
Reduction-Oxidation Reactions
• Redox reactions liberate energy
– always coupled
– oxidation (electron donor)
– reduction (electron acceptor)
• Standard reduction potential (E`O)
• Reducing power (potential energy)
Reduction of NAD – common electron carrier
•Electrons and protons are typically removed together
•The equivalent of a hydrogen atom
NAD and
FAD are
common
electron
carriers
E’0 of various biologically
important redox couples
Electrons moving toward
less negative acceptors
release free energy
Amount of energy released
correlates with magnitude
of difference in E’0
ATP Synthesis
•
Free energy used to phosphorylate ADP forms ATP
–metabolic money!
• Substrate level phosphorylation
– chemical energy
• Oxidative phosphorylation
– energy from proton motive force
• Photophosphorylation
– radiant energy
Heterotrophic Metabolism
• Oxidize energy (electron) rich organic
molecules
• Typically utilize carbohydrates
– Glucose (C6H12O6) is #1 source
• Three possible pathways based on final
electron receptor
–Aerobic respiration – exogenous (oxygen)
–Anaerobic respiration – exogenous
–Fermentation – endogenous organic
pathways are
amphibolic and
provide
• Energy
• Reducing power
• Precursor metabolites
– Respiration uses reducing power to generate ATP
• NADH and FADH2 provide electrons to power proton
motive force
• Terminal electron acceptor varies
– Oxygen in aerobic respiration
– Anaerobic respiration uses alternate inorganic
molecule
GLYCOLYSIS
• Embden-Meyerhof Pathway
• Common pathway
• Glucose (6C) partially broken down into 2
molecules of pyruvate (3C)
– Anerobic; cytoplasm
• 2 NADH; 4 ATP
• 2 ATP consumed; so net gain of 2 ATP
– Substrate level phosphorylation
• Pentose phosphate pathway
– Produces many intermediate materials for
other pathways
• glyceraldehyde 3-phosphate, fructose 6phosphate, ribulose 5-phosphate
• If only 5 carbon sugars are available it can
biosynthesize 6 carbon sugars
– Major contributor to biosynthesis
• reducing power in NADPH
• vital precursor metabolites for anabolic pathways
• intermediates may be used to generate ATP
Pentose phosphate pathway
• Entner-Doudoroff pathway
– Alternate pathway to glycolysis
– typically not seen in G+ bacteria
– major contributor to biosynthesis
• reducing power as NADH and NADPH
• vital precursor metabolites for anabolic pathways
Entner-Doudoroff pathway