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CHAPTER 5. MICROBIAL METABOLISM. Energy Chemical work Transport work Mechanical work Laws of thermodynamics 1 st 2 nd – entropy. Two fundamental tasks required for growth and reproduction Catabolism Anabolism. Metabolism Amazing diversity but also unity - PowerPoint PPT Presentation
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• Energy – Chemical work– Transport work– Mechanical work
• Laws of thermodynamics– 1st
– 2nd – entropy
• 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
Energy of Activation (EA)
• Catalysts (influence reaction rate):– Temperature
– Substrate Concentration
– Enzymes – biological catalysts
• 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
Factors influencing enzyme activity
• Denaturing stresses – Heat, pH, UV radiation, chemicals
• Substrate concentration• Competitive inhibition• Non-competitive (allosteric) inhibition
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
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
• 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
– 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 6-
phosphate, 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
• 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