Microbial Microbial Metabolism Metabolism Energy Production Energy Production
Microbial MetabolismMicrobial MetabolismEnergy ProductionEnergy Production
Energy productionEnergy production Nutrient molecules have energy associated Nutrient molecules have energy associated
with the electrons that form bonds between with the electrons that form bonds between atomsatoms
Catabolic reactions oxidize nutrients by Catabolic reactions oxidize nutrients by removing electrons and concentrate their removing electrons and concentrate their energy into the bonds of ATPenergy into the bonds of ATP
ATP has “high energy” or unstable bonds ATP has “high energy” or unstable bonds which allows the energy to be released which allows the energy to be released quickly and easily.quickly and easily.
ATP
ATP generationATP generation Cells use oxidation-reduction (redox) Cells use oxidation-reduction (redox)
reactions in catabolism to extract energy reactions in catabolism to extract energy from nutrient moleculesfrom nutrient molecules
This energy is trapped by the generation This energy is trapped by the generation of ATP by phosphorylation of ADPof ATP by phosphorylation of ADP
Oxidation-reduction reactionsOxidation-reduction reactions Oxidation is the removal of electrons from a Oxidation is the removal of electrons from a
moleculemolecule Reduction is the gaining of electrons by a Reduction is the gaining of electrons by a
moleculemolecule Oxidation and reduction reactions are always Oxidation and reduction reactions are always
coupled (redox reaction)coupled (redox reaction)
Many catabolic oxidation-Many catabolic oxidation-reduction reactions are also reduction reactions are also dehydrogenation reactionsdehydrogenation reactions
The removal of electrons also means the The removal of electrons also means the removal of hydrogen atoms [i.e., not just removal of hydrogen atoms [i.e., not just an electron but also a proton (an electron but also a proton (HH++)])]
These are transferred to an “electron These are transferred to an “electron carrier”carrier”
Electron carriersElectron carriers
In catabolic In catabolic reactions, energy is reactions, energy is extracted from extracted from molecules in the molecules in the form of electrons, form of electrons, which are which are transferred, along transferred, along with Hwith H++ ions, to ions, to electron carriers electron carriers like NADlike NAD++. .
2H+ + 2e-
NAD NADH+ + H+
Mechanisms of ATP generationMechanisms of ATP generation
Substrate-level phosphorylationSubstrate-level phosphorylation
Oxidative phosphorylationOxidative phosphorylation
PhotophosphorylationPhotophosphorylation
Substrate-level phosphoryationSubstrate-level phosphoryation
ATP is generated when a high-energy ATP is generated when a high-energy phosphate is transferred directly to ADP phosphate is transferred directly to ADP from a phosphorylated substratefrom a phosphorylated substrate
Oxidative phosphorylationOxidative phosphorylation Electrons are transferred from organic compounds Electrons are transferred from organic compounds
through a series of electron carriers to Othrough a series of electron carriers to O22 or other or other oxidized inorganic or organic moleculesoxidized inorganic or organic molecules
The sequence of electron carriers is called the The sequence of electron carriers is called the electron transport chainelectron transport chain
The transfer of The transfer of electrons from one electrons from one carrier to the next carrier to the next generates energy generates energy which is used to which is used to make ATP from ADP make ATP from ADP byby chemiosmosischemiosmosis
PhotophosphorylationPhotophosphorylation Only occurs in photosynthetic cells which Only occurs in photosynthetic cells which
contain light trapping pigment such as contain light trapping pigment such as chlorophyllchlorophyll
Light causes chlorophyll to give up electronsLight causes chlorophyll to give up electrons
Energy released by Energy released by the transfer of the transfer of electrons from electrons from chlorophyll to carrier chlorophyll to carrier molecules is used to molecules is used to generate ATPgenerate ATP
How do chemoheterotrophs How do chemoheterotrophs generate energy?generate energy?
Sources of energy: carbohydrate, fat, Sources of energy: carbohydrate, fat, protein, minerals.protein, minerals.
Most microorganisms oxidize Most microorganisms oxidize carbohydratescarbohydrates as the major source of as the major source of cellular energycellular energy
Energy can also be derived from the Energy can also be derived from the oxidation of fats, proteins, and minerals.oxidation of fats, proteins, and minerals.
Carbohydrate Carbohydrate catabolismcatabolism
Microbes use two Microbes use two general processes to general processes to generate energy from generate energy from glucoseglucose
Aerobic respirationAerobic respiration FermentationFermentation Both start with Both start with
glycolysisglycolysis
(= Emden Meyerhoff pathway)(= Emden Meyerhoff pathway)
Aerobic RespirationAerobic Respiration Glycolysis (Embden-Meyerhof)Glycolysis (Embden-Meyerhof)
Glucose is oxidized to pyruvic acidGlucose is oxidized to pyruvic acid Pyruvic acid is oxidized to acetyl CoA Pyruvic acid is oxidized to acetyl CoA
TCA cycle (Kreb’s cycle)TCA cycle (Kreb’s cycle) Acetyl CoA is oxidized to COAcetyl CoA is oxidized to CO22
Electron transport chainElectron transport chain Reduced NADH and FADHReduced NADH and FADH22 from the from the
above are oxidized through a series of above are oxidized through a series of redox reactions through an electron redox reactions through an electron transport chain.transport chain.
GlycolysisGlycolysis
Starting point for cellular respiration and Starting point for cellular respiration and fermentation. fermentation.
10 step catabolic pathway10 step catabolic pathway Two stagesTwo stages
Preparatory stagePreparatory stage Energy conserving stageEnergy conserving stage
ADP
Glucose
Glucose6-phosphate
Fructose1,6-diphosphate
Glyceraldehyde3-phosphate
Dihydroxyacetonephosphate
Fructose6-phosphate
ATP
P
ADP
ATP
PP
Glycolysis: preparatory stageGlycolysis: preparatory stage
2 ATPs are used2 ATPs are used Glucose is split to Glucose is split to
form 2 molecules form 2 molecules of Glyceraldehyde-of Glyceraldehyde-3-phosphate3-phosphate
P
P
P
Hexokinase
Phosphoglucoisomerase
Phosphofructokinase
aldolase
Triose phosphate isomerase
ADP
Glyceraldehyde3-phosphate
Diphosphoglyceric acid
ATP
Glycolysis: energy conserving stage Glycolysis: energy conserving stage
For each initial For each initial glucose molecule; glucose molecule;
2 Glyceraldehyde-2 Glyceraldehyde-3-phosphate 3-phosphate oxidized to 2 Pyruvic oxidized to 2 Pyruvic acidacid4 ATP produced4 ATP produced2 NADH produced2 NADH produced
NAD+ NAD+
NADHNADH
P P
P P
PP PP
P P3-phosphoglyceric
acid
ADP
ATP
2-phosphoglyceric acid
P P
P P
H2O H2O
Phosphoenolpyruvic acid
ADP
ATP Pyruvic acid
ADP
ATP
Triose phosphate dehydrogenase
Phosphoglycerokinase
Phosphoglyceromutase
Enolase
Pyruvate kinase
Summary of glycolysisSummary of glycolysis
Glucose (CGlucose (C66HH1212OO66) is split and oxidized ) is split and oxidized through a ten step pathway to two through a ten step pathway to two molecules of pyruvic acid (Cmolecules of pyruvic acid (C33HH44OO33))
Net gain of 2 ATP molecules, 4 from Net gain of 2 ATP molecules, 4 from energy conserving phase (by substrate energy conserving phase (by substrate level phosphorylation) minus 2 from level phosphorylation) minus 2 from preparatory phasepreparatory phase
2 NADH molecules produced2 NADH molecules produced Pyruvic acid can now undergo either Pyruvic acid can now undergo either
fermentation or respirationfermentation or respiration
Alternatives to glycolysisAlternatives to glycolysis
Many bacteria have an alternative Many bacteria have an alternative pathway to glycolysis for the oxidation of pathway to glycolysis for the oxidation of glucoseglucose
Entner-doudoroff reactionEntner-doudoroff reaction Phosphogluconate pathwayPhosphogluconate pathway
Some bacteria oxidize Some bacteria oxidize inorganic inorganic compounds instead of glucose to get compounds instead of glucose to get energy. (energy. (the Lithotrophsthe Lithotrophs))
Use of Use of InorganicInorganic ions as electron ions as electron ““SOURCES”SOURCES” (Lithotrophs)(Lithotrophs)
Bacteria, by Energy sourcesBacteria, by Energy sources
PhototrophsPhototrophs Chemotrophs Chemotrophs
Oxidize organic compounds for Energy:Oxidize organic compounds for Energy:ChemoorganotrophsChemoorganotrophs
Oxidize inorganic compounds for Energy:Oxidize inorganic compounds for Energy:ChemolithotrophsChemolithotrophs