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