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- oxidation electron donor

(aka energy source)(O2+ 4H+ + 4e- ==> 2H2O) x6 reduction electron acceptor---------------------------------------C6H12O6 + 6 O2 ==> 6 CO2 + 6 H2O overall reaction (24 electrons)

Types of bacterial metabolisms

• While eukaryotes only reduce O2 and oxidize organiccompounds, prokaryotes can use a variety of electrondonors 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?

organiccompound CO2

chemoheterotroph chemoautotroph

e- acceptor?

O2 Other than O2

Organiccompound

Inorganiccompound

fermentative organism anaerobic respiration: nitrate, sulfate, Fe(III)

carbon source?

photoheterotroph photoautotroph

green non-sulfur and purple non-sulfur bacteria anoxygenic

photosynthesis: green sulfur and

purple sulfur bacteria

use H2O to reduce CO2?

oxygenic photosynthesis:cyanobacteria

organiccompound CO2

most bacteria

Nitrifying and sulfur-oxidizing bacteria

Aerobic or anaerobic respiration

Chemolithotrophy

Important molecules

Redox Electron Carrier: for example the NAD/NADH couple

Energy storage compounds: ATPCoenzyme A

NAD as a Redox Electron Carrier

• freely diffusible carrier• nicotinamide-adenine dinucleotide NAD+

• transferring electrons from one place toanother in the cell• carry 2 e- and 2 protons (H+)• NAD+/NADH -0.32 V - NADH is a good e-

donor•NAD+ + 2 e- +2 H+ ==> NADH + H+

2 [H]

Coenzyme A

• Conserve energy released in energy-producingreactions• 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

glucose pyruvate

TCAcycle

glycolysis

lactate

butyrate

acetate

Acetyl-coA

Oxidative phosphorylation

NADH/ FADH2

Proton motive force

ATP

ATPase

GTP Substrate-level phosphorylationATP

Substrate-level phosphorylation

ATP

e- acceptor:O2, NO3

- orSO4

2-

fermentation

NADH

Substrate-level phosphorylation

ATP

CAC= citric acid cycle

Glycolysis

Citric acid cycle

Oxidative Phosphorylation

• NADH and FADH coming fromglycolysis will bring electrons

NADH ==> NAD+ + e-

FADH2 ==> FAD+ + e-

• These electrons are transporteddown the chain until they oxidizeO2

• At each step, protons aretranslocated to outside themembrane

• Thus, a proton gradient isestablished between inside andoutside the cell

• This proton gradient is termed theproton motive force (PMF)

anaerobic respiration

ATP generation with PMF

• The proton motiveforce is used by ATPsynthase to produceATP.

• Process calledchemiosmosis

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 theway.

• Various organisms participate in the degradation of a polymeric sugarsuch as cellulose

time

con

cen

trati

on

cellulose

acetate

CH4

fatty acidsH2

Methanogenic environments

Carbohydrates, nucleic acidsProteins, lipids

1

LactatePropionate

Alcohols, …

AcetateH2, CO2

CH4, CO2

2

3

4

1234

Fermentative bacteria

Syntrophic bacteria

Homoacetogenic bacteria

Methanogenesis

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 co-

culture to remove the H2 produced• Homoacetogenic:4 H2+ H+ + 2 HCO3

- ==> CH3COO- + 4 H2O acetate

• Methanogenic (archea)4 H2+ CO2

==> CH4 + 2 H2Omethane

Sulfidogenic environments

Carbohydrates

1

LactatePropionate

Alcohols, …

AcetateH2, CO2

H2S and CO2 and/or acetate

2

3

123

Fermentative bacteria

Syntrophic bacteria

Sulfate-reducing bacteria

2

SO42-

Important molecules

C C C

O

O

OHpyruvate

lactate

C C O

OH

acetateC C C O

OH

OH

succinateC C C O

OHCO

OH

fumarate

C C C OOH

COOH

C O

OH

formate

C C

OH

ethanol

OH

malate

C C C OOH

CO

OH