NutCultCatab II

7/17/2019 NutCultCatab II

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Nutrition, Culture, and

Metabolism of Microorganisms,

Part II

01-27-15



IV. Essentials of Catabolism

• 3.8 Glycolysis

• 3.9 Fermentative Diversity and the

Respiratory Option

• 3.10 Respiration: Electron Carriers

• 3.11 Respiration: The Proton Motive Force

• 3.12 Respiration: Citric Acid Cycle

• 3.13 Catabolic Diversity



3.8 Glycolysis

•Two reaction series are linked to energyconservation in chemoorganotrophs:

fermentation and respiration

•

Differ in mechanism of ATP synthesis – Fermentation: substrate-level

phosphorylation; ATP directly synthesized

from an energy-rich intermediate

– Respiration: oxidative phosphorylation; ATP

produced from proton motive force formed by

transport of electrons



Energy-rich

intermediates ADP

BA B P P DC~ ~

P i

Substrate-level phosphorylation

Oxidative phosphorylation

ADP P i

Energizedmembrane

Less energized

membrane

Dissipation of proton

motive force coupled

to ATP synthesis

+

ATP

ATP



3.8 Glycolysis

• Fermented substance is both an electrondonor and an electron acceptor

• Glycolysis (Embden-

Meyerhof pathway): acommon pathway for catabolism of glucose

– Anaerobic process

– Three stages

• Overview

–Glucose consumed

– Two ATPs produced

– Fermentation products generated• Some harnessed by humans for consumption





3.9 Fermentative Diversity and the

Respiratory Option

• Fermentations classified by products

formed

– Ethanol

– Lactic acid

– Propionic acid

– Mixed acids

– Butyric acid

– Butanol



3.9 Fermentative Diversity and the

Respiratory Option

• Fermentations classified by substratefermented – Usually NOT glucose

–

Amino acids – Purines and pyrimidines

– Aromatic compounds

• Saccharomyces cerevisiae can carry out

fermentation or respiration – Carries out the one most beneficial

• Respiration generates more ATP

• Fermentation occurs when conditions are anoxic



3.10 Respiration: Electron Carriers

• Aerobic Respiration – Oxidation using O2 as the terminal electron

acceptor

–Higher ATP yield than fermentations

• ATP produced at the expense of the proton motive

force, which is generated by electron transport




• Electron Transport Systems – Membrane associated

– Mediate transfer of electrons

–

Conserve some of the energy released duringtransfer and use it to synthesize ATP

– Many oxidation –reduction enzymes areinvolved in electron transport•

NADH dehydrogenases• flavoproteins

• iron –sulfur proteins

• cytochromes




Isoalloxazine ring

Ribitol

Oxidized (FMN)

Reduced (FMNH2)

E 0′ of FMN/FMNH2 (or FAD/FADH2) = – 0.22 V

• NADH dehydrogenases

– proteins bound to inside surface of cytoplasmicmembrane

– active site binds NADH and accepts 2 electrons

and 2 protons that are passed to flavoproteins• Flavoproteins

– contains flavin prostheticgroup (e.g., FMN, FAD)

that accepts 2 electronsand 2 protons butonly donates theelectrons to the next

protein in the chain



Porphyrinring

Pyrrole

Heme (a porphyrin)

Histidine-N

Cysteine-S

Amino acid Amino acid

S-Cysteine

N-Histidine

Protein

Cytochrome


•

Cytochromes – Proteins that contain

heme prosthetic

groups

– Accept and donate a

single electron via

the iron atom

in heme



Cysteine

Cysteine

Cysteine

Cysteine

Cysteine

Cysteine

Cysteine

Cysteine


•

Iron –

Sulfur Proteins – Contain clusters of iron

and sulfur

• Example: ferredoxin

– Reduction potentials

vary depending on

number and position of

Fe and S atoms – Carry electrons



Oxidized

Reduced


• Quinones

– Hydrophobic non-protein-containing

molecules that participate in electron

transport

– Accept electrons andprotons but pass

along electrons

only



3.11 Respiration: The Proton Motive Force

• Electron transport system oriented incytoplasmic membrane so that electronsare separated from protons

• Electron carriers arranged in membrane inorder of their reduction potential

•

The final carrier in the chain donates theelectrons and protons to the terminalelectron acceptor





3.11 The Proton Motive Force

• During electron transfer, several protonsare released on outside of the membrane

– Protons originate from NADH and thedissociation of water

• Results in generation of pH gradient and anelectrochemical potential across themembrane (the proton motive force)

– The inside becomes electrically negative andalkaline

– The outside becomes electrically positive andacidic



CYTOPLASM E N V I R O N M E N

T

Complex II

Succinate

Fumarate

Qcycle

0.22

0.0

0.1

0.36

0.39

E 0(V)

E 0(V)

3.11 The Proton Motive Force• Complex I ( NADH:quinone

oxidoreductase) – NADH donates e to FMN

– FMNH2 donates e to quinone

• Complex II (succinate dehydrogenasecomplex)

– Bypasses Complex I – Feeds e and H+ from FADH directly to

quinone pool

• Complex III (cytochrome bc 1 com plex) – Transfers e from quinones to

cytochrome c – Cytochrome c shuttles e to

cytochromes a and a3

• Complex IV (cytochromes a and a3 ) – Terminal oxidase; reduces O2 to H2O



MembraneOut

In

F1

Foc12

b2

a

3.11 The Proton Motive Force

• ATP synthase (ATPase):complex that convertsproton motive force into ATP

• Two components – F 1: multiprotein

extramembrane complex,faces cytoplasm

– Fo: proton-conductingintramembrane channel

• Reversible; dissipatesproton motive force



3.12 The Citric Acid Cycle

•Citric acid cycle (CAC): pathway throughwhich pyruvate is completely oxidized toCO2

– Initial steps (glucose to pyruvate) same as

glycolysis – Per glucose molecule, 6 CO2 molecules

released and NADH and FADH generated

– Plays a key role in catabolism and

biosynthesis• Energetics advantage to aerobic

respiration







3.12 The Citric Acid Cycle

• The citric acid cycle generates manycompounds available for biosynthetic purposes

– -Ketoglutarate and oxalacetate (OAA):

precursors of several amino acids; OAA also

converted to phosphoenolpyruvate, a precursor

of glucose

– Succinyl-CoA: required for synthesis of

cytochromes, chlorophyll, and other tetrapyrrolecompounds

– Acetyl-CoA: necessary for fatty acid biosynthesis



3.13 Catabolic Diversity

• Microorganisms demonstrate a wide rangeof mechanisms for generating energy

– Fermentation

– Aerobic respiration – Anaerobic respiration

– Chemolithotrophy

–

Phototrophy



Electron donor

(organic compound)

Organic e –

acceptors

Electron

acceptors

Electron

acceptors

Light

Fermentation

C h e m o t r o p h s

Aerobic

respiration

Anaerobic respiration

Chemoorganotrophy

Anaerobic respiration

Aerobic respiration

Chemolithotrophy

P h o t o t r o p h s

Electron

transport

Generation of pmf

Organic

compound

Cell materialCell material

Photoheterotrophy Photoautotrophy

Phototrophy

Electron transport/

generation of pmf

Electron transport/

generation of pmf




• Anaerobic Respiration – The use of electron acceptors other than

oxygen• Examples include nitrate (NO3

), ferric iron

(Fe3+), sulfate (SO42), carbonate (CO32

),certain organic compounds

– Less energy released compared toaerobic respiration

– Dependent on electron transport,generation of a proton motive force, and

ATPase activity




• Chemolithotrophy – Uses inorganic chemicals as electron donors

• Examples include hydrogen sulfide (H2S), hydrogengas (H2), ferrous iron (Fe2+), ammonia (NH3)

– Typically aerobic – Begins with oxidation of inorganic electron

donor

– Uses electron transport chain and protonmotive force

– Autotrophic; uses CO2 as carbon source




• Phototrophy : uses light as energysource

– Photophosphorylation: light-mediated ATP

synthesis – Photoautotrophs: use ATP for assimilation

of CO2 for biosynthesis

– Photoheterotrophs: use ATP for

assimilation of organic carbon for

biosynthesis

NutCultCatab II

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