L13 Anaerpbic energy

Energy without oxygen

1. alternative respiratory chains

   1. non-NADH donors

   2. Anaerobic respiration (non-O2 acceptors)

2. Fermentation

Oxygen (electron acceptor)

• oxygen is the perferred electron acceptor due to its extremely hgih redox potential

  • max ATP production

Common ETC characteristics

1. starts with low potential (E naut ‘) substrates

2. They end with higher potential substrates

3. They employ electron carrier molecules

4. They contribute to the PMF

   1. “start low→ end high”

Respiration - Donors

• NADH

• Lactate

• Hydrogen

• Formate

• alpha-Gly-P

• succinate

Respiration - Acceptors

• O2

• Nitrate

• Fe3+

• DMSO

• TMANO

• Fumarate

Paracoccus dentrificans + O2

• Grows aerobically NADH→O2

• Usually NADH→O2 for anaerobic

  • yields 4 protons vs 6

Other electron acceptors - Oxidized metals

• Fe3+→Fe2+: +771mV

• Mn4+→Mn2+: +588mV

Other electron acceptors - Oxidized organic compounds

• DMSO→DMS: +771mV

• TMANO→TMA: +130mV

• Fumarate→Succinate: +30mV

Geobacter and ferric Iron

…

Campylobacter Jejuni

• use molecular hydrogen and formate as donors

• Can use O2, Nitrate, DMSO as acceptors

Wollinella succinogenes (obligate anaerobe)

…

Pyrcoccus Furiosus

• Archaeon lives in “black smokers” on the ocean floor

• Environment: Hot (P. furiosus can grow up to 110C)

  • high organic content

  • highly reducing

  • no O2

• Starts with reduced ferredoxin as donor

  • ends with reduced hydrogen as acceptor

Fermentation

• If you gave no e- acceptor, electron transport stops

• Electron transport chains gets “backed up”

  • all the components are reduced and connot be re-oxidized

• Must rely on substrate level phosphorylation for all your ATP requirements

Fermentations (basics)

1. produces various substances

2. NADH is consumed and NAD+ is produced

   1. allows glycolysis to continue

3. Substrate is pyruvate

4. Made up of oxidation/reduction reactions

NADH becomes a problem

• Reducing potential stored aas NADH can only be harvested if an electron acceptor is availble

• NAD+ must be regenerated it is needed in glycolysis as well as other biosynthetic pathways

• TCA stops (as a cycle), because it is creating more of problem (4NADH)

• Glycolysis becomes the main energy generator (2ATP/glucose), but the cells still requires the 2 NAD+ to reduce to NADH in order for glycolysis to operate

Eukaryotic Fermentation (2 results)

• Alcoholic fermentation:ethyl alcohol

• Lactic acid fermentation: lactic acid

Microbial Fermentation products

• Lactic acid

• ehtanol & Co2

• hydrogen

• butanol and acetone

• acetic acid (vinegar)

• Butyric acid (rancid butter, vomit, body odor)

Lactic acid production

1. reduce pyruvate directly to lactate with NADH oxidation

2. important in making yogurt, cheese, and sausage

3. Utilized as probiotics (commensal)

Normally live in our GI tract

Ethanol production

1. oxidation of NADH to acetaldehyde and then to ethanol

2. Important for making beer and wine

Hydrogen production

• is a byproduct of acetic acid fermentation

• Important in fuel cell technology and sustainable energy

Bioreactors

• Using bacteria in reactors to make hydrogen

• Problems:

  • reactor must stay anaerobic

  • bacteria need sugar

  • must be a monoculture of H producers

  • difficult to keep large cultures Pure