3.3: Anaerobic Respiration and Fermentation

Anaerobic Respiration

  • metabolic pathway in which inorganic molecules other than O2 used as final e acceptor during chemiosmotic ATP synthesis

    • SO4, NO3, CO3

  • cells have limited NAD+

    • NADH by glycolysis oxidizes NAD+

  • fermentation only produced same number of ATP as glycolysis

    • less efficient than aerobic

Prokaryotic Anaerobic Respiration

  • lack mitochondria

  • contain ETCs on plasma membrane

  • uses inorganic chemical compounds as e acceptors

E. Coli

  • bacteria carreeis out aerobic and anaerobic

  • when anaerobic, use nitrate reductase as e acceptor from ETC

Methanogens

  • use ETC, generate H+ gradient for phosphorylation

  • use H2 synthesized by other organisms as energy source

  • CO2 as electron acceptor

  • common in marshes, wetlands, intestines

  • release methan

Fermentation

  • performed by yeasts, bacteria, humans

  • anaerobic

  • gycolysis

  • alternate pathway for NADH oxidation to NAD+ (re used in glycolysis)

  • organic molecule as final e acceptor

Lactate Fermentation

  • supplemental energy pathway in eukaryotes

  • occurs in muscle cells when ATP demand is greater than O2 supply

  • excess pyruvate —> lactate, regenerates NAD+ (can go back to glycolysis)

  • lactic acid accumulates in muscle cells

  • oxygen debt = O2 required to eliminate lactate

    • lactate oxidized to pyruvate

    • some turned into glycogen in muslces

  • less efficient

    • pyruvate —> 2 lactate + 2 ATP

  • lactate threshold = pain during exhaustive all-out exercise in which lactate builds up in bloodstream faster than can remove it

  • deep breaths diminish O2 debt

Types of Muscle Fibres

  • slow oxidative = contract slowly, tire out slowly

    • many mitochondria

    • allow for sustained postures or movement

    • use oxidation of fatty acids and amino acids

  • fast-glycolytic fibres = contract rapidly, tire out rapidly

    • few mitochondria

    • powerful, quick movements

    • ATP comes from glycolysis

Lactate Fermentation Applications

  • lactic acid is sour

  • bacteria produce as fermentation product

  • make buttermilk, yogurt, dill pickles, cheese

Alcohol/Ethanol Fermentation

  • yeast and other bacteria are aerobic and anaerobic

    • facultative anaerobes

  • pyruvate decarboxylated into acetyl aldehyde

  • acetyl aldehyde used to oxidize NADH to NAD+

  • ethanol produced as waste product

  • pyruvate —> 2 ethanol + 2 CO2 + 2 ATP

Applications of Ethanol Fermentation

  • yeast (CO2 produced)

  • brew beer and wine

  • high commercial value

Ethanol Fermentation and Fuel Production

  • chemical energy of glucose stays in compounds formed from glycolysis

    • products used for fuel

  • ethanol produced as toxic waste product

    • 12% concentration gradient causes death in yeast cells

  • ethanol can be burned

    • fuel lamps (1800s)

    • fuel early internal combustion engines in cars and machinery (1800s)

  • gasoline used to cost less than cost to produce ethanol

    • increased gas prices, investing in bio fuels

    • most auto engines use E10

    • E85 used by flex fuel vehicles

How Ethanol Fuel is Made

  • fermentation of corn and wheat

    • product = “beer”, 10% ethanol and 90% water

  • distilling “beer” eliminates water to yield pure ethanol

  • small amounts of gas added to make unfit for human consumption

  • solid residues from grain and yeast dried to produce DOGS

    • DOGS = vitamin and protein rich product, distillers dried grains and solubles

    • livestock feed