anaerobic respiration

acts as emergency measure for ATP production when oxygen levels low bc doesn’t require oxygen

• involves glycolysis

• at end will have:

  • 2 ATP, 2 reduced NAD + 2 pyruvate

  • need to oxidise nas to allow dehydrogenation reactions in glycolyiss to continue to allow (some) ATP to be produced by substrate level phosphorylation

  • 2 types anaerobic respiration

  • in mammalian muscle + in yeast (and some plant cells)

categories of organisms based on oxygen requirements for metabolic processes

• obligate anaerobes - cannot survive in presence of oxygen

• facultative anaerobes - switch between aerobic + anaerobic respiration, depending on oxygen availability.

• obligate aerobes - depend on oxygen to synthesise ATP

eukaryotic cells can perform either type of respiration depending on situation

alcohol fermentation and lactic acid fermentation

• anaerobic conditions: cells can produce small yield of ATP (glycolysis). can only continue if reduced NAD produced can be oxidised again

• link reaction + Krebs cycle cannot continue if all FAD + NAD are reduced bc they cannot accept any more protons + electrons.

• oxidative phosphorylation cannot occur w out oxygen bc final electron acceptor

• 2 major pathways through which cells can undergo anaerobic respiration: alcohol fermentation + lactic acid fermentation.

If too much anaerobic respiration occurs in muscle tissue, the reduced quantity of ATP produced is insufficient to maintain vital processes for extended time periods. This means lactic acid accumulates, causing cramp and muscle fatigue, and it also reduces the pH affecting enzymes.

some animals muscles + bacteria w out oxygen: lactate fermentation

• glycolysis occurs → pyruvate, 2 reduced NAD + 2 ATP by SLP

• pyruvate (final electron acceptor) accepts electrons (hydrogen) from reduced NAD + reduced to lactate by lactate dehydrogenase

• NAD (re)oxidised so can accept ↑ electrons(hydrogen) from dehydrogenation reactions in glycolysis

• thus glycolysis can continue + produce small amount of ATP

yeast and some plants w out oxygen: alcohol fermentation

• glycolysis occurs → pyruvate, 2 reduced NAD + 2 ATP by SLP

• pyruvate decarboxylated releasing CO₂ + produces ethanal (catalysed by pyruvate decarboxylase)

• ethanal accepts electrons (hydrogen) from reduced NAD + reduced to ethanol by ethanol dehydrogenase

• NAD (re)oxidised so can accept ↑ electrons(hydrogen) from dehydrogenation reactions in glycolysis

• thus glycolysis can continue + produce small amount of ATP

comparing anaerobic respiration