Anaerobic Respiration

Anaerobic Environments

Anaerobic Environments include:

• human gut

• wet environments (swamps)

• Deep underground

• Deep oceans

• landfills

No oxygen present

Anaerobic Pathway

Anaerobic Pathways are processes by which cells can extract energy from glucose and generate ATP without oxygen ~ glycogen

• Two types:

  • Fermentation (No ETC)

  • Anaerobic respiration (has ETC, but oxygen is not the terminal acceptor - last acceptor of ETC)

Prokaryotic Cells

*Has glycolysis and ETC

• But no mitochondria

  • ETC located on plasma membrane

• Some use oxygen as final acceptor (aerobic)

  • Others use sulfate, nitrate, or iron ions as the final acceptor (anaerobic)

• Still no Krebs or pyruvate oxidation in anaerobes

Problem

• Sometimes NADH in glycolysis cannot be reoxidized by ETC fast enough

  • Cells could run out of NAD+, causing glycolysis to stop

Solution

• Fermentation: cellular respiration pathway that transfers electron from NADH to an organic molecule

  • pyruvate or one of its derivatives

• But much less effecient

Alcohol Fermentation

Carried out by yeast

• pyruvate + 2NADH + 2 h+ > 2CO2 + 2NAD+ + 2 ethanol

  • pyruvate gets decarboylated, turning into one of it’s derivatives (acetaldehyde). Here, NADH gets oxidized by the pyruvate derivative

Lactate Fermentation

• Occurs in muscle cells of animals when strenuous activity causes a demand for ATP that exceeds the rate at which oxygen can be supplied to the ETC for oxidative phosphorylation

  • 2 pyruvate + NADH + 2 NADH + 2H+ > 2NAD+ + lactate