4.4 Anaerobic Pathways

Fermentation

• Not considered a form of respiration
• Low oxygen, abundant glucose
• Perform glycolysis, produce 2 ATP and 2 NADH
  • Must regenerate NAD+ to accept H, or glycolysis cannot continue so NADH must be turned back into NAD+ using an organic compound as an oxidizing agent
  • Cannot use ETC due to lack of oxygen (electron acceptor)
  • Uses organic molecule as oxidizing agent
  • There is a striking difference between the small amount of free energy that is released by this fermentation pathway and the amount released during aerobic cellular respiration.
  • x19 more energy through aerobic than fermentation
• There are 2 types, in some they are primary in others that are backups

Alcohol Fermentation

• Bacteria, yeast
• Pyruvate from glycolysis is decarboxylated to produce acetaldehyde, which oxidizes NADH → NAD+
  • Produces CO2 and ethanol
• Pyruvate + NADH + H+ → NAD+ + CO2 + Ethanol
• glucose + 2 ADP + 2 Pi → 2 ATP + 2 CO2 + 2 ethanol
• Applications:
  • Baking
  • Saccharomyces cerevisiae makes bread dough rise
  • CO2 makes bread rise
  • Ethanol evaporates
  • [[Bread rises because CO2 is released and the spongy look of bread is from where the bubbles were… So when I mix batter more for more bubbles its because..?[[
  • Beer & Wine
  • Rotting fruit

Lactate Fermentation

• Primary energy pathway in prokaryotes
• a process in which pyruvate reacts with NADH and is converted directly into lactate and regenerates NAD+
• Used in eukaryotes when oxygen demand exceeds supply (strenuous exercise)
• NADH continues to be produced in glycolysis, needs to be oxidized back to NAD+
• Excess pyruvate can oxidize NADH and is converted to lactic acid
  • Converted back to pyruvate in liver when oxygen levels normalize (within an hour)
• pyruvate + NADH + H+ → NAD+ + lactate
• glucose + 2 ADP + 2 Pi → 2 lactate + 2 ATP
• [[Onions and lettuce right around fall?[[
• The point at which lactate production is too high for transport out of muscles to keep up is called the lactate threshold. This value can be increased by individuals through training, and it is useful for setting exercise intensity limits in endurance sports.
• The process of lactate fermentation results in an oxygen debt. By taking deeper and more frequent breaths, the body brings in large quantities of oxygen to diminish the oxygen debt.

Anaerobic Respiration

• Similar to aerobic but final electron acceptor is not oxygen but other inorganic molecule

• Prokaryotes

• Alternative ETC along cell membrane

• Uses other electron acceptors

  • Fe3+, NO3, SO42-

• Common in soils, marshes, bogs, etc

• Instead of water, produce hydrogen sulfide (rotten egg smell)

• }}%%Respiration pathways use electron transport systems to generate ATP by oxidative phosphorylation (but without the oxygen, inorganic instead). Fermentation pathways lack such transport systems (just use a different final acceptor, organic).%%}}

• }}%%Anaerobic respiration uses an inorganic substance other than oxygen as the final oxidizing agent. Fermentation relies on an organic compound.%%}}