Fermentation & Anaerobic Cell Respiration

Fermentation Overview

• Fermentation, lipid catabolism, protein catabolism, and biochemical tests are key topics
• Alcohol and lactic acid fermentation learning targets include knowing where it occurs in cellular respiration
• Targets also include knowing what is being used and produced, and how much ATP is produced

Anaerobic Cell Respiration

• Fermentation is a type of anaerobic cell respiration that releases energy from organic compounds such as sugar
• Oxygen is not required for fermentation
• Organic molecules serve as the final electron acceptor
• A small amount of ATP results from fermentation
• Glycolysis is the cellular respiration step/pathway used
• The Krebs Cycle and Electron Transport Chain are not used
• End products vary depending on the fermentation cycle
• Organic acids or alcohol, like lactic acid, are common end products
• Carbon dioxide is another end product

Importance of Fermentation

• Glycolysis produces a small amount of ATP
• Fermentation is important because oxygen is not always present
• Organisms require sustainable energy production
• Fermentation recycles coenzymes (oxidizes them) so Glycolysis can continue

Alcohol Fermentation Specifics

• A bacterium actively performing alcohol fermentation produces zero ATP in the fermentation step/pathway

Fermentation Examples

• Lactic acid fermentation starts with glycolysis
• Next, pyruvate is broken down into lactic acid
• The fermentation step then oxidizes the reduced coenzyme
• Lactic acid fermentation is important for food preservation
• Lactobacillus species, such as acidophilus which causes milk spoilage, are used in yogurt, sauerkraut, and pickles
• Streptococcus species are plaque formers, and fermentation can cause tooth decay

Alcohol Fermentation Details

• Alcohol fermentation starts with glycolysis
• Next, pyruvate is broken down into acetaldehyde and CO2
• Acetaldehyde is then converted to alcohol
• The fermentation step oxidizes the reduced coenzyme
• Saccharomyces cerevisiae is commonly used
• Saccharomyces cerevisiae is a eukaryote, single-celled fungi (yeast), and baker's yeast or bread yeast

Alcohol Fermentation Significance

• Alcohol fermentation is important in the food industry for bread and beer production
• It is also important in gasohol production

Biochemical Tests - Fermentation

• A biochemical test for fermentation includes a single carbohydrate, a pH indicator, and a Durham tube

Lipid Catabolism

• Fats are good storage molecules containing lots of energy
• Fats are broken down using the enzyme lipase into fatty acids and glycerol
• Fatty acids are oxidized to Acetyl CoA, which enters the Krebs cycle
• Glycerol is broken down, entering glycolysis to produce pyruvic acid, then Acetyl CoA, which enters the Krebs cycle

Protein Catabolism

• Proteins are first broken down into amino acids by exoenzyme protease and peptidase
• Proteases are used as exoenzymes for digestion outside of the cell
• Amino acids are transported across the plasma membrane
• Amino acids are then enzymatically converted, entering cell respiration at several points
  • Deamination - removes an amino group from an amino acid
  • Decarboxylation - removes COOH
  • Dehydrogenation - removes H

Biochemical Tests and Bacterial Identification

• Biochemical tests are used to identify bacteria based on the enzymes they possess
• This is one of the oldest testing methods
• The presence or absence of microbe growth or chemical reaction creates a biochemical fingerprint
• Comparing test strain reactions to known species reactions determines the identity of a microbe