8.4.pdf

Many cells can’t perform respiration due to: Lack of Final Electron Acceptor: The cell doesn't have enough of the right inorganic final electron acceptor needed for respiration. Genetic Limitations: ○ The cell lacks genes to make necessary complexes and electron carrie...

Many cells can’t perform respiration due to: Lack of Final Electron Acceptor: The cell doesn't have enough of the right inorganic final electron acceptor needed for respiration. Genetic Limitations: ○ The cell lacks genes to make necessary complexes and electron carriers for the electron transport system. ○ The cell lacks genes for enzymes required in the Krebs cycle. Key Points: The inability to use an inorganic final electron acceptor depends on the environment, while the genetic issues are permanent. Some prokaryotes (e.g., Streptococcus) cannot respire at all, even with oxygen. Many prokaryotes are facultative: they can switch to respiration if conditions allow, increasing ATP production per glucose. Without respiration, NADH must be recycled to NAD+ for glycolysis, the only way to produce ATP. Some organisms use organic molecules (like pyruvate) as a final electron acceptor in fermentation: ○ Fermentation does not involve the electron transport system. ○ It produces only up to 2 ATP per glucose during glycolysis. Microbial Fermentation: Humans use fermentation to produce foods, pharmaceuticals, and to identify microbes. Lactic Acid Fermentation: Involves bacteria like those in yogurt and muscle cells during low oxygen. Chemical Reaction: ○ Pyruvate + NADH ↔ Lactic Acid + NAD+ Lactic Acid Bacteria (LAB): ○ Includes Lactobacillus, Leuconostoc, and Streptococcus. ○ Important in making yogurt and cheese by solidifying milk proteins through acidity. Types of Fermentation: ○ Homolactic Fermentation: Only lactic acid produced (e.g., Lactobacillus delbrueckii). ○ Heterolactic Fermentation: Produces lactic acid, ethanol, acetic acid, and CO2 (e.g., Leuconostoc mesenteroides for pickles and sauerkraut). Medical Importance of LAB: Help prevent pathogen growth by maintaining low pH in the body. Important for vaginal health; imbalance can lead to yeast infections. Key component of probiotics for gastrointestinal health. Alcohol Fermentation: Produces ethanol. Chemical Reaction: ○ Pyruvate → Acetaldehyde + CO2 (by pyruvate decarboxylase). ○ Acetaldehyde + NADH → Ethanol + NAD+ (by alcohol dehydrogenase). Used in making alcoholic beverages and baking (CO2 makes bread rise). Important for biofuel production from plant products. Key Points: Various fermentation methods in prokaryotes maintain NAD+ for glycolysis. Without fermentation, glycolysis wouldn’t occur, and ATP wouldn’t be produced. Most fermentation types (except homolactic) produce gases (CO2, hydrogen). Fermentation is important for food production, creating unique flavors. ○ Example: Propionic acid gives Swiss cheese its flavor. Commercial fermentation products: ○ Acetone and butanol from acetone-butanol-ethanol fermentation. ○ Complex organic compounds for antibiotics and vaccines from mixed acid fermentation. Fermentation products help identify bacteria in labs: ○ Enteric bacteria perform mixed acid fermentation (lowers pH). ○ Gas production detected in inverted Durham tubes. Differentiation of microbes based on fermentation: ○ E. coli ferments lactose (produces gas); some relatives do not. ○ O157 strain of E. coli cannot ferment sorbitol. ○ Mannitol fermentation distinguishes Staphylococcus aureus from others.