Lecture: Catabolism and Fermentation

Introduction

• Overview of catabolism and fermentation processes.
• Importance in cellular metabolism.

Catabolism

• Definition: Breakdown of complex molecules to form simpler ones.
• Purpose: To release energy stored in chemical bonds.
• Key Points:
  • Involves oxidation-reduction reactions.
  • Energy released used to synthesize ATP.

Fermentation

• Definition: A metabolic process converting sugar to acids, gases, or alcohol.
• Purpose: To regenerate NAD+ from NADH, allowing glycolysis to continue.
• Key Characteristics:
  • Occurs in the absence of oxygen (anaerobic).
  • Less efficient than aerobic respiration.
  • Produces less ATP compared to complete oxidation of glucose.

Types of Fermentation

• Alcoholic Fermentation:
  • End products include ethanol and CO2.
  • Occurs in yeast and some types of bacteria.
• Lactic Acid Fermentation:
  • End product is lactic acid.
  • Occurs in muscle cells, red blood cells, and some bacteria.

Comparison with Respiration

• Aerobic Respiration:
  • Requires oxygen.
  • Produces more ATP.
• Anaerobic Processes:
  • Include both fermentation and anaerobic respiration.
  • Less efficient in ATP production.

Applications of Fermentation

• Food Industry:
  • Production of bread, yogurt, beer, and wine.
• Biotechnology:
  • Production of biofuels, pharmaceuticals, etc.

Extra notes:

Here's a reorganized version of your notes, aiming for improved clarity and structure: **MBI 201 - Catabolism of Sugars (03/21/25)** **I. Microbial Catabolism: The Big Picture** * **Goal:** Obtain energy & building blocks (biomass) from diverse substrates. * **Process:** Break bonds, capture electron energy, release simpler waste products & usable compounds for anabolism. * **Substrates:** Carbohydrates (polysaccharides, monosaccharides, glycans), lipids, proteins/amino acids, aromatic compounds (plant fiber). * **Central Pathways:** Polysaccharides are broken down into monosaccharides, which feed into central catabolic pathways that generate pyruvate. Lipids and amino acids are broken down to glycerol and acetate (acetyl-CoA) & intermediates. Aromatic compounds are catabolized to acetate via pathways like the catechol pathway. These intermediates feed into central pathways, showcasing metabolic commonalities despite microbial diversity. **II. Central Catabolic Pathways** * **Two Main Types:** * **Fermentation:** Partial breakdown; no net electron transfer to an inorganic electron acceptor. * **Respiration:** Complete breakdown; electron transfer to a terminal electron acceptor (e.g., O2, NO3-). **III. Glucose Catabolism: Three Pathways** * Three main routes to catabolize glucose: 1. **Embden-Meyerhof-Parnas (EMP) pathway (Glycolysis):** * Most common; cytoplasm; aerobic & anaerobic. * Ten reactions in two stages: * **Glucose Activation:** Uses 2 ATP; converts glucose to fructose 1,6-bisphosphate. * **Energy-Yielding:** Produces 4 ATP (substrate-level phosphorylation), 2 NADH. Key enzyme: glyceraldehyde 3-phosphate dehydrogenase (G3PDH). Rate-limiting step: Phosphofructokinase (PFK). * Net: 2 ATP and 2 NADH per glucose. 2. **Entner-Doudoroff (ED) pathway:** * Evolutionarily older; diverse prokaryotes. * Fewer substrate phosphorylation steps; produces NADH and NADPH. * Favored by aerobes (less need for maximum ATP from EMP since respiration generates more). 3. **Pentose Phosphate Pathway (PPP):** * Produces 2 NADPH (biosynthesis) and precursor sugars (ribose-5-P, erythrose-4-P, sedoheptulose-7-P) for nucleotide, amino acid, and lipopolysaccharide synthesis. Minimal ATP production. **IV. Pathway Choice** * EMP: Optimal for energy capture (2 ATP, 2 NADH). * ED: Moderate energy (1 ATP, 1 NADH) and biosynthetic precursors (1 NADPH). * PPP: Primarily for biosynthesis (2 NADPH) and precursor synthesis. Choice depends on cellular needs and oxygen availability. **V. Fermentation: Completing Catabolism** * **Definition:** Catabolism without an electron transport chain; NADH reduces pyruvate or derivatives; limited ATP gain. Function: Regenerate NAD+ for continued glycolysis. * **Types:** * **Ethanol Fermentation:** 2 ethanol + 2 CO2 * **Homolactic Fermentation:** 2 lactic acid * **Heterolactic Fermentation:** Variations producing lactic acid, ethanol/acetate, and CO2. * **Mixed Acid Fermentation:** Acetate, formate, lactate, succinate, ethanol, H2, CO2 (proportions vary with pH). **VI. Industrial & Clinical Applications** * Fermentation products used in food processing (yogurt, cheese, sauerkraut, etc.) and industrial applications (solvents, biofuels). * Fermentation tests aid in identifying infectious microbes. Example: Sorbitol fermentation distinguishes *E. coli* O157:H7 from other strains. **VII. Summary** * Fermentation completes catabolism without an electron transport chain. * Regenerates NAD+ for continued glycolysis; limited ATP production. * Diverse fermentation pathways exist; products useful industrially and clinically. This structure provides a logical flow, categorizing information for better comprehension. Remember to review and add any details you find crucial to your understanding.

Conclusion

• Summary of the role of catabolism and fermentation in energy production.
• Importance in both natural ecosystems and industrial applications.