Biochemistry: Biomolecules - Cellular Respiration, Fermentation, and Yeast Encapsulation

Introduction to Biochemistry: Biomolecules

Overview

  • The material covers cellular respiration, fermentation, and a lab session focused on encapsulating yeast to induce anaerobic fermentation.

Catabolism and Anabolism

  • Catabolism: Larger molecules are broken down into smaller molecules, releasing energy.
    • Example: Cellular respiration.
  • Anabolism: Smaller molecules are used to build larger molecules, requiring energy.
    • Example: Proteins are synthesized from amino acids.
  • Examples of molecule conversions:
    • Proteins to amino acids
    • Lipids to glycerol, fatty acids
    • Polysaccharides to monosaccharides

Cellular Respiration

  • Aerobic Respiration: Breakdown of food molecules to CO2 and H2O with ATP production, consuming oxygen. Occurs in some prokaryotes, protists, and higher eukaryotes.
  • Anaerobic Respiration: Similar to aerobic but occurs in the absence of oxygen. Found in some prokaryotes.

Aerobic Respiration of Glucose

  • Overall process:
    C6H{12}O6 + 6 O2 \rightarrow 6 CO2 + 6 H2O + \text{energy (in ATP)}
  • Oxidation: Glucose is oxidized.
  • Reduction: Oxygen is reduced.
  • Location:
    • Glycolysis: Cytoplasm
    • Krebs Cycle: Mitochondrion
    • Electron Transport Chain: Mitochondrion
  • ATP Production:
    • Glycolysis: 2 ATP
    • Krebs Cycle: 2 ATP
    • Electron Transport Chain: 34 ATP
  • Anaerobes do glycolysis. They do not perform Krebs cycle or electron transport chain.

Fermentation and Anaerobic Respiration

  • Fermentation: Anaerobic process without an electron transport chain.
    • Regenerates NAD^+ by reducing an organic molecule.
    • Uses substrate-level phosphorylation to generate ATP.
  • Types of Fermentation:
    • Alcohol Fermentation
    • Lactic Acid Fermentation
  • Anaerobic respiration uses an electron transport chain in the absence of oxygen and is distinct from fermentation.

Alcohol and Lactic Acid Fermentation

  • Alcohol Fermentation:
    • Glucose undergoes glycolysis to produce 2 pyruvate molecules.
    • 2 pyruvate molecules are converted to 2 acetaldehyde molecules, releasing 2 CO_2 molecules.
    • 2 acetaldehyde molecules are reduced to 2 ethanol molecules, regenerating 2 NAD^+.
    • Net ATP production: 2 ATP (from glycolysis)
  • Lactic Acid Fermentation:
    • Glucose undergoes glycolysis to produce 2 pyruvate molecules.
    • 2 pyruvate molecules are reduced to 2 lactate molecules, regenerating 2 NAD^+.
    • Net ATP production: 2 ATP (from glycolysis)

Lab Session: Encapsulating Yeast

  • Objective: To deprive yeast of oxygen to observe fermentation.
  • Method: Cross-linking of alginate in the presence of Ca^{2+} to encapsulate yeast cells.

Materials

  • Yeast extract
  • Sodium alginate
  • Dry yeast
  • 20% sucrose solution
  • 0.36 M CaCl_2
  • Pasteur pipette
  • Magnetic bead
  • Beater
  • Sieve
  • Balloon
  • Distilled water
  • Hot plate

Procedure

  1. Rehydrating the Yeast:
    • Resuspend 4 sachets of dry yeast in 50 mL of distilled water.
    • Mix using a Pasteur pipette.
  2. Suspending Yeast in Alginate Solution:
    • Add sodium alginate powder to 100 mL of distilled water to create a 2% (w/v) solution.
    • Mix with a beater until a homogeneous solution is obtained.
    • Add 1% (w/v) yeast extract to the alginate solution.
    • Add the rehydrated dry yeast to the alginate mixture while stirring.
  3. Making Alginate Beads:
    • Prepare 200 mL of 0.36 M CaCl_2 solution.
    • Add drops of the yeast/alginate mixture to the CaCl_2 solution using a Pasteur pipette (with the end cut off), one drop at a time, to form beads.
    • Leave the beads in the CaCl_2 solution for 5 minutes to harden as alginate ionically cross-links with calcium ions.
    • Separate the beads from the solution using a sieve.
  4. Starting the Fermentation Process:
    • Prepare 100 mL of a 20% (w/v) sucrose solution in distilled water, adjusted to pH 5.
    • Add 40 g of the alginate beads to 100 mL of the sucrose solution in an Erlenmeyer flask.
    • Stir at a very low pace and adjust the temperature to 30-40°C.
    • Attach a balloon on top of the Erlenmeyer flask to capture the CO2 produced.
  5. Monitoring the Fermentation Process:
    • Observe for alcohol smell and the appearance of CO_2 bubbles in the solution and balloon inflation.

Introduction to Biochemistry Biomolecules - Fermentation

  • Fermentation: An anaerobic process that doesn't involve an electron transport chain; ATP is generated by substrate-level phosphorylation.
  • Saccharomyces cerevisiae (baker’s yeast) ferments carbon sources under anaerobic conditions, metabolizing glucose to ethanol.
  • Entrapment within sodium alginate is used to immobilize cells without damaging them.
  • The alginate solution mixed with yeast is dripped into a calcium solution, forming beads where yeast is immobilized.
  • Sucrose is added to start fermentation which will produce ethanol and CO_2.

Lab Report Questions

  1. Goal: What is the goal of today’s experiment?
  2. Material and Methods: How do we work? What will we do to create an oxygen-deprived environment? How will we start fermentation?
  3. Results: What is happening? What can you observe?
  4. Discussion: What are the bubbles and why are they formed? Why does the balloon inflate? What is happening to the sucrose solution?
  5. Conclusion: What are the end products of the fermentation process? Why?