week 7 cellular respiration

Introduction to Cellular Respiration and Fermentation

• Part one of a four-part video series by Edward Awad.

• Focus on the role of redox reactions in biology and energy extraction from glucose.

Redox Reactions

• Definition: In redox reactions, energy of electrons transfers between reactants.

  • Oxidation: Loss of electrons or hydrogen atoms.

  • Reduction: Gain of electrons or hydrogen atoms.

• Example: Photosynthesis reaction:

  • Carbon dioxide is reduced (gains electrons) to form glucose.

  • Water is oxidized (loses hydrogen atoms).

• Importance of redox reactions in energy transfer through hydrogen atoms to carbon atoms.

Chemical Bonds and Energy Storage

• Covalent bonds between carbon and hydrogen possess higher potential energy than those between carbon and oxygen.

• Carbohydrates and fats, rich in carbon-hydrogen bonds, store significant potential energy used to produce ATP.

Glucose as a Fuel Source

• Glucose: Primary chemical fuel for cells, crucial for ATP production.

• Processes for glucose oxidation lead to energy capture for ATP synthesis.

• Free Energy: Complete oxidation of glucose yields 686 kilocalories of energy, driving ATP formation.

Electron Carriers

• NAD (Nicotinamide Adenine Dinucleotide): Critical electron carrier in glucose metabolism.

  • Forms: NAD+ (oxidized) and NADH (reduced).

  • NADH oxidation is exergonic, providing energy for ATP formation.

Metabolic Pathways for Glucose Oxidation

1. Glycolysis:

   • Breakdown of glucose into pyruvate occurs in the cytoplasm.

   • Divided into energy-investing and energy-harvesting stages.

   • Produces 2 ATP and 2 NADH from one glucose molecule.

2. Aerobic Respiration:

   • Requires oxygen as the final electron acceptor.

   • Composed of three processes:

     • Pyruvate oxidation.

     • Citric acid cycle.

     • Electron transport chain and oxidative phosphorylation.

3. Fermentation:

   • Occurs under low oxygen conditions.

   • Partial oxidation of glucose with less energy yield, producing lactic acid or ethanol.

Detailed Glycolysis

• Energy-investing stage requires input of ATP to initiate glucose breakdown.

  • Phosphorylation steps lead to the production of G3P (glyceraldehyde 3 phosphate).

• Energy-harvesting stage where G3P is oxidized, producing ATP via substrate-level phosphorylation.

• Net Yield: 2 ATP, 2 NADH, and 2 pyruvate from one glucose.

Pyruvate Processing

• Converts pyruvate into Acetyl CoA in mitochondrial matrix.

• Each glucose produces 2 pyruvate:

  • Produces 2 NADH and 2 CO2.

Citric Acid Cycle (Krebs Cycle)

• Occurs in the mitochondrial matrix for eukaryotic cells; cytoplasm for prokaryotic.

• Involves 8 reactions, producing:

  • 6 NADH,

  • 2 FADH2,

  • 2 ATP (GTP),

  • 4 CO2 from one glucose.

Electron Transport Chain and Oxidative Phosphorylation

• Coupled processes for ATP formation using high-energy electrons from NADH and FADH2.

• Considered the primary energy-producing pathway within aerobic respiration:

  • Protons pumped into intermembrane space create a proton-motive force.

  • ATP synthase uses this force to synthesize ATP from ADP and inorganic phosphate.

• Yield: Approx. 28 ATP from oxidation of glucose per oxidative phosphorylation.

Fermentation Pathways

• Two types exist in anaerobic conditions:

  • Lactic Acid Fermentation: Converts pyruvate to lactate, regenerating NAD+.

  • Alcohol Fermentation: Converts pyruvate to ethanol and CO2, also regenerating NAD+.

Metabolic Interconnections

• Intermediates from glycolysis and citric acid cycle serve as building blocks for synthesizing essential biomolecules.

• Regulation of metabolic pathways through allosteric enzymes governed by feedback inhibition or stimulation:

  • Example: Enzyme control in glycolysis and citric acid cycle based on cellular energy status.