Cellular Respiration and Fermentation — ATP, Glycolysis, and Energy Pathways Explained | Chapter 9 of Campbell Biology

Cellular Respiration and Fermentation — ATP, Glycolysis, and Energy Pathways Explained (Chapter 9)

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Welcome to Last Minute Lecture! This post covers the essential processes of cellular respiration and fermentation as presented in Chapter 9 of Campbell Biology. Learn how cells harvest energy from glucose, generate ATP, and survive when oxygen is scarce. Watch the full video summary below and subscribe for clear, chapter-by-chapter science explanations!

Introduction: How Cells Extract Energy

Cells rely on complex biochemical pathways to extract energy from organic fuels, primarily glucose, in order to synthesize ATP—the universal energy currency. Chapter 9 details three main stages of cellular respiration: glycolysis, the citric acid cycle, and oxidative phosphorylation. It also explains how fermentation enables ATP production when oxygen is limited.

Overview of Cellular Respiration

  • Catabolic Pathway: Cellular respiration breaks down organic molecules, releasing energy in a controlled, stepwise manner.
  • Aerobic vs. Anaerobic: Aerobic respiration requires oxygen and is highly efficient. Anaerobic respiration and fermentation provide alternate pathways when oxygen is unavailable.
  • Fermentation: Partial degradation of glucose that occurs without oxygen or an electron transport chain.

The Three Stages of Cellular Respiration

  • Glycolysis (Cytoplasm):
    • Splits glucose (6C) into two pyruvate (3C) molecules.
    • Net yield: 2 ATP, 2 NADH, and 2 pyruvate per glucose.
    • Occurs in both aerobic and anaerobic conditions; does not require oxygen.
  • Pyruvate Oxidation & Citric Acid Cycle (Mitochondria):
    • Pyruvate is converted to acetyl CoA, releasing CO₂ and generating NADH.
    • The citric acid cycle (Krebs cycle) produces 2 ATP, 6 NADH, and 2 FADH₂ per glucose and releases CO₂.
    • High-energy electrons are transferred to NADH and FADH₂ for oxidative phosphorylation.
  • Oxidative Phosphorylation (Mitochondrial Inner Membrane):
    • Electron Transport Chain (ETC): Electrons from NADH and FADH₂ are passed through protein complexes, releasing energy.
    • Oxygen is the final electron acceptor, forming water (H₂O).
    • Chemiosmosis: A proton gradient drives ATP synthase, producing about 26-28 ATP per glucose. This step accounts for most cellular ATP production.

Fermentation and Anaerobic Respiration

  • Anaerobic Respiration: Uses an electron transport chain with an alternative final electron acceptor (not oxygen).
  • Fermentation: Only involves glycolysis. NAD⁺ is regenerated to sustain glycolysis when oxygen is lacking.
    • Alcohol Fermentation: Pyruvate is converted to ethanol and CO₂ (in yeast and brewing).
    • Lactic Acid Fermentation: Pyruvate is reduced to lactate (in muscle cells and yogurt production).
  • ATP Yield: Aerobic respiration produces about 32 ATP per glucose; fermentation yields only 2 ATP per glucose.

Redox Reactions and Energy Harvesting

  • Redox Reactions: Electron transfers (oxidation-reduction) release stored energy, driving ATP production.
  • Electron Carriers: NADH and FADH₂ shuttle high-energy electrons to the electron transport chain for efficient energy extraction.
  • Stepwise Energy Release: Prevents loss as heat and maximizes ATP yield.

Regulation of Cellular Respiration

  • Phosphofructokinase (PFK): A key allosteric enzyme controlling glycolysis. ATP and citrate inhibit PFK, while AMP stimulates it, allowing cells to adjust respiration to energy demands.

Key Terms and Glossary

  • ATP (Adenosine Triphosphate): Main cellular energy carrier.
  • Glycolysis: Breakdown of glucose to pyruvate, producing ATP and NADH.
  • Citric Acid Cycle (Krebs Cycle): Series of reactions producing ATP, NADH, and FADH₂ from acetyl CoA.
  • Oxidative Phosphorylation: ATP synthesis via electron transport and chemiosmosis.
  • Electron Transport Chain (ETC): Proteins transferring electrons to create a proton gradient.
  • Chemiosmosis: Using a proton gradient to drive ATP synthesis.
  • Fermentation: ATP production in absence of oxygen.
  • Redox Reaction: Chemical reaction involving electron transfer.
  • NADH/FADH₂: Electron carriers in respiration.
  • Phosphofructokinase (PFK): Allosteric enzyme regulating glycolysis.

Conclusion: Energy Production at the Cellular Level

Chapter 9 of Campbell Biology gives a comprehensive look at how cells generate and regulate energy. Mastering these concepts is crucial for understanding cell physiology, energy balance, and the biochemical basis of life. For a detailed walkthrough, watch our full video summary and explore more biology chapter guides from Last Minute Lecture.

If this summary helped you grasp cellular respiration and fermentation, be sure to watch the video above and subscribe to our channel for ongoing science support and new content every week.

If you found this breakdown helpful, be sure to subscribe to Last Minute Lecture for more chapter-by-chapter textbook summaries and academic study guides.

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