Understanding Cell Respiration Processes

Oct 30, 2024

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Lecture Notes: Cell Respiration

Introduction

  • Cell respiration involves the breakdown of food into ATP, the cell's energy currency.
  • Common misconception: cell respiration is not limited to glucose.
  • Focus for this lecture: glucose metabolism.

Overview of Cell Respiration Steps

  1. Glycolysis
  2. Link Reaction
  3. Krebs Cycle
  4. Electron Transport Chain & Chemiosmosis
    • Requires oxygen (aerobic respiration).
    • Anaerobic respiration occurs when oxygen is absent.

Oxidation and Reduction (Redox Reactions)

  • Oxidation: loss of electrons and hydrogens.
  • Reduction: gain of electrons and hydrogens.
  • "Oil Rig" mnemonic: Oxidation is loss, Reduction is gain.
  • Redox reactions are crucial throughout cell respiration.

Glycolysis

  • Location: Cytoplasm.
  • Glycolysis = splitting of glucose.
  • Steps:
    1. Phosphorylation: Glucose reacts with ATP; ATP donates phosphates to glucose (phosphorylation).
    2. Lysis: Glucose splits into two triose phosphates.
    3. Oxidation and Reduction: Triose phosphates oxidized; NAD+ reduced to NADH.
    4. ATP Formation: Phosphates transferred to ADP, forming ATP.
  • Products: 2 ATP (net), 2 NADH, 2 Pyruvate.

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Link Reaction

  • Occurs in the mitochondrial matrix.
  • Pyruvate transported into mitochondria.
  • Decarboxylation: Pyruvate loses CO2 to form acetyl group.
  • NAD+ reduced to NADH.
  • Coenzyme A binds with acetyl group to form Acetyl-CoA.
  • Products (per glucose): 2 NADH, 2 CO2, 2 Acetyl-CoA.

Krebs Cycle (Citric Acid Cycle)

  • Location: Mitochondrial matrix.
  • Acetyl-CoA combines with oxaloacetate to form citrate.
  • Steps involve decarboxylation and multiple redox reactions.
  • Products per cycle: 3 NADH, 1 FADH2, 1 ATP, 2 CO2.
  • Since each glucose produces 2 acetyl-CoA, total products: 6 NADH, 2 FADH2, 2 ATP, 4 CO2.

Electron Transport Chain (ETC) & Chemiosmosis

  • Location: Inner mitochondrial membrane.
  • NADH and FADH2 donate electrons to the ETC.
  • Electrons passed through carriers, driving H+ (proton) pumping into the intermembrane space.
  • Proton gradient drives ATP synthesis via ATP synthase (chemiosmosis).
  • Oxygen acts as the final electron acceptor, forming water.
  • Total ATP yield from oxidative phosphorylation: ~32 ATP.

Anaerobic Respiration

  • Occurs when oxygen is absent.
  • Glycolysis still proceeds, producing 2 ATP.
  • In animals: pyruvate converted to lactate (lactic acid fermentation).
  • In yeast: pyruvate converted to ethanol and CO2 (alcohol fermentation).
  • Regenerates NAD+ for glycolysis.

Alternative Respiratory Substrates

  • Besides glucose, lipids and amino acids can also be used.
  • Lipids: Broken into acetyl-CoA, entering Krebs Cycle.
  • Amino acids: Enter Krebs Cycle at various points.
  • Lipids provide more ATP than glucose per gram.

Key Takeaways

  • NADH and FADH2 are critical for ATP production in ETC.
  • Oxygen is essential as the final electron acceptor for aerobic respiration.
  • Understanding the roles of different molecules in each step is crucial for mastering cell respiration.

Quiz Questions

  1. Which stage yields the most ATP?
    • Answer: Oxidative Phosphorylation.
  2. What is formed when glucose undergoes glycolysis?
    • Answer: 2 ATP, 2 NADH, 2 Pyruvate.
  3. What is the final electron acceptor in aerobic respiration?
    • Answer: Oxygen.

This lecture provides comprehensive detail on the processes of cell respiration, emphasizing the need to understand the stages and the role of molecules involved.