Cellular Respiration Overview

Overview

• Cellular respiration is the process cells use to obtain energy from glucose.
• Glucose is broken down into carbon dioxide and water, releasing energy stored as ATP.
• It's essential for all living organisms and is an aerobic process, requiring oxygen.
• The overall equation is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP.
• Involves four main stages: glycolysis, pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation.

Stages of Cellular Respiration

• Glycolysis: First stage, anaerobic, in the cytoplasm.

  • Breaks down glucose (6 carbons) into two pyruvate molecules (3 carbons each) in a 10-step enzymatic process.
  • Produces a net gain of 2 ATP molecules and 2 NADH electron carriers per glucose molecule.
  • Important even in anaerobic respiration (fermentation).
  • Has two phases: energy investment phase (using 2 ATP) and energy payoff phase (producing 4 ATP and 2 NADH). Net gain is 2 ATP, 2 NADH, and 2 pyruvate molecules.

• Pyruvate Oxidation: Transition step between glycolysis and the Krebs cycle. In the mitochondrial matrix.

  • Converts pyruvate to acetyl CoA (a 2-carbon molecule).
  • Releases carbon dioxide as a byproduct.
  • Produces 1 NADH per pyruvate molecule (2 NADH per glucose).

• Krebs Cycle (Citric Acid Cycle): In the mitochondrial matrix.

  • Acetyl CoA combines with oxaloacetate to form citrate.
  • Series of oxidation-reduction reactions release CO₂, transfer electrons to electron carriers (NAD⁺ and FAD), creating NADH and FADH₂.
  • Produces 1 ATP, 3 NADH, and 1 FADH₂ per acetyl CoA. Per glucose molecule, net production of: 2 ATP, 6 NADH, and 2 FADH₂.

• Oxidative Phosphorylation: In the inner mitochondrial membrane.

  • Most ATP is generated here.
  • NADH and FADH₂ donate electrons to the electron transport chain, releasing energy to pump protons (H⁺) across the membrane, creating a gradient.
  • Protons flow back through ATP synthase, driving ATP synthesis from ADP and inorganic phosphate.
  • Oxygen is the final electron acceptor, forming water.
  • High ATP yield: 32-34 ATP per glucose molecule.

Types of Cellular Respiration

• Aerobic respiration: Requires oxygen, generates significantly more ATP than anaerobic.
• Anaerobic respiration (fermentation): Does not require oxygen, produces much less ATP, uses alternative electron acceptors. Both are vital metabolic pathways with importance in different environments or situations.

ATP Production Summary

• Cellular respiration is highly efficient in generating ATP.
• Aerobic respiration yields significantly more ATP than anaerobic respiration.

Regulation of Cellular Respiration

• Cellular respiration rate adjusts according to cellular energy needs.
• Feedback mechanisms and hormones control the rate of enzyme activity in the various stages.

Importance of Cellular Respiration

• Provides energy for cell functions (muscle contraction, protein synthesis, active transport).
• Essential for maintaining homeostasis and crucial for the survival of all living organisms..