Steps of Cellular Respiration

Introduction

• Cellular respiration is a metabolic pathway that converts glucose into ATP.
• Consists of four main stages: Glycolysis, Pyruvate Oxidation, Citric Acid Cycle (Krebs Cycle), and Oxidative Phosphorylation.

Overview of Cellular Respiration

• Glucose is broken down into carbon dioxide and water.
• Direct ATP production during reactions transforming glucose.
• Major ATP production occurs during oxidative phosphorylation via the electron transport chain.
• Electron carriers (NAD+ and FAD) shuttle electrons to the electron transport chain.

Detailed Steps of Cellular Respiration

1. Glycolysis

   • Occurs in the cytosol.
   • Six-carbon glucose converted into two three-carbon pyruvates.
   • Produces ATP and converts NAD+ to NADH.

2. Pyruvate Oxidation

   • Occurs in the mitochondrial matrix.
   • Each pyruvate is transformed into acetyl CoA (two-carbon molecule).
   • Releases CO2 and generates NADH.

3. Citric Acid Cycle (Krebs Cycle)

   • Acetyl CoA combines with a four-carbon molecule.
   • Cycle regenerates the starting four-carbon molecule.
   • Produces ATP (or GTP), NADH, FADH2, and releases CO2.

4. Oxidative Phosphorylation

   • NADH and FADH2 deposit electrons into the electron transport chain (inner mitochondrial membrane).
   • Electron movement releases energy to pump protons, creating a gradient.
   • Protons flow back via ATP synthase, producing ATP.
   • Oxygen accepts electrons and protons, forming water.

Anaerobic Conditions

• Fermentation: Glycolysis can occur without oxygen, leading to fermentation.
• Pyruvate oxidation, citric acid cycle, and oxidative phosphorylation require oxygen.

Additional Notes

• Cellular respiration stages are detailed in further articles and videos on Khan Academy.
• Different terminologies can describe similar processes (e.g., Krebs Cycle is also the Citric Acid Cycle).

Prokaryotes and Cellular Respiration

• Prokaryotes perform cellular respiration differently due to the absence of mitochondria.
• Glycolysis occurs in the cytoplasm; citric acid cycle in the cytoplasm, and electron transport chain in the plasma membrane.

Key Concepts

• Cellular respiration is a stepwise, controlled process for efficient energy extraction.
• Energy, intermediates, and electron carriers (ATP, NADH, FADH2) are critical outputs at various stages.

Reference

• Refer to the Khan Academy for further explanations and visuals.

This summary captures the essence of cellular respiration's steps as explained in the Khan Academy article.