Cellular Respiration Overview

Overview

This lecture explains aerobic cellular respiration in eukaryotic cells, detailing the steps involved in ATP production and the critical role of mitochondria.

ATP and Its Importance

• ATP (adenosine triphosphate) is the main energy currency of cells.
• All cells, prokaryotic and eukaryotic, need ATP for vital processes.
• ATP is a nucleic acid with three phosphates, providing energy when a phosphate bond is broken.

Overview of Aerobic Cellular Respiration

• Aerobic cellular respiration is the process cells use to generate ATP using oxygen.
• Eukaryotic cells, with membrane-bound organelles like mitochondria, perform this process.
• The main goal of respiration is to break down glucose and produce ATP.

Aerobic Cellular Respiration Equation

• Reactants (inputs): glucose and oxygen.
• Products (outputs): carbon dioxide, water, and ATP.
• Photosynthesis and respiration are related but not opposites; plants do both, others rely on consuming glucose.

Steps of Aerobic Cellular Respiration

Step 1: Glycolysis

• Occurs in the cytoplasm and does not require oxygen (anaerobic).
• Glucose is converted into 2 pyruvate, yielding a net 2 ATP and 2 NADH.
• NADH is a coenzyme that transfers electrons for further ATP production.

Intermediate Step: Pyruvate Oxidation

• Pyruvate enters the mitochondrial matrix and is converted to 2 acetyl CoA.
• 2 NADH are produced and CO₂ is released during this step.

Step 2: Krebs (Citric Acid) Cycle

• Takes place in the mitochondrial matrix and is aerobic.
• Each glucose yields 2 ATP, 6 NADH, 2 FADH₂, and releases CO₂.
• FADH₂ is also a coenzyme for electron transfer.

Step 3: Electron Transport Chain and Chemiosmosis

• Occurs in the inner mitochondrial membrane and requires oxygen.
• Electrons from NADH and FADH₂ are used to create a proton gradient.
• Protons move through ATP synthase, powering the formation of ATP from ADP.
• Oxygen serves as the final electron acceptor, forming water.

ATP Yield and Efficiency

• Electron transport chain and chemiosmosis generate about 26-34 ATP per glucose.
• Total ATP yield from one glucose: approximately 30-38 ATP (varies with conditions).

Alternate Pathways and Cellular Health

• If oxygen is absent, cells may switch to fermentation (less efficient ATP production).
• Mitochondria are essential for ATP production; inhibitors like cyanide can be fatal.
• Ongoing research targets mitochondrial diseases due to their crucial role in energy production.

Key Terms & Definitions

• ATP (Adenosine Triphosphate) — main energy molecule used by cells.
• Glycolysis — first step where glucose is broken down in cytoplasm.
• NADH/FADH₂ — coenzymes that transfer electrons during respiration.
• Krebs/Citric Acid Cycle — mitochondrial cycle producing electron carriers and ATP.
• Electron Transport Chain — series of proteins in mitochondria that produce most ATP.
• Chemiosmosis — movement of protons driving ATP synthesis via ATP synthase.
• Fermentation — anaerobic process for ATP production when oxygen is absent.

Action Items / Next Steps

• Review detailed steps of the Citric Acid Cycle in suggested readings.
• Watch related videos on ATP and fermentation for deeper understanding.