Cellular Respiration Overview

Overview

This lecture explains aerobic cellular respiration in eukaryotic cells, focusing on how ATP (the cell's energy currency) is produced through three main steps.

Importance of ATP and Cellular Respiration

• ATP (adenosine triphosphate) is the energy currency for cells, necessary for active transport and other cell processes.
• All cells—prokaryotic and eukaryotic—must produce ATP to survive.
• Eukaryotic cells, including plants, animals, fungi, and protists, perform aerobic cellular respiration mainly in the mitochondria.

Overview of Aerobic Cellular Respiration

• The main goal of aerobic respiration is to convert glucose into ATP.
• The general equation shows glucose and oxygen as inputs; carbon dioxide, water, and ATP as outputs.
• Cellular respiration is not simply the opposite of photosynthesis, but shares some substances.

Step 1: Glycolysis

• Glycolysis occurs in the cytoplasm and does not require oxygen (anaerobic).
• Glucose is converted to 2 pyruvate, yielding 2 ATP (net) and 2 NADH.
• NADH is a coenzyme, helping transfer electrons for later ATP production.

Intermediate Step: Formation of Acetyl CoA

• Pyruvate is actively transported into the mitochondrial matrix and converted to acetyl CoA.
• 2 NADH and CO₂ are produced in this step.

Step 2: Krebs Cycle (Citric Acid Cycle)

• Occurs in the mitochondrial matrix and is considered aerobic (requires oxygen indirectly).
• Each turn releases CO₂, and produces 2 ATP, 6 NADH, and 2 FADH₂.
• FADH₂ is another electron-transferring coenzyme.

Step 3: Electron Transport Chain and Chemiosmosis

• Takes place along the inner mitochondrial membrane; requires oxygen.
• Electrons from NADH and FADH₂ move through proteins, creating a proton gradient.
• ATP synthase uses the gradient to convert ADP into ATP.
• Oxygen acts as the final electron acceptor, making water as a product.
• This step produces the majority of ATP (about 26-34 ATP per glucose); total net yield per glucose is 30-38 ATP.

Alternative Pathway: Fermentation

• In the absence of oxygen, some cells perform fermentation, which makes less ATP than aerobic respiration.

Cellular Respiration and Health

• Poisons like cyanide can block the electron transport chain, preventing ATP production and causing cell death.
• Research into mitochondrial diseases is ongoing due to mitochondria's critical role in energy production.

Key Terms & Definitions

• ATP (Adenosine Triphosphate) — main energy carrier in the cell.
• Glycolysis — first step breaking down glucose to pyruvate in the cytoplasm.
• NADH/FADH₂ — coenzymes carrying electrons to the electron transport chain.
• Krebs Cycle (Citric Acid Cycle) — cycle in mitochondria producing electron carriers and some ATP.
• Electron Transport Chain — series of proteins in mitochondria making most ATP during respiration.
• Chemiosmosis — process using a proton gradient to drive ATP synthesis.
• Fermentation — ATP-producing process used when oxygen is not available.

Action Items / Next Steps

• Review the equation for aerobic cellular respiration and identify reactants and products.
• Read more about the Krebs Cycle as suggested in further reading materials.
• Watch the referenced videos on ATP and fermentation for deeper understanding.