Cellular Respiration Overview

Overview

This lecture explains aerobic cellular respiration in eukaryotic cells, focusing on how ATP is produced through a multi-step process primarily within the mitochondria.

ATP and Cellular Respiration

• ATP (adenosine triphosphate) is the primary energy currency of the cell.
• All cells (prokaryotic and eukaryotic) require ATP for survival and active processes.
• Eukaryotic cells perform aerobic cellular respiration, mainly in mitochondria, to make ATP.

Aerobic Cellular Respiration Overview

• The main goal is to break down glucose to make ATP.
• The overall equation for aerobic respiration has reactants (inputs): glucose and oxygen; products (outputs): carbon dioxide, water, and ATP.
• Plants perform both photosynthesis (making glucose) and cellular respiration (breaking down glucose); animals and non-photosynthetic organisms must obtain glucose from food.

Step 1: Glycolysis

• Occurs in the cytoplasm and is anaerobic (does not require oxygen).
• Glucose is converted into 2 pyruvate, with a net gain of 2 ATP and 2 NADH.
• NADH acts as an electron carrier for later steps.

Intermediate Step: Pyruvate Oxidation

• Pyruvate is transported into the mitochondrial matrix and oxidized.
• 2 pyruvate become 2 acetyl CoA, releasing CO₂ and producing 2 NADH.

Step 2: Krebs Cycle (Citric Acid Cycle)

• Takes place in the mitochondrial matrix and is considered aerobic.
• 2 acetyl CoA enter the cycle; products are 2 ATP, 6 NADH, 2 FADH₂, and CO₂.
• FADH₂, like NADH, will transfer electrons in the next step.

Step 3: Electron Transport Chain and Chemiosmosis

• Located in the inner mitochondrial membrane; requires oxygen.
• NADH and FADH₂ donate electrons to create a proton gradient.
• Protons flow through ATP synthase, powering ATP production from ADP.
• Oxygen is the final electron acceptor, forming water.
• This step produces the most ATP, with estimates ranging from 26–34 ATP per glucose.

ATP Yield

• Total ATP yield from aerobic respiration per glucose molecule is roughly 30–38, depending on various factors.

Alternate Pathways and Importance

• In absence of oxygen, cells can use fermentation, which is less efficient.
• Disruption of cellular respiration (e.g., by cyanide) can be deadly.
• Mitochondrial diseases highlight the importance of ATP production research.

Key Terms & Definitions

• ATP (Adenosine Triphosphate) — primary energy carrier in cells.
• Glycolysis — first step of respiration; splits glucose in the cytoplasm.
• Pyruvate — end product of glycolysis, entering the mitochondria.
• NADH/FADH₂ — coenzymes that transfer electrons for ATP production.
• Acetyl CoA — compound entering the Krebs cycle.
• Krebs Cycle (Citric Acid Cycle) — a series of reactions generating high-energy carriers.
• Electron Transport Chain — sequence of proteins that transfer electrons to make ATP.
• Chemiosmosis — use of a proton gradient to drive ATP synthesis.
• ATP Synthase — enzyme that synthesizes ATP in mitochondria.
• Fermentation — alternative pathway to produce ATP without oxygen.

Action Items / Next Steps

• Review further readings on the Krebs Cycle as suggested.
• Watch additional videos on ATP, fermentation, and cell transport for deeper understanding.