lecture recording on 10 February 2025 at 12.36.48 PM

Cellular Respiration Overview

• Cellular respiration converts energy from glucose into usable forms such as ATP, involving multiple steps and reactions.

Glycolysis

• Occurs in the cytoplasm.

• Converts 1 glucose molecule into 2 pyruvate molecules.

• Energy changes: yields 2 NADH (no CO2 production).

• Total energy produced: 2 ATP.

• Important molecules produced: pyruvate.

Transition Reaction

• Location: moves from cytosol to mitochondrial matrix.

• Converts pyruvate into acetyl CoA.

• Generates 2 NADH from 1 glucose.

Citric Acid Cycle (Krebs Cycle)

• Takes place in the mitochondrial matrix.

• Uses acetyl CoA to generate various products:

  • Citrate is formed and subsequently converted to isocitrate, releasing carbon dioxide and generating NADH.

  • Further transformations include:

    • Alpha-ketoglutarate to succinyl CoA, another CO2 release and another NADH.

    • Succinyl CoA to succinate, producing GTP/ATP.

    • Fumarate to succinate produces FADH2.

    • Malate to oxaloacetate produces another NADH, regenerating oxaloacetate to continue the cycle.

• Total outputs for one glucose:

  • 6 NADH

  • 2 FADH2

  • 2 ATP

  • 4 CO2

• Key molecule produced: oxaloacetate.

Importance of Oxygen

• Oxygen is not directly required during glycolysis and the Krebs cycle, but is crucial for the electron transport chain where it serves as the final electron acceptor.

The Role of Decomposers

• Decomposers (bacteria and fungi) play a vital role in the carbon cycle by converting organic matter in dead bodies into CO2.

• Carbon Cycle: Carbon from dead organisms is turned into CO2, which plants absorb and utilize for photosynthesis.

Cell Metabolism

• Metabolic processes convert glucose into various biomolecules:

  • Nucleotides for DNA.

  • Lipids for membranes.

  • Amino acids for proteins.

Energy Source for Organisms

• The original energy source for most organic compounds in organisms is sunlight captured by photosynthesis in plants.

• Fundamental equation: Photosynthesis generates glucose and oxygen from CO2 and water with sunlight, while cellular respiration breaks down glucose for energy, producing CO2 and H2O.

Exam Question Review

• When a living organism exhales CO2 after inhaling O2, the mass decreases because it releases heavier carbon atoms compared to the lighter oxygen molecules inhaled.

• Organic matter is not directly absorbed from the soil but decomposed into CO2 by fungi and bacteria, making it available for plants.

Applications in Ecosystems

• Understanding the carbon cycle is crucial for tracing carbon movement from organic matter (e.g., a deceased organism) through consumers in an ecosystem.

• Carbon atoms transfer from dead organisms to plants, consumers, and repeated through the food web, showcasing the interconnectedness of life and energy flow in ecosystems.

Additional Insights

• Not all organisms derive carbon from glucose; examples include certain bacteria in extreme environments that use alternative energy sources (iron sulfur clusters or acetic acid).

Summary of Cellular Processes

• Photosynthesis vs. Cellular Respiration:

  • Photosynthesis: CO2 + H2O + light energy -> glucose + O2.

  • Cellular Respiration: glucose + O2 -> CO2 + H2O + ATP.

• Plants perform both processes, but animals primarily carry out cellular respiration.