Cellular Respiration

Overview of Cellular Respiration

• Cellular respiration is a biochemical process that occurs at the cellular level.

• Confusion often arises between respiration (breathing) and cellular respiration; the latter occurs inside mitochondria and requires oxygen.

• It involves breaking down food to produce ATP, the energy currency of the cell.

Respiration in Different Organisms

• Bacteria do not require mitochondria to perform respiration; they can use their outer membranes for aerobic respiration.

• Example: Track athletes (like Usain Bolt) utilize respiration for energy to power their muscular movements.

Energy Output and Physical Performance

• A study was conducted to analyze world records in running events (100m to 10,000m) to determine running paces.

  • Data showed a sharp pace decline during sprints, stabilizing over longer distances.

• Discussion on aerobic vs anaerobic respiration.

  • Aerobic respiration: requires oxygen, more efficient for longer activities.

  • Anaerobic respiration: provides quick energy bursts, leading to lactic acid build-up during high-intensity activities like the 400m sprint.

Muscle Fatigue Experiment

• Conducted a lab where students repeatedly squeezed a tennis ball.

  • Performance declined over time as energy shifted from aerobic to anaerobic pathways due to lactic acid accumulation.

Purpose of Cellular Respiration

• Cellular respiration is essential for heterotrophs (organisms that obtain organic compounds for energy).

• Heterotrophs (animals, fungi, bacteria) convert organic materials into carbon dioxide, water, and ATP.

• Autotrophs (plants, algae) convert CO2 and water back into organic material, thus participating in both photosynthesis and cellular respiration.

Chemical Equation of Cellular Respiration

• The process can be summarized with the equation: [ C_6H_{12}O_6 + O_2 \rightarrow CO_2 + H_2O + ATP \ ]

• Glucose is broken down in the presence of oxygen, releasing energy stored in hydrogen atoms.

Mitochondrial Structure and Function

• Mitochondria have unique structures crucial for respiration:

  • Cristae: folds on the inner mitochondrial membrane increase surface area for reactions.

  • Inner and outer membranes create distinct spaces crucial for different stages of respiration.

  • Mitochondria are thought to have originated from symbiotic bacteria; they contain their own DNA and replicate independently.

Stages of Cellular Respiration

• 1. Glycolysis

  • Occurs in the cytoplasm; glucose (six-carbon molecule) is converted into two pyruvate molecules (three-carbon each).

  • Produces 2 ATP and NADH (which carries high-energy electrons).

• 2. Krebs Cycle (Citric Acid Cycle)

  • Pyruvate enters the mitochondria and is converted into acetyl CoA, releasing CO2.

  • The Krebs Cycle produces 2 ATP and generates NADH and FADH2, which carry electrons to the next step.

• 3. Electron Transport Chain (ETC)

  • Takes place in the inner mitochondrial membrane; most ATP is generated here (32-34 ATP).

  • NADH and FADH2 donate electrons to a series of proteins, pumping protons into the intermembrane space.

  • Oxygen acts as the final electron acceptor, combining with electrons and protons to form water.

Anaerobic Respiration and Fermentation

• In the absence of oxygen, organisms undergo lactic acid fermentation to recycle NAD+ and allow glycolysis to continue.

  • Results in lactic acid buildup in muscles, causing fatigue.

  • Example: Sprinters experience lactic acid buildup, making it difficult to maintain performance without breathing.

• Alcoholic fermentation is another anaerobic process (common in yeast); breaks glucose into ethanol and CO2, useful in making alcohol products.

Conclusion

• Cellular respiration is crucial for energy extraction from various food sources.

• It demonstrates the biochemical interconnectedness of all life forms (bacteria, plants, animals).