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Cellular Respiration: Converting Food into Energy for Life

Cellular respiration is the biochemical process that converts glucose into ATP, the energy currency of cells, utilizing chemical energy from food. This metabolic pathway occurs in both plants and animals, starting with glycolysis, which breaks down glucose into pyruvate. Subsequent reactions include the Krebs cycle and the electron transport chain, the latter producing the majority of ATP. Anaerobic respiration, such as fermentation, allows organisms to generate energy without oxygen, resulting in products like ethanol and lactic acid. This process is crucial for energy production and metabolic function in various environments.

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Cellular Respiration: Converting Food into Energy for Life

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  1. Chapter 9: Cellular Respiration

  2. Chemical Energy and Food • A calorie is the energy required to raise 1g of water 1˚C • 1g of glucose releases 3811 calories • 1 Calorie (capital “C”) on food labels is actually a kilocalorie (1000 calories) • 1g of glucose releases 3.811 Calories

  3. Using Chemical Energy • Plants and animals both use glucose for metabolic fuel • Glucose is not directly usable • Must be converted into ATP first

  4. Cellular Respiration Overview • Converts glucose into ATP • Occurs in both plants and animals • Cellular Respiration Reaction: • C6H12O6 + 6O2→ 6CO2 + 6H2O • Opposite of photosynthesis -6CO2 + 6H2O → C6H12O6 + 6O2

  5. Glycolysis • Series of reactions which break a 6-carbon glucose molecule into two 3-carbon molecules called pyruvic acid (a.k.a. pyruvate) • Occurs in the cytoplasm Glucose 2 Pyruvate 2 G3P to electron transport chain

  6. Glycolysis • Process is ancient • all organisms from simple bacteria to humans perform it the same way • Yields2 ATPand2 NADHper glucose molecule Glucose 2 Pyruvate 2 G3P to electron transport chain

  7. Glycolysis Overview: • Glucose is converted into 2 pyruvic acid molecules • A.K.A. pyruvate • Pyruvic acid is a reactant in the Krebs Cycle

  8. Glycolysis Step 1: • The cell invests 2 ATP to convert glucose  2 G3P

  9. Glycolysis Step 2: • 4 ATP molecules are produced from the conversion of 2 G3P 2 pyruvic acid • 2 NADH molecules are produced • Used in E.T.C.

  10. Glycolysis

  11. Aerobic Cellular Respiration • Oxygen required = aerobic • 2 more sets of reactions which occur in a specialized organelles called mitochondria 1. The Krebs Cycle 2. The Electron Transport Chain

  12. The Krebs Cycle • AKA The Citric Acid Cycle • Completes the breakdown of glucose • Carbon and oxygen atoms end up in CO2 and H2O, respectively • Produces only 2 more ATP • but produces electron carriers NADH and FADH2 which move to the 3rd stage (The Electron Transport Chain)

  13. The Krebs Cycle Citric Acid Production

  14. The Krebs Cycle Products (per glucose): • 6 CO2 • 2 ATP • 8 NADH • 2 FADH2 to E.T.C.

  15. Electron Transport Chain • Powered by electron carriers from the Kreb’s Cycle • Produces a total of 32 ATP • Water is formed when oxygen combines with protons

  16. The Electron Transport Chain Hydrogen Ion Movement Electron Transport H+ Active Transport H+ Diffusion Intermembrane Space ATP synthase Inner Membrane Mitochondrial Matrix ATP Production

  17. Energy Tally • 36 ATP for aerobic vs. 2 ATP for anaerobic • Glycolysis 2 ATP • Krebs 2 ATP • Electron Transport Chain 32 ATP 36 ATP • Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

  18. Anaerobic Cellular Respiration • Also called fermentation • Some organisms thrive in environments with little or no oxygen • Marshes, bogs, digestive tracts, sewage treatment tanks, etc. • No oxygen used = anaerobic • Results in no more ATP • The final steps in these pathways serve ONLY to regenerate NAD+ so it can keep glycolysis running • End products such as ethanol and CO2 (yeast in beer/bread) or lactic acid (muscle cells)

  19. Fermentation Overview

  20. Alcoholic Fermentation • Used by yeasts and other microorganisms • Produces carbon dioxide and ethanol • Used to make bread and alcoholic drinks (beer, wine, etc.)

  21. Lactic Acid Fermentation • Used by both unicellular and multicellular organisms • Lactic acid buildup in muscles causes a burning sensation • Used in the production of sour cream, cheese, yogurt, and many other foods & beverages Glucose Pyruvic Acid Lactic Acid

  22. Fermentation Overview

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