CELLULAR RESPIRATION

• Cellular Respiration

  The step-wise process that releases energy by breaking down food molecules in the presence of oxygen
• Cellular Respiration

  Oxygen + Glucose Carbon Dioxide + Water + Energy
• Carbohydrates, fats and proteins can all be used to make energy in the form of ATP via cellular respiration
• Anaerobic Respiration

  1. Glycolysis

  2. Fermentation
• Glycolysis

  The breakdown of glucose to two molecules of pyruvate in the cytoplasm. No oxygen is required. Yields 2 ATP. Glycolysis occurs in ALL organisms.
• Fermentation

  If oxygen is not present, pyruvate is metabolized into pyruvic acid. Fermentation makes it possible for ATP to be continually produced if oxygen is unavailable.
• If oxygen is unavailable

  Fermentation occurs
• Anaerobic Respiration

  In animals the by-product is lactic acid, in plants the by-product is ethanol.
• If oxygen is present

  Pyruvate enters the mitochondria and AEROBIC respiration occurs
• Aerobic Respiration

  1. Allows pyruvate (from glycolysis) to combine with oxygen and enter the mitochondria.

  2. A series of reactions occurs to completely breakdown (or combust) the glucose:

  3. glycolysis

  4. Kreb Cycle

  5. Electron Transport Chain

  6. This yields a further 36 ATP molecules
• Krebs Cycle

  1. The Krebs cycle (or Citric Acid Cycle) occurs in the mitochondrial matrix.

  2. Is a cyclical series of oxidation reactions that:

  3. Release carbon dioxide

  4. Produce one ATP, NADH, FADH

  5. Occurs twice per glucose molecule
• Electron Transport Chain

  1. The electron transport chain (ETC), is a series of carriers that accept electrons removed from glucose, passing them from one carrier to the next until the final receptor.

  2. Oxygen is required

  3. Water is produced

  4. Energy is released and used to synthesise 34 to 36 ATP
• Accounting of energy yield per glucose molecule breakdown

  • Fermentation (Anaerobic Respiration):
  • ADVANTAGES: Can provide a rapid burst of ATP in muscle cells when oxygen is in limited supply. Produces 2 ATP equivalent to 61 kJ per molecule of glucose
  • DISADVANTAGES: Lactic acid is produced (at first is carried away by blood – but eventually builds up affecting cell capacity to produce ATP). Oxygen debt occurs and liver must convert lactate to pyruvate. Complete oxidation of glucose makes 2870 kJ of energy (fermentation has around 2.1% the efficiency of aerobic cellular respiration)
• Each molecule of glucose can generate *36-38 molecules of ATP in aerobic respiration but only 2 ATP molecules in respiration without oxygen (through glycolysis and fermentation).
• Aerobic Respiration

  • Uses oxygen
  • In most cells (i.e. eukaryotes)
  • No production of Lactic Acid
  • High amount of energy released - 36 to 38 ATP
  • Reactants: glucose, oxygen
  • Products: carbon dioxide, water, ATP
  • Site of reaction: cytosol and mitochondria
  • Stages: Glycolysis, Kreb Cycle, Electron Transport Chain
  • Complete breakdown of glucose (combustion)
• Anaerobic Respiration

  • Occurs without oxygen
  • In Bacteria, Yeast, Red blood cells and muscle cells
  • Produces Lactic Acid (in animals) or Ethanol (in plants)
  • Low amount of energy released - 2 ATP
  • Reactants: glucose
  • Products: Lactic acid, ATP OR ethyl alcohol, carbon dioxide, ATP
  • Site of reaction: cytosol
  • Stages: Glycolysis (fermentation)
  • Incomplete breakdown of glucose
• ATP

  Adenosine Triphosphate - delivers energy to, or picks up energy from almost all metabolic pathways. ATP is a ready donor of energy. There is an ATP/ADP cycle, where a phosphate molecule is added to ADP to form ATP. Cellular respiration creates the pathway for this process to occur. The energy is contained in the bond that is released when ATP loses a phosphate and becomes ADP.
• The energy released (when ATP is broken down to ADP) is used by cells for: Growth in terms of breaking down molecules and synthesising new ones, Cell division (mitosis), Movement (muscles/transport of materials), Active transport, Maintenance of body temperature
• Why ATP is a great energy source

  • It can be recycled (ATP<->ADP+P) by cellular respiration.
  • When energy is needed, only one bond has to be broken (breaking down of glucose has many steps).
  • Is easily used by proteins (including enzymes)
  • Alternatives may not provide as much energy
  • Alternatives can be toxic
  • Is a relatively small energy molecule.
• Comparison: Photosynthesis and Respiration

  • Photosynthesis:
  • Function: Energy Storage (glucose)
  • Location: Chloroplasts
  • Reactants: CO2 and H2O
  • Products: C6H12O6 and O2
  • Equation: 6CO2 + 6H2O C6H12O6 + 6O2
  • Respiration:
  • Function: Energy Release (ATP)
  • Location: Mitochondria
  • Reactants: C6H12O6 and O2
  • Products: CO2 and H2O
  • Equation: C6H12O6 + 6O2 6CO2 + 6H2O
• Photosynthesis and Aerobic Respiration are Complimentary. The inputs of one are the outputs of the other and vice versa. Energy in carbon-carbon bonds drive life. Energy changes from one form to another throughout this cycle: light energy chemical energy (sometimes electrical energy) heat energy
• Compensation Point

  When the rate of production of glucose and oxygen by photosynthesis equals the consumption of glucose and oxygen in cellular respiration, then the compensation point is reached.