Cellular respiration

• Cellular Respiration

  • Process by which organic molecules, (food) are broken down in the cells to release energy (ATP) for the cell’s activities
  • Can release energy from glucose amino acids fatty acids and glycerol
• Organic compounds


  • Molecules with a carbon chain
  • Contain a hydrogen atom
  • May include atoms of oxygen, nitrogen and sulfur
• Organic compounds


  • carbohydrates
  • lipids
  • proteins
• Carbohydrates


  • Main source of energy
  • Simple sugars e.g. glucose
  • Made of carbon, hydrogen and oxygen
• Lipids


  • Fats and oil
  • Broken down into fatty acids and glycerol
  • Glycerol can enter glycolysis pathway of cellular respiration
  • Each lipid molecule consists of one molecule of glycerol and 1-3 fatty acid molecules
• Proteins


  • Made of many amino acids
  • Enzymes most important proteins for metabolism
  • Can be used as source of energy but only if carbohydrates and lipids are not available
• Inorganic compounds


  Not based on a carbon chain
• Inorganic compounds


  • water
  • minerals
  • vitamins
• Importance of inorganic compounds for metabolism

  • Water: fluid in which substances are dissolved, some cell's chemical reactions occur in water
  • Minerals: may be part of enzymes, may function as cofactors, may be part of ATP
  • Vitamins: coenzymes for many chemical reactions of metabolism
• Energy from cellular respiration:

  • ATP is formed when a phosphate is joined to an adenosine diphosphate or ADP
  • Energy is held between the 2nd and 3rd phosphate
  • When the high energy chemical bond between the ADP and third phosphate group is broken – energy is released and used within the cell
  • ADP can then be reused to store energy later from cellular respiration, transferring energy  to where it is required in the cell
• Glycolysis:

  • First phase in the breakdown of glucose
  • No oxygen required
  • 1 glucose molecule broken down into 2 pyruvate molecules
  • Results in production of 2 ATP
• Oxygen Availability:

  • Depends on if oxygen is available or not available
  • No oxygen = anaerobic respiration
  • Important during vigorous physical activity
  • Oxygen = aerobic respiration
• Anaerobic Reaction:

  • When no oxygen is available
  • Pyruvate converted to lactic acid by fermentation
  • No ATP produced – but still have 2 ATP produced from glycolysis
  • Occurs in cytosol
  • Important during vigorous activity – when unable to supply enough oxygen to meet energy demands
  • Accumulation of lactic acid in muscles causes pain
• Anaerobic reaction oxygen debt:

  • Lactic acid taken to liver via blood
  • Recombines with oxygen to form glucose then glycogen
  • This requires oxygen
  • Thus incurring an oxygen debt
  • This is why we breathe heavily for a short time after vigorous exercise
  • Repays oxygen debt by converting lactic acid to glucose
• Aerobic respiration:

  • Complete breakdown of glucose to carbon dioxide and water
  • Following glycolysis the 2 pyruvate molecules breaks down into carbon dioxide and water
  • Requires oxygen
  • Occurs in mitochondria, on the folds of the inner membrane (larger SA)
• Aerobic respiration steps:

  • Each pyruvate converted to acetyl CoA
  • No ATP produced during this step
  • Each acetyl CoA enters citric acid cycle (Krebs cycle)
  • Releases CO2
  • 2 ATP produced (1 per acetyl CoA)
  • Resulting molecules enter electron transport system/oxidative phosphorylation where electrons pass between molecules
  • 34 ATP produced