Respiration

• Aerobic respiration


  1. Glycolysis

  2. Link reaction

  3. Krebs Cycle

  4. Final stage

  5. Electron transfer chain
• Glycolysis

  • Happens at cytoplasm
  • Happens for both aerobic and anaerobic
  • Does not need oxygen
  • Glucose is converted into 2 pyruvate molecules
  • Phosphorylation via enzyme produces hexose bisphosphate molecules
  • Phosphates are available due to the break down of 2 ATP molecules down to 2 ADP molecules
  • Phosphate groups are added to prevent the diffusion of glucose outside the cell as the concentration is higher, this also prevents the molecules from leaving through the transport proteins
  • Hexose bisphosphate are converted into 2 triose phosphate molecules
  • Both triose phosphate molecules are converted into pyruvate and 4 ATP molecules are formed along with it
  • Additional 2 phosphates are added to the molecules
  • Overall yield of 2 ATP molecules are formed
  • Triose phosphate is reduced and the hydrogen goes into NAD to become reduced NAD (NADH)
• Link reaction

  • Pyruvate molecules move into the mitochondrial matrix for aerobic respiration
  • Via co-transport facilitated by active transport - needs energy and transport protein
  • Energy is not given by ATP
  • Pyruvate loses a carbon and becomes acetate
  • Carbon becomes carbon dioxide via decarboxylation and leaves the body
  • Hydrogen is also oxidised via dehydrogenation and is used to produce NAD + H → NADH
  • NAD is a coenzyme
  • Acetate joins to coenzyme A (Co A) and becomes acetyl coenzyme A (acetyl-co A)
  • Basically an enzyme
  • Used to just produce the enzyme and to link to the next stage of respiration
• Krebs Cycle

  1. Acetyl-CoA reacts with oxaloacetate to form Citrate

  2. CoA which is recycled back in the link reaction

  3. Citrate is converted back into oxaloacetate

  4. 2 carbons are lost as CO2

  5. ADP is converted into ATP called substrate-level phosphorylation - during glycolysis and Krebs cycle

  6. Dehydrogenation of citrate - oxidation causes for NAD to become reduced into NADH

  7. FAD - coenzyme - also takes up two hydrogens and is reduced into FADH2
• Products of each stage

  • Glycolysis: 2 ATP molecules, 2 Pyruvate molecules
  • Link reaction: 2 Acetyl CoA, 2 CO2, 2 NADH
  • Krebs Cycle: 2 CoA, citrate (then is used up), 4 CO2, 2 NADH, 2 FADH2, 2 ATP
• Final stage

  1. ATP is formed in the inner mitochondrial membrane through an enzyme ATP Synthase

  2. Energy is provided by H+ ions

  3. High concentration in the inner mitochondrial membrane than matrix - proton gradient

  4. Protons move down the electrochemical gradient via chemiosmosis using the enzyme

  5. During this ATP molecules are formed through the catalyst

  6. Gradient is then also maintain as the H+ ions are actively transported back into the intermembrane space
• Electron transfer chain

  1. NADH and FAADH2 transfers a pair of electrons - becoming oxidised

  2. The reduced proteins are then transferred along through oxidation-reduction reactions

  3. This allows the proteins to actively transfer protons back into the intermembrane space - allows for a concentration gradient

  4. Final electron acceptor is oxygen which has a stronger force attraction to electrons

  5. NADH becomes NAD and a proton

  6. FADH2 becomes FAD and two protons

  7. NAD and FAD are recycled back into the previous cycles
• Oxidative phosphorylation


  • From the oxidation of NADH and FADH2
  • Ends at the formation of ATP
• Single glucose molecule


  • Mitochondria adaptation for respiration: large surface area of the cristae which are folded up inner mitochondrial membranes
  • Large surface area allows for more oxidative phosphorylation
  • Cristae can vary in different cells due to functions
• Anaerobic respiration


  1. Glycolysis

  2. Pyruvate formation in cytoplasm

  3. Varies in different organisms
• Animals

  Pyruvate becomes lactate
• Plants and microorganisms

  Pyruvate becomes ethanol and CO2
• Lactate and ethanol formation

  • Allows for glycolysis to happen although they are harmful
  • Allows for ATP to be produced
• Lactate formation

  1. Pyruvate is reduced by hydrogen

  2. NADH oxidised to provide for the hydrogen - NAD is formed

  3. NADH is produced by the conversion of triose phosphate

  4. Triose phosphate → pyruvate → lactate
• NAD is recycled in the glycolysis stage to ensure ATP is continuously produced
• Ethanol and carbon dioxide formation

  1. Pyruvate is reduced and NADH is oxidised

  2. NADH is provided when triose phosphate or glyceride-3-phosphate is converted into pyruvate

  3. Ethanol is produced as a result and CO2
• Respiratory substances

  • Proteins
  • Lipids
  • Carbohydrates
• Respiratory substances


  • Lipids > Proteins > Carbs in terms of energy produced
• Hydrogen atoms react with co enzymes

  Co enzymes are then used to accept electrons from the electron transfer chain and then be re used
• Lipids release the most hydrogen atoms
• Oxygen reacts with the respiratory substances

  To form CO2 and water
• Respiratory quotient

  Oxygen consumption over carbon dioxide released
• Proteins RQ


  More oxygen to break down, approx 0.9 so less
• Lipids RQ

  Even more oxygen, approx 0.7 so even less
• If there are more C-H bonds the RQ will be lower
• aerobic respiration

  1. glycolysis
  2. link reaction
  3. krebs cycle
• anaerobic respiration

  1. glycolysis
  2. lactate formation or ethanol + carbon dioxide formtion
• mitochondria adaptation for respiration:

  • large surface area of the cristae which are folded up inner mitochondrial membranes
  • large surface area allows for more oxidative phosphorylation
  • cristae can vary in different cells due to functions
• glycolysis:

  • happens at cytoplasm
  • happens for both aerobic and anaerobic
  • does not need oxygen
• Glucose conversion

  Converted into 2 pyruvate molecules
• Phosphorylation via enzyme

  Produces hexose bisphosphate molecules
• Phosphate availability

  Due to the break down of 2 ATP molecules down to 2 ADP molecules
• Phosphate groups added

  To prevent the diffusion of glucose outside the cell as the concentration is higher, this also prevents the molecules from leaving through the transport proteins
• Hexose bisphosphate conversion

  Converted into 2 triose phosphate molecules
• Triose phosphate conversion

  Converted into pyruvate and 4 ATP molecules formed along with it
• Triose phosphate reduction

  Hydrogen goes into NAD to become reduced NAD (NADH)