AQA Chapter 12 - Respiration

• 1st Stage of both Aerobic and Anaerobic respiration
• It occurs in the cytoplasm outside of the mitochondria
• It does not require oxygen
• Requires ATP to start the process (similar to a match)
• It occurs in all living cells
• It occurs because a glucose molecule is too big to enter mitochondria and a mitochondrion does not have the correct carrier molecules in order to transport it into the cell

• Called phosphorylation as it adds 2x phosphate in order to make glucose unstable and cause lysis (splitting)
• Uses 2ATP and converts it into 2ADP
• Results in Glucose Biphosphate
• Glucose splits into 2x Triose Phosphate molecules

• The second stage is known as Oxidation
• It is the use of NAD to produce NADH+
• Dephosphorylation occurs after this step which converts the Triose Biphosphate into Pyruvate which is used in the first step of the link reaction

• It occurs in the mitochondrial matrix
• It uses 3 carbon pyruvate and converts it into Acetyl CoA
• It produces CO2

• 3 Carbon Pyruvate is Decarboxylated and Dehydrogenated which produces CO2 and Reduced NAD
• From this, Acetate is formed (2 Carbon)
• Coenzyme A is then reacted with the Acetate to form Acetyl CoA
• Acetyl CoA is then used in the Krebs Cycle

• Occurs in the mitochondrial matrix
• The Krebs Cycle can occur twice per glucose molecule or twice per pyruvate molecule
• Carbon Dioxide is released as a waste gas

• Acetyl CoA (2-carbon) is reacted with a 4-carbon molecule to form Citric Acid (6-carbon)
• CO2 is released to form a 5-carbon molecule
  
• NAD+ also is reduced to form NADH & H+
  
• CO2 is released again, forming a 4-carbon molecule
  
• FAD (a cousin to NAD) is reduced
  
• ATP is produced from ADP
  
• This cycle is repeated with another Acetyl CoA molecule

Only a small amount of ATP is produced by the Krebs cycle. The vast majority of potential energy is carried away from the Krebs cycle by reduced NAD & FAD to later be converted to ATP

• The electron transport chain is located on the inner mitochondrial membrane
• At every stage in respiration, electron-carrying molecules are produced (FADH+NADH)
• The electron transport chain is the physical place in the mitochondria where Oxidative Phosphorylation occurs
• Oxidative Phosphorylation requires both Oxygen and Electron Carriers
  

• Electron Carrying molecules such as NADH + FADH carry electrons which are accepted by the electron transport chain
• This allows the active transport of H+ ions into the intermembrane of the mitochondria
• This causes the H+ ions to be in high concentration in the intermembrane space and causes a diffusion gradient between the intermembrane space and the mitochondrial matrix
• The only way for the H+ ions to diffuse back is through ATP synthase 
• This causes ADP+Phosphate => ATP
• Oxygen acts as a final electron acceptor, producing water as a waste product

• In anaerobic conditions Oxidative Phosphorylation and the Krebs Cycle cannot occur
  
• Without Oxygen, the final electron cannot be accepted in Oxidative Phosphorylation, so no oxidised NAD/FAD is cycled back to the Krebs cycle
• Glycolysis still occurs as it requires no oxygen to function
  
• Reduced NAD, without aerobic respiration to accept its hydrogen ions and electrons, donates them to pyruvate molecules
• This produces Lactic Acid in animals
• Oxygen is eventually required as Reduced NAD is oxidised in anaerobic respiration so eventually all the Reduced NAD would be used
  

• In aerobic respiration in plants, the donation of hydrogen ions and electrons to pyruvate forms Ethanol and CO2
• This process has been used for thousands of years to produce alcohol
• Aerobic respiration is not efficient for producing ATP, only producing 2 ATP molecules rather than 32 ATP