Respiration

• Glycolysis is an anaerobic process
• Glycolysis Step 1: Phosphorylation

  • two molecules of ATP provide two phosphates which are attached to a glucose molecule to form hexose biphosphate
• Glycolysis Step 2: Lysis

  • the molecule is destabilised by the phosphorylation and then splits into two triose phosphate molecules
• Glycolysis Step 3: Phosphorylation:

  • another phosphate group is added to each triose phosphate to form triose biphosphate
  • the phosphates come from free inorganic phosphate ions located in the cytoplasm
• Glycolysis Step 4: Dehydrogenation

  • the triose biphosphate molecules are oxidised by the removal of hydrogen atoms to form two pyruvate molecules
  • NAD coenzymes accept the hydrogens and are reduced
  • the phosphates are used to form four ATP molecules
• matrix: contains enzymes for Krebs cycle and link reaction; also contains mitochondrial DNA
• outer mitochondrial membrane: separates contents of mitochondrion from rest of cell, creating a cellular compartment with ideal conditions for aerobic respiration
• inner mitochondrial membrane: contains electron transport chains and ATP synthase
• cristae: projections of inner membrane which increase the SA available for oxidative phosphorylation
• intermembrane space: proteins are pumped into this space by the electron transport chain. The space is small so the conc. builds up quickly
• Link reaction/Oxidative decarboxylation:

  • pyruvate enters the mitochondrial matrix by active transport
  • pyruvate then undergoes oxidative decarboxylation where carbon dioxide is removed along with hydrogen
  • the hydrogen atoms are accepted by NAD which is reduced
  • the remaining acetyl group is bound to coenzyme A to form acetyl-coenzyme A
  • Acetyl CoA delivers the acetyl group to the Krebs cycle
• Krebs cycle Step 1:

  • Acetyl CoA delivers acetyl to the Krebs cycle
  • the acetyl group combines with oxaloacetate (4C) to form citrate (6C)
• Krebs cycle Step 2:

  • the citrate molecule undergoes decarboxylation and dehydrogenation to produce one reduced NAD and carbon dioxide
  • a five carbon compound is formed
• Krebs cycle Step 3:

  • the 5C compound undergoes further decarboxylation and dehydrogenation reactions, eventually regenerating oxaloacetate
  • the cycle continues
• Oxidative Phosphorylation:

  • the hydrogen atoms collected by NAD and FAD are delivered to the electron transport chains in the cristae
  • hydrogen atoms dissociate into H+ and e-
  • the high energy electrons move into the ETC and reduce/oxidise electron carriers
  • energy is released as the electrons move along the transport chain
  • this energy is used to create a proton gradient leading to the diffusion of protons through ATP synthase, resulting in the synthesis of ATP
• Substrate level phosphorylation: production of ATP involving the transfer of a phosphate group from a highly reactive intermediate. It is different to oxidative phosphorylation.
• Lactate fermentation

  • pyruvate acts as a hydrogen acceptor, taking in hydrogen from reduced NAD, catalysed by lactate dehydrogenase
  • pyruvate is converted into lactate and NAD is regenerated
  • glycolysis continues so small quantities of ATP are synthesised
• Lactate fermentation cannot occur indefinitely because:

  • the reduced quantity of ATP would not be able to maintain vital processes for long enough
  • the accumulation of lactic acid causes a fall in pH leading to proteins denaturing
• Anaerobic respiration:

  • there is no oxygen to act as the final electron acceptor after the ETC so the flow of electrons stops
  • ATP synthesis through chemiosmosis stops
  • reduced NAD and FAD are no longer oxidised so they cannot be regenerated as NAD and FAD
  • the Krebs cycle comes to a halt as there are no coenzymes available
• Alcoholic fermentation:

  • irreversible
  • can occur indefinitely
  • pyruvate is converted to ethanal by pyruvate decarboxylase
  • ethanal accepts a hydroen from reduced NAD to become ethanol
  • NAD continues to act as a coenzyme
• RQ = CO2 produced/ O2 consumed
• RQ carbohydrates = 1
• RQ Proteins = 0.9
• RQ Lipids = 0.7
• lipids contain a greater proportion of carbon-hydrogen bonds than carbs so they produce much more ATP in respiration. They also require more oxygen to break them down, and release less CO2
• repiratory pathways