Respiration

• Respiration is a series of enzyme controlled reactions which produce chemical energy in the form of ATP. Can be done aerobically (with oxygen) or anaerobically (no oxygen).
• what is meant by the term phosphorylation?

  Adding a phosphate group to a molecule.
• What are the two types of phosphorylation?

  1. Oxidative phosphorylation - occurs during aerobic respiration where ATP is formed in the electron transport chain
  2. Substrate level phosphorylation - the formation of ATP by the direct transfer of a phosphate group.
• Coenzymes bind with a specific enzyme or substrate, helping to catalyze a reaction. Coenzymes transfer a chemical group (like hydrogen) from one molecule to another.
• Coenzymes in respiration

  • NAD - transfer H+ from one molecule to another (so can oxidise to reduce a molecule)
  • FAD - transfers H+ from one molecule to another
  • Coenzyme A - transfers acetate between molecules
• 4 stages of aerobic respiration

  1. Glycolysis
  2. The link reaction
  3. Kreb Cycle
  4. Oxidative phosphorylation and the electron transport chain
• Structure of the mitochondria

  
• Glycolysis is the first stage of both aerobic and anaerobic respiration and takes place in the cytoplasm of the cell.
• Steps of Glycolysis:

  1. Phosphorylation - Glucose (6c) is phosphorylated by 2 ATP to form Hexose bisphosphate (6c)
  2. Lysis - Hexose bisphosphate (6c) is split to form 2 molecules of triose phosphate (3c)
  3. Oxidation - hydrogen is removed from each molecule of triose phosphate and transferred to coenzyme NAD to form 2 reduced NAD
  4. Dephosphorylation - phosphates are transferred from the intermediate substrate molecules to form 4 ATP through substrate-linked phosphorylation
  5. Pyruvate is produced - the end product of glycolysis which can be used in the next stage of respiration
• How does pyruvate enter the mitochondria from the cytoplasm of the cell?

  1. When oxygen is available, pyruvate will enter the mitochondrial matrix and aerobic respiration will continue.
  2. Pyruvate moves across the double membrane of the mitochondria via active transport, this requires a transport protein and a small amount of ATP
• Where does the link reaction take place?

  Matrix of the mitochondria
• Steps of the link reaction

  1. Pyruvate is oxidised by enzymes to produce acetate and carbon dioxide
  2. This requires the reduction of NAD to NADH
  3. Combination with coenzyme A to form acetyl coenzyme A (acetyl CoA)
• What is the Kreb cycle?

  The Krebs cycle (sometimes called the citric acid cycle) consists of a series of enzyme-controlled reactions where reduced enzymes and ATP is produced.
• Steps of the Kreb Cycle

  1. Decarboxylation of citrate - releasing 2 CO2 as waste gas
  2. Oxidation (dehydrogenation) of citrate - releasing H atoms that reduce coenzymes NAD and FAD
  3. Substrate-linked phosphorylation - a phosphate is transferred from one of the intermediates to ADP, forming 1 ATP
• What is Oxidative phosphorylation?

  ATP production
• What are the 2 processes in oxidative phosphorylation?

  1. Electron Transport Chain
  2. Chemiosmosis
• Steps in Oxidative Phosphorylation

  1. Reduced NAD and FAD release hydrogen atoms

  2. Hydrogen atoms break up into protons and electrons

  3. The electrons enter the electron transport chain (ETC)

  4. The electrons are taken up by the electron carriers in the ETC

  5. The electrons move along from carrier to carrier, each carrier the electrons release energy

  6. The energy from electrons is used to pump protons

  7. The released energy at each carrier is used by the electron carriers to pump H+ from the mitochondrial matrix into the intermembrane space

  8. Protons diffuse from the intermembrane space to the matrix, down the electrochemical gradient

  9. Protons are unable to diffuse through the phospholipid bilayer, so instead go through ATP synthase

  10. Proton movement provides potential energy causing phosphorylation of ADP

  11. The electrons leave the last electron carrier and pass into the matrix, where and are accepted by oxygen

  12. H+ also joins, forming water – a product of respiration
• Electrochemical gradient


  Forms as a result of the pumping of protons from the mitochondrial matrix into the intermembrane space
• Chemiosmosis

  The movement of protons from the intermembrane space to the matrix, down the electrochemical gradient
• How can fats be used as a respiratory substance?

  • Triglycerides are made up of fatty acids and glycerol.
  • Glycerol is 3C which is phosphorylated and converted to triose phosphate - entering glycolysis.
  • Fatty acids are broken down into 2C fragments which combine with coenzyme A to form Acetyl coenzyme A.
• Why do fats produce a large amount of ATP?

  Fatty acids can be very long chains that can be hydrolysed to form many 2C fragments and hydrogen atoms can be used to produce ATP during oxidative phosphorylation.
• How can protein be used as a respiratory substance?

  • In cases of starvation, tissue proteins are hydrolysed to amino acids.
  • Amino acids are deaminated by the liver
  • The remaining molecules enter the respiratory pathway at different points depending on number of carbon atoms.
• What is anaerobic respiration?

  Anaerobic respiration is the incomplete intracellular breakdown of glucose or other organic compounds in the absence of oxygen. Stopping at glycolysis.
• In eukaryotic cells what 2 types of anaerobic respiration occurs?

  1. Alcoholic fermentation - in plants and yeast
  2. Lactate fermentation - animals
• What consequences when there is not enough oxygen available for respiration:

  • There is no final acceptor of electrons from the electron transport chain
  • The electron transport chain stops functioning
  • No more ATP is produced via oxidative phosphorylation
  • Reduced NAD and FAD aren’t oxidised by an electron carrier
  • No oxidised NAD and FAD are available for dehydrogenation in the Krebs cycle
  • The Krebs cycle stops
• Oxidation


  Loss of electrons (gain of oxygen, loss of hydrogen)
• Reduction

  Gain of electrons (loss of oxygen, gain of hydrogen)
• Dehydrogenation/Oxidation

  Removal of hydrogen (using dehydrogenase enzymes)
• Decarboxylation

  Removal of carbon (using decarboxylase enzymes) to form Co2