B2- Cellular Respiration

• ATP is the link between energy releasing and energy requiring reactions
• Chemical energy from food is used to regenerate ATP from ADP and Pi
• Building up and releasing energy:

  
• Phosphorylation is when a phosphate is added and makes the molecule energy rich and more reactive.
• When the energy rich compound, glucose, is broken down it released energy which is used to make ATP from ADP+ Pi
• Respiration is and enzyme controlled process and is in 3 stages in cells:

  • Glycolysis,
  • Citric acid cycle,
  • Electron transport chain
• Glycolysis occurs in the cytoplasm and does not require oxygen. It is the breakdown of glucose to pyruvate
• There are two phases to glycolysis,

  • Energy investment,
  • Energy pay-off
• Description of glycolysis:

  1. Glucose becomes phosphorylated to form intermediate 1.
  2. Intermediate 1 is phosphorylated to form intermediate 2.
  3. Four molecules of ATP are generated as intermediate 2 forms two pyruvate molecules.
  4. Dehydrogenase removed hydrogen ions and electrons which combine with NAD to form NADH.
• Oxygen has to present to continue respiration into the 2nd and 3rd stage: Citric acid cycle and electron transport chain.
• Citric acid cycle is in the matrix of the mitochondria
• The pyruvate produced at the end of glycolysis becomes the substrate for stage 2
• Description of citric acid cycle:

  1. Pyruvate (3C) is broken down into acetyl group (2C). This combines with coenzyme A to form acetyl coenzyme A.
  2. Each acetyl group (2C) combines with oxaloacetate (4C), via coenzyme A to become citrate (6C). Coenzyme A can then be reused.
  3. Citrate (6C) is broken back down into oxaloacetate (4C) over a series of steps. Two more molecules of CO2 are released.
  4. Electrons and hydrogen ions continue to be removed from the respiratory substrate, binding with coenzyme NAD to form NADH. One molecule of ATP is generated
• Role or dehydrogenase:

  • To removed ions and electrons from respiratory substrates,
  • To pass hydrogen ions and electrons to coenzyme NAD to form NADH.
• Electron transport chain is in the inner membrane of the mitochondria.
• In the electron transport chain, energy is released and ATP synthase generates ATP.
• Stages of electron transport chain:

  1. Electrons are passed along the electron transport chain releasing energy that is used to pump hydrogen ions across the inner membrane of the mitochondria.
  2. The hydrogen ions then return to the matrix through the membrane protein, ATP synthase, causing it to rotate.
  3. The electron and hydrogen ions are now in low energy state and these combine with a molecule of oxygen.
• Oxygen is the final hydrogen and electron acceptor in the electron transport chain combining to form water