respiration

• Describe fully the link reaction, including details about all the products that are formed

  • link reaction occurs in mitochondrial matrix
  • pyruvate is converted to a molecule called acetate as a carbon is lost in the form of carbon dioxide via decarboxylation
  •  hydrogen atom is also lost from pyruvate, which is transferred to a molecule of NAD, a coenzyme, to produce reduced NAD, called NADH
  • a molecule called coenzyme A is added, which converts acetate into a new molecule called acetyl-CoA
• what is substrate-level phosphorylation ?

  • A molecule containing a phosphate group. This molecule donates a phosphate group to ADP
  • An enzyme to catalyse the reaction
• Describe fully the Krebs cycle, including details about all the molecules that are produced

  • Acetyl CoA produced in the link reaction enters the Krebs cycle, where it reacts with a molecule containing 4 carbons to produce citrate ( 6 carbons )
  • Coenzyme A is removed in this reaction.
  • a series of oxidation and reduction reactions occur , the 6-carbon molecule is converted back into the 4-carbon molecule
  • Carbon dioxide is produced via decarboxylation . In addition, for every acetyl CoA molecule that enters the Krebs cycle, one ATP molecule is produced as an ADP molecule reacts with a phosphate group. Also, intermediate molecules in the Krebs cycle lose hydrogen atoms, which reduces NAD and FAD to produce NADH and FADH2​ 
• Which stages of aerobic respiration take place in the mitochondria?

  Pyruvate is moved into the mitochondrial matrix by active transport. The link reaction and the Krebs cycle both take place in the mitochondria
• Using your knowledge of aerobic respiration, suggest how athletes are able to run for longer than two hours

  • glucose stores have been used up in aerobic respiration, triglycerides and amino acids can be used in respiration.
  • Triglycerides are broken down into glycerol and three fatty acids. Glycerol is converted into triose phosphate which takes part in glycolysis. The fatty acids are converted into acetyl CoA molecules that can take part in the Krebs cycle. The majority of amino acids with three carbons are converted into pyruvate which is used in the link reaction, whereas 4 and 5− carbon amino acids are converted into intermediates in the Krebs cycle.
  • using amino acids and triglycerides, ATP continues to be produced in the absence of glucose stores. This means ATP is available for use as an energy source for the contraction of muscles that allows the athlete to keep running.
• ’Hitting the wall’ is a phenomenon characterised by sudden fatigue and loss of energy after around two hours of running. Suggest an explanation for ‘hitting the wall’.

  triglycerides and amino acids must first be converted into a suitable form in order to be used in aerobic respiration. These reactions take time. ‘The wall’ is hit when there is a temporary depletion of ATP, before triglycerides and amino acids are used in respiration.
• In the last stage of aerobic respiration, describe the proton gradient across the inner membrane and how it is maintained

  There is a higher concentration of protons in the intermembrane space compared to the matrix, which establishes a proton gradient across the inner membrane.To maintain the proton gradient, protons are actively transported from the matrix to the intermembrane space.
• Describe the stages of oxidative phosphorylation.

  In oxidative phosphorylation, electrons supplied by reduced NAD and reduced FAD are transferred through the electron transfer chain via a series of oxidation-reduction reactions.Next, these oxidation-reduction reactions provide energy to the electron transfer chain. As a result, protons move from the matrix to the intermembrane space via active transport. This ensures that a proton gradient is maintained across the inner membrane.Additionally, the electrons in the final inner membrane protein react with oxygen and protons to form water. Through this reaction, oxygen is also known as the final electron acceptor.Finally, chemiosmosis through ATP synthase results in the production of ATP.
• describe what happens in the first stage of glycolysis

  1. Glucose enters the cell’s cytoplasm.
  2. an enzyme adds two phosphate groups to glucose via phosphorylation.
  3. phosphate groups are available due to the breakdown of two ATP molecules.
  4. this produces a new molecule called glucose phosphate.
• describe how oxidation-reduction is involved in glycolysis

  Triose phosphate loses hydrogen in the third step of glycolysis, so triose phosphate is oxidisedThis hydrogen is transferred to a molecule called NAD, forming NADH or reduced NAD
• Describe the process of glycolysis. Ensure that all products formed are mentioned

  1.  glucose enters the cell’s cytoplasm.
  2. an enzyme adds two phosphate groups to glucose in a process known as phosphorylation.
  3. phosphate groups available due to breakdown of 2 ATP molecules.
  4. this produces a new molecule called glucose phosphate.
  5. glucose phosphate breaks down into two molecules of triose phosphate
  6. triose phosphate is converted into pyruvate. In this step, 2 molecules of NADH and 4 molecules of ATP are formed.
  7. The overall yield of ATP within glycolysis is 2 ATP.