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Spending ATP to make ATP: glycolysis and the link reaction questions

The structure of ATP and the hydrolysis of its terminal phosphate, releasing about 30.5 kJ per mole; where the four stages of respiration happen; glycolysis as phosphorylation, lysis and oxidation, giving a net 2 ATP, 2 reduced NAD and 2 pyruvate per glucose; the link reaction in the matrix, with decarboxylation, dehydrogenation and the formation of acetyl coenzyme A; and a running tally of the products so far.

6 original questions · 20 marks · the spending atp to make atp: glycolysis and the link reaction notes · Respiration and cellular energy

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• 4 marks · Describe

  Describe what happens during glycolysis, using the terms phosphorylation, lysis and oxidation, and give the net yield per molecule of glucose.

  Mark scheme

  1. B1 phosphorylation: two molecules of ATP are hydrolysed and their phosphate groups added to glucose, giving hexose bisphosphate, which is less stable and more reactive
  2. B1 lysis: the six-carbon hexose bisphosphate splits into two three-carbon molecules of triose phosphate, so everything after this point happens twice per glucose
  3. B1 oxidation: hydrogen is removed from each triose phosphate and taken up by NAD, giving two reduced NAD per glucose, and pyruvate is what remains
  4. B1 phosphate groups are transferred directly from the intermediates onto ADP by substrate-level phosphorylation, making four ATP per glucose, so the net yield is 2 ATP, 2 reduced NAD and 2 pyruvate

• 4 marks · Calculate

  Eight molecules of glucose pass through glycolysis in a cell. Calculate the number of molecules of ATP produced, the number used, the net gain in ATP, and the number of molecules of reduced NAD formed.

  Mark scheme

  1. M1 per molecule of glucose, glycolysis produces 4 ATP, uses 2 ATP and forms 2 reduced NAD
  2. A1 4 × 8 = 32 molecules of ATP produced
  3. A1 2 × 8 = 16 molecules of ATP used, so the net gain is 32 − 16 = 16 ATP
  4. A1 2 × 8 = 16 molecules of reduced NAD

• 4 marks · Describe

  Describe what happens to a molecule of pyruvate during the link reaction, and give the products of the link reaction per molecule of glucose.

  Mark scheme

  1. B1 pyruvate is carried from the cytoplasm across both mitochondrial membranes into the matrix by a transport protein
  2. B1 it is decarboxylated: one carbon is removed and released as carbon dioxide, which is the first carbon dioxide respiration produces
  3. B1 it is dehydrogenated: hydrogen is removed and taken up by NAD, giving one reduced NAD
  4. B1 the two-carbon acetyl group left behind joins coenzyme A to form acetyl coenzyme A, and because the reaction runs twice per glucose the products are 2 CO₂, 2 reduced NAD and 2 acetyl CoA, with no ATP made

• 3 marks · Explain

  Explain why ATP is a suitable immediate source of energy for a cell, when the complete oxidation of glucose releases roughly 2880 kJ per mole.

• 3 marks · Suggest

  A mature red blood cell has neither a nucleus nor any mitochondria. Suggest how such a cell still makes ATP, and suggest what limits the amount of ATP it can obtain from each molecule of glucose.

• 2 marks · State

  State where in a cell glycolysis takes place, and state where the link reaction takes place.

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