Gluconeogenesis and the Reciprocal Regulation of Opposing Pathways · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Building sugar without going backward

Science · Biochemistry & Molecular Biology · ages 20-21
Name ______________________   Date ____________

  1. Which bypass mapping is correct? G6Pase, FBPase, PC and PEPCK are the enzyme abbreviations defined in the lesson.

    • Hexokinase: G6Pase; PFK-1: FBPase; pyruvate kinase: PC + PEPCK
    • Hexokinase: PC + PEPCK; PFK-1: G6Pase; pyruvate kinase: FBPase
    • Hexokinase: FBPase; PFK-1: PC + PEPCK; pyruvate kinase: G6Pase

  2. Why does gluconeogenesis need different reactions at three glycolytic steps under usual cellular conditions?

    • Direct reversal is unfavourable, so alternative bypass chemistry is needed
    • Every glycolytic reaction reverses favourably, but different names require new enzymes
    • Glycolytic enzymes cannot interact with any six-carbon sugar under cellular conditions

  3. Which group lists established gluconeogenic carbon sources in humans?

    • Acetyl CoA alone, with all its carbon converted directly into net glucose
    • Inhaled carbon dioxide alone, fixed into glucose without an organic precursor
    • Lactate, glycerol and glucogenic amino acids

  4. Fructose 2,6-bisphosphate rises in a liver cell. Which direct regulatory effects are expected?

    • It inhibits PFK-1 while activating FBPase, favouring the opposite regulatory direction
    • It activates PFK-1 while inhibiting FBPase
    • It activates PFK-1 and FBPase equally, increasing both opposing reactions together

  5. PFK-1 and FBPase complete 7 paired turns in one cell, with equal opposing sugar flux. Each paired turn restores fructose-6-phosphate. What is the net cost?

    • 7 ATP consumed with no net sugar conversion
    • 14 ATP consumed because both reactions consume one ATP per turn
    • 7 ATP produced because restoring the sugar also restores the spent ATP

  6. In the Cori cycle, how can lactate carbon from working muscle return as glucose?

    • Blood carries lactate to the liver, which can make glucose
    • The lungs exhale lactate unchanged, then muscle reabsorbs it as glucose
    • Muscle turns every lactate molecule directly into glucose without liver involvement

  7. In humans, carbon supplied only as acetyl CoA from even-chain fatty acids can replace lactate as a net glucose precursor.

    Circle one:   True   False

  8. A liver cell lacks G6Pase, but PC and PEPCK remain active. Which missing bypass can those two enzymes not replace?

    • Pyruvate to PEP, because PC and PEPCK never participate in that route
    • Fructose-1,6-bisphosphate to fructose-6-phosphate, because G6Pase normally performs it
    • Glucose-6-phosphate to free glucose
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Building sugar without going backward W1-mt_D1MbKcb6Le-s1

  1. Hexokinase: G6Pase; PFK-1: FBPase; pyruvate kinase: PC + PEPCK · G6Pase and FBPase bypass the two phosphorylation reactions; PC and PEPCK jointly bypass pyruvate kinase.
  2. Direct reversal is unfavourable, so alternative bypass chemistry is needed · The thermodynamic difficulty of direct reversal motivates alternative reactions, some of which use additional energy coupling.
  3. Lactate, glycerol and glucogenic amino acids · The named sources can supply glucose carbon. Triglyceride glycerol is one reason a blanket exclusion of fat is inaccurate.
  4. It activates PFK-1 while inhibiting FBPase · Its opposite effects on PFK-1 and FBPase are an example of reciprocal regulation.
  5. 7 ATP consumed with no net sugar conversion · Each paired turn consumes one ATP. Seven turns consume seven ATP while returning the sugar to its starting form.
  6. Blood carries lactate to the liver, which can make glucose · The cycle connects muscle lactate production with liver glucose production through the circulation.
  7. False · Acetyl-CoA carbon from even-chain fatty acids does not give net glucose in humans. Glycerol and odd-chain propionyl carbon are separate cases.
  8. Glucose-6-phosphate to free glucose · G6Pase performs the glucose-6-phosphate bypass. PC and PEPCK perform a different bypass at pyruvate kinase.
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