Coenzymes, Cofactors and the Chemistry They Supply · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How small helpers support enzymes

Science · Biochemistry & Molecular Biology · ages 19-20
Name ______________________   Date ____________

  1. What can magnesium contribute when an enzyme binds a phosphate-containing substrate?

    • Stabilisation of charged phosphate groups
    • Transfer of an acetyl group through a coenzyme A bond
    • Acceptance of electrons through conversion of NAD+ to NADH

  2. Which statement describes coenzymes?

    • They are inorganic metal ions that cannot contain carbon
    • They are organic cofactors that supply additional chemistry
    • They are protein side chains joined permanently into every enzyme

  3. Which group does ATP transfer in a kinase reaction?

    • An acetyl group carried through coenzyme A
    • Electrons carried through reduction of NAD+
    • A phosphoryl group

  4. An enzyme requires a cofactor. What is its protein component called when that cofactor is absent?

    • The holoenzyme, already complete with its required helper
    • The apoenzyme, lacking its required cofactor
    • The coenzyme, an organic helper distinct from the protein

  5. A vitamin B3 deficiency reduces the supply of NAD. Which effect follows most directly?

    • NAD-dependent redox reactions may be impaired
    • Every reaction that transfers electrons must stop completely
    • Coenzyme A must lose its ability to carry acetyl groups

  6. Which statement correctly describes the reuse of coenzymes?

    • Every coenzyme is discarded after its first reaction and cannot be regenerated
    • Every coenzyme remains chemically unchanged during every reaction it supports
    • A coenzyme can change chemically and later be regenerated

  7. A student claims magnesium, zinc and iron help enzymes only by changing oxidation state. Which correction fits their different roles?

    • They have distinct roles; not every metal helper performs redox chemistry
    • The claim holds because every metal helper must transfer electrons in every reaction
    • Only organic helpers affect chemistry; metal ions cannot participate in enzyme function

  8. A vitamin B1 deficiency reduces TPP availability. Which reaction is directly vulnerable because it requires TPP?

    • Phosphoryl transfer from ATP to glucose in a kinase reaction
    • Pyruvate decarboxylation within pyruvate dehydrogenase
    • Electron acceptance by NAD+ in every NAD-dependent reaction
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Answer key

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

How small helpers support enzymes W1-mt_CZ2ytn3SQr-s1

  1. Stabilisation of charged phosphate groups · Magnesium can stabilise charged phosphate groups. The other actions describe organic carriers.
  2. They are organic cofactors that supply additional chemistry · Coenzymes are organic cofactors, distinct from the enzyme's protein side chains.
  3. A phosphoryl group · Kinases can transfer a phosphoryl group from ATP to their substrate.
  4. The apoenzyme, lacking its required cofactor · The apoenzyme is the protein component without its required cofactor.
  5. NAD-dependent redox reactions may be impaired · Reduced NAD supply can impair reactions that depend on NAD, not every redox reaction.
  6. A coenzyme can change chemically and later be regenerated · Reuse can involve regeneration after a chemical change rather than staying chemically unchanged throughout.
  7. They have distinct roles; not every metal helper performs redox chemistry · Magnesium can stabilise phosphate charges and zinc can activate water; iron can participate in redox chemistry.
  8. Pyruvate decarboxylation within pyruvate dehydrogenase · TPP derives from vitamin B1 and supports pyruvate decarboxylation within pyruvate dehydrogenase.
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