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

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

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

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

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

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

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

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