Intracellular and extracellular enzyme-catalysed reactions

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An enzyme that catalyses a reaction **inside** the cell that produced it (e.g. a **respiration** enzyme).

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An enzyme that is **secreted** and catalyses a reaction **outside** the cell (e.g. a **digestive** enzyme).

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To **release** the enzyme out of the cell, through the membrane, into the surroundings.

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A **respiration** enzyme (or catalase breaking down hydrogen peroxide inside the cell).

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A **digestive** enzyme such as **amylase, protease or lipase** — or the enzymes a decomposer secretes onto dead matter.

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Because a large food molecule (e.g. starch, protein) is **too big to cross the cell membrane**; it must be broken into small soluble subunits first.

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It **hydrolyses** it into **small, soluble subunits** (e.g. starch → maltose/glucose) that **can be absorbed**.

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They **secrete extracellular enzymes** onto dead matter, digest it **externally**, then **absorb** the small soluble products.

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**No** — both intracellular and extracellular enzymes are globular proteins that **lower activation energy**, are **specific** and are **reusable**. Only the location differs.

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Its **activity appears outside the cell** (e.g. in the surrounding liquid / culture medium), acting on a substrate the cell has not absorbed.

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A linked series of enzyme-controlled reactions where the **product of one reaction is the substrate of the next** — run by intracellular enzymes.

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**Intra** = inside; **extra** = outside — so intracellular acts **inside** the cell and extracellular acts **outside** it.