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Module 1: Enzimas

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Enzimas - introducción

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XSIQ
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Biology - Enzymes - Introduction

Enzymes - Introduction

An enzyme: showing its active site.

Enzyme action.

(Enzymes end in "-ase"; e.g. proteases act on proteins, lactase acts on
lactose)

* Nearly all are composed of _protein_ molecules - long polypeptide
chains folded and curled into a 3D shape, with an active site into which
fits the specific substrate; e.g. sucrase acts on sucrose. The substrate
molecule and the active site [1] adjust to fit, according to the induced
fit hypothesis.

Normally, an intracellular enzyme is _specific_ in its action; that is,
it will act only on one substrate. For example, proteases in the digestive
system act on proteins in food, but not on the proteins making up the gut
wall. Some extracellular enzymes act on a number of substrates. For
example, pancreatic lipase acts on several types of fats.

* each has its _optimum_ (best) conditions in which it functions; for
example, temperature, pH

* enzymes are _denatured_ by conditions outside their range; i.e. the
active site [2] becomes distorted and will no longer fit the substrate

* _water_ is essential for enzyme activity

* enzymes are assisted by _coenzymes [3]_ and _cofactors_

* enzymes can act in either direction; that is, they are _reversible_ in
their action

* enzymes can be _re-used,_ as they are not destroyed by the reactions
they catalyse

* many reactions occur in a _series_ of stages (metabolic pathways), with
each step being catalysed by a particular enzyme. The absence of any one
enzyme means that the reaction cannot proceed to the next step

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