Enzyme
<p><b >Enzymes</b> (<img src="/f0b41cc0-635f-57b4-8514-4b42fdd33cb1.png"/> <a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English#Key" title="Wikipedia:IPA for English" >ˈɛnzaɪmz</a><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/</a>) are biological molecules that <a href="http://en.wikipedia.org/wiki/Catalysis" title="Catalysis" >catalyze</a> (i.e., <a href="http://en.wikipedia.org/wiki/Reaction_rate" title="Reaction rate" >increase the rates</a> of) <a href="http://en.wikipedia.org/wiki/Chemical_reaction" title="Chemical reaction" >chemical reactions</a>.<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Enzyme#cite_note-0" >[1]</a></sup><sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Enzyme#cite_note-1" >[2]</a></sup> </p>
<p>
In enzymatic reactions, the <a href="http://en.wikipedia.org/wiki/Molecule" title="Molecule" >molecules</a> at the beginning of the process, called <a href="http://en.wikipedia.org/wiki/Substrate(biochemistry)" title="Substrate (biochemistry)" class="mw-redirect" >substrates</a>, are converted into different molecules, called <a href="http://en.wikipedia.org/wiki/Product(biology)" title="Product (biology)" >products</a>. </p>
<p>
Almost all chemical reactions in a <a href="http://en.wikipedia.org/wiki/Cell_(biology)" title="Cell (biology)" >biological cell</a> need enzymes in order to occur at rates sufficient for life. </p>
<p>
Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which <a href="http://en.wikipedia.org/wiki/Metabolic_pathway" title="Metabolic pathway" >metabolic pathways</a> occur in that cell.</p>