Enzymes work like a lock and key. Enzymes are proteins that under
normal conditions have a certain shape (think 3D here) that fits the
target. The enzyme cannot physically bind with the wrong substrate in
a way that will carry out the required chemical reaction. This is why
enzymes under the wrong conditions, such as pH or temperature, cease
to function. They lose their special shape, or as like to think of
it, they unravel and become more like strings. "All enzymes are made
of protein; that is why they are sensitive to heat, pH and heavy metal
ions. Unlike ordinary catalysts, they are specific to one chemical
reaction. An ordinary catalyst may be used for several different
chemical reactions, but an enzyme only works for one specific
reaction."
http://www.purchon.com/biology/enzymes.htm
For a VERY basic clear example of how an enzyme works, you can go to
this site and play the animation, which shows amylase breaking up
starch.
http://www.tvdsb.on.ca/westmin/science/sbi3a1/digest/enzymes.htm
Another slightly more complex discussion of enzyme specificity from
Martin Chaplin and Christopher Bucke (Cambridge University Press,
1990) explains how enzymes not only target a specific sustrate but can
even target a distinct part of that substrate. If you read the bottom
of the quote here, you will see the mention about glucose oxidase only
being effective on glucose and not any other sugars, just what your
question is asking. "Enzymes have a number of distinct advantages
over conventional chemical catalysts. Foremost amongst these are their
specificity and selectivity not only for particular reactions but also
in their discrimination between similar parts of molecules
(regiospecificity) or optical isomers (stereospecificity). They
catalyse only the reactions of very narrow ranges of reactants
(substrates), which may consist of a small number of closely related
classes of compounds (e.g. trypsin catalyses the hydrolysis of some
peptides and esters in addition to most proteins), a single class of
compounds (e.g. hexokinase catalyses the transfer of a phosphate group
from ATP to several hexoses), or a single compound (e.g. glucose
oxidase oxidises only glucose amongst the naturally occurring
sugars)."
http://www.sbu.ac.uk/biology/enztech/whyenz.html
Your question doesn't seem to require a discussion of the chemical
reaction involved in enzyme action, but if you're interested in an
explanation, you can find it here, under the heading "The mechanism of
enzyme catalysis":
http://www.sbu.ac.uk/biology/enztech/mechan.html
I've provided an answer targeting the level of your question, as a
pretty general explanation. If you need more detail about chemical
mechanisms, please request a clarification before rating the answer.
Regards,
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