Video Transcript
With reference to enzymes, what
does “denatured” mean? (A) The enzyme’s protein structure
has been stretched. (B) The enzyme has been damaged and
subsequently works more slowly. (C) The enzyme has been killed. (D) The enzyme’s active site has
been irreversibly changed. Or (E) the enzyme has been used as
much as it can be and must be replaced.
This question is asking about
denaturation of enzymes. To answer it, let’s review some key
facts about the structure of enzymes and how changes in the environment can affect
them.
Enzymes are biological catalysts,
which means that they increase the rate of chemical reactions inside the organism
without being changed or used up themselves. Substrates are the molecules going
into the reaction, and products are what are formed. Enzymes can either work on one
substrate if the enzyme is breaking the molecule apart, for example, pepsin in the
stomach, which breaks down protein in our food, or they can work on more than one
substrate if joining them together, for example, DNA ligase, which is important in
DNA replication. For this question, we will just
refer to one substrate.
An enzyme is made up of one or more
polypeptide chains composed of many amino acids bound together. It is therefore a biological
molecule and is not living. So we can rule out option (C)
because if it is not alive, it cannot be killed.
The order of amino acids along the
polypeptide chain determines the overall 3D shape of the enzyme due to their
interactions with each other and the environment. This shape is very important in the
function of the enzyme as to speed up the reaction, the enzyme must be able to bind
with the substrate. The substrate binds the enzyme at a
special area called the active site. The shape of the active site is
complementary to the shape of the substrate, which means they fit together like
jigsaw pieces. This forms an enzyme–substrate
complex. The reaction can then occur, and
the products are released. The enzyme then binds to another
substrate as it is not altered or used up during the reaction. This means we can also discount
option (E).
Enzymes have optimum conditions,
such as a range in temperature or pH, that they work best at. When enzymes are subjected to high
temperatures or extreme changes in pH, their structure can be altered. This is because these conditions
will break the bonds holding the amino acids together and also disrupt the
interactions between the amino acids. This means that the 3D confirmation
is altered and the shape of the active site becomes irreversibly changed.
Now that we have discussed
denaturation in detail, let’s look back at our question. We now know that the correct answer
is (D). “Denatured” means that the enzyme’s
active site has been irreversibly changed.
