Video Transcript
The enzyme in the diagram has had
its active site irreversibly changed. What scientific term describes this
change?
This question asks us about an
irreversible change in the active site of an enzyme. To answer this question correctly,
let’s review the key points about enzyme structure and the active sites.
Enzymes are biological
catalysts. They increase the rate of chemical
reactions inside the organism without being changed or used up themselves. They can either work on one
substrate if the enzyme is breaking the molecule apart or more than one substrate if
joining them together. For this question, we will just
refer to one substrate.
Enzymes work by lowering the energy
required to make the reaction occur. Enzymes are therefore really
important, as many of our cellular reactions are too slow to happen by
themselves. For example, if we did not have
enzymes, then cellular respiration would not work at a fast-enough rate to provide
the energy we require for moving, breathing, digesting food, to name but a few. And we wouldn’t be able to
survive. Enzymes are therefore essential for
life.
But how do enzymes work? An enzyme is made up of one or more
polypeptide chains composed of many amino acids bound together. The order of amino acids along a
chain determines the overall 3D shape of the enzyme due to their interactions with
each other and the environment.
One specific area of the structure
is called the active site. And it is here that the substrate
binds. Each type of enzyme has its own
unique active site shape, and so it will only bind to one specific substrate.
But how do they bind? The substrate has a complementary
shape to the enzyme’s active site. You may wonder what this means. Well, it just means that the active
site and substrate fit together like the pieces of a jigsaw puzzle.
Enzymes have optimum conditions,
such as a specific range in temperature or pH, at which they work best. If the conditions change too much
from these optimum conditions, the bonds holding the structure together are
affected, which will lead to it breaking down. The shape of the active site will
change irreversibly, and it will no longer be able to bind to its substrate. The enzyme is said to be denatured,
or we say that denaturation has occurred. This results in the decrease in
rate, or stopping, of the reaction.
After reviewing the key facts about
enzymes, their substrates, and what kind of conditions can affect the shape of the
active site, we should now be able to answer our question correctly. The correct scientific term for
when an enzyme has had its active site irreversibly changed is denaturation.
