Video Transcript
A student is completing an
experiment studying the rate at which trypsin, an enzyme found in the human body,
breaks down proteins in a beaker of milk. They are running the experiment at
20 degrees Celsius with a pH buffer of pH nine. What changing conditions would most
likely speed up the rate of reaction? (A) Reducing the amount of light
the reaction is exposed to. (B) Decreasing the concentration of
trypsin. (C) Increasing the temperature to
37 degrees Celsius. Or (D) increasing the pH to 14.
For an enzyme-catalyzed reactions
such as this to take place, the substrate, in this case proteins, must physically
collide with the enzyme. Therefore, any condition which
increases the chances of the enzyme and substrate colliding will increase the rate
of the reaction. There are four main changes in
conditions that can do this. So let’s consider each one in the
context of this reaction.
The first is to increase the
concentration of the enzyme, which in this case is trypsin. The more trypsin molecules there
are in the reaction, the more likely each protein molecule is to collide with one
and therefore the higher the rate of reaction. This means we can rule out option
(B) because it’s talking about decreasing the concentration of trypsin, which would
actually have the opposite effect and decrease the rate of reaction.
The second change is to increase
the concentration of the substrate, which in this case is protein. This works in the same way as
increasing the trypsin concentration. The more protein molecules there
are in a reaction, the more they will collide with trypsin molecules and the higher
the rate of reaction. The third is to change the pH,
which is how acidic or alkaline the conditions are. You may recall that pH is measured
on a scale from one to 14, where pH one represents a very acidic environment and pH
14 represents a very alkaline environment. pH seven represents a neutral
environment, which is neither acidic nor alkaline.
All enzymes have an optimum pH. This is the pH at which the enzyme
catalyzes its chemical reaction at the highest rate. The further away the conditions are
from the optimum pH, the slower the rate of reaction. Because most body cells have a
neutral pH of around seven, most enzymes have an optimum pH of around seven too. For the experiment carried out in
the question, we’re told that a pH buffer of pH nine is used. We can therefore also rule out
option (D) because it suggests increasing the pH to the most alkaline value of
14. Any substantial change in pH like
this is likely to inhibit the enzyme’s activity and would therefore decrease the
rate of reaction.
We can also rule out option (A)
because although there are a few examples of enzymes in the human body which are
sensitive to light, it’s very dark inside the digestive system where trypsin is
active. So it’s highly unlikely to respond
to changes in light intensity.
The final changing conditions which
will increase the rate of an enzyme-catalyzed reaction is to increase the
temperature. At higher temperatures, both enzyme
and substrate molecules have more kinetic, or movement, energy. Meaning they will collide more
often because they’ll be moving around more and the rate of reaction will therefore
be higher. Humans have an average body
temperature of 37 degrees, so most enzymes in the human body, including trypsin,
will be adapted to work best at this temperature. Therefore, increasing the
temperature from 20 degrees up to 37 degrees will be very likely to speed up the
rate of the reaction. We can therefore conclude that the
correct answer is (C). Increasing the temperature to 37
degrees would be most likely to speed up the rate of reaction.
