Ms. Nutter
Toothpick Lab Report
Abstract
Enzymes are an important type of protein that act as biological catalysts. One enzyme,
amalyse, catalyzes the breakdown of starch into glucose for digestion by humans and
other animals. In this lab, we used our hands and toothpicks to model the action of
amylase in order to investigate the factors that affect enzyme function. We measured the
rate of the reaction, which we defined as the number of toothpicks broken per minute,
under different conditions. We found that the type of substrate has the greatest effect on
lowering the rate of reaction, while enzyme concentration had the greatest effect of
increasing the rate of reaction.
Introduction
Enzymes are a type of protein that act as biological catalysts, which means they
help speed up the rate of reactions that occur in living organisms. They do this by being
highly specific – each enzyme has only one type of substrate with which it interacts. The
enzyme and its corresponding substrate interact at the enzyme’s active site, where the
enzyme then converts the substrate into the products of the reaction.
One specific enzyme we have studied is called amylase. Amylase is found in our
saliva and other digestive juices, and it interacts with the substrate starch. Starch is a
carbohydrate found in plants, and it provides humans and other animals with energy.
However, starch is a large, long molecule that cannot be digested by humans. Amylase
catalyzes the breaking of starch into smaller molecules of glucose, which we can then
digest and use for energy.
In this lab, we investigated different factors that may affect the ability of the
enzyme amylase to break down starch molecules. We used our hands and toothpicks to
model the action of amylase – our hands represented the enzyme, and the toothpicks
represented starch molecules. We measured our “enzyme” activity by the rate of the
reaction that it catalyzed, which we defined as the number of toothpicks broken per
minute. We looked at the effects of temperature, active site shape, concentration, and
substrate type on the rate of the reaction. I hypothesized that temperature, which we
represented by holding our hands in ice water, would have the greatest effect on the rate
at which our enzyme could break starch molecules, by decreasing the rate of reaction. I
also hypothesized that the concentration of enzyme, which we represented by having
three people work together as enzymes, would have the greatest effect of increasing the
rate of reaction.
Methods
This lab was conducted at six different stations by six groups of students. Within
each group, one person was designated the “enzyme,” in order to control for the effect
that using different people as enzymes might have on the rate of reaction. At each station,
the “enzyme” was timed for 15 seconds while they attempted to use their thumbs and
index fingers to completely break as many toothpicks as possible. They could only break
one toothpick at a time. This number was then multiplied by 4 in order to get the rate of
reaction in toothpicks per minute.
At the first station, the “enzyme” broke as many toothpicks as they could in 15
seconds. This served as the control for the experiment, because it measured the rate of
reaction of our enzyme under normal circumstances.
To measure the effect of temperature on the rate of reaction, at station 2, the
“enzyme” stuck their hands into a bowl of ice water for 30 seconds, dried them with a
paper towel, and then attempted to break as many toothpicks as possible in 15 seconds.
At station 3, duct tape was used to tape down the thumbs of the “enzyme,” which
was meant to model the effect of a change in the active site of an enzyme. They were
then timed for 15 seconds while they broke as many toothpicks as possible.
The effects of concentration on the rate of reaction were measured at two stations.
First, at station 4, 10 toothpicks were randomly dispersed across the bench top, and the
“enzyme” was timed for 15 seconds while they attempted to break as many as possible.
Next, at station 5, three group members served as “enzymes” and work together to break
as many toothpicks as possible in 15 seconds.
The last station investigated the effect of the substrate on the rate of reaction. At
this station, cotton swabs were used in place of toothpicks to represent a substrate other
than starch. Again, the “enzyme” was timed for 15 seconds while they tried to completely
break as many cotton swabs as possible.
Our data were collected as the number of toothpicks broken per minute and
combined into a class data table. The average rate of reaction and the standard deviation
for each station was calculated and graphed in a bar graph.
Results
Changing the substrate to a cotton swab produced the slowest average rate of
reaction, which was 5.33 toothpicks per minute, with a standard deviation of 5.47. The
fastest average rate of reaction occurred when 3 enzymes worked together – the average
rate was 114 toothpicks per minute, with a standard deviation of 15.95. Under normal
circumstances at the control station, the average rate of reaction was 50 toothpicks per
minute, with a standard deviation of 15.75. Placing our enzyme in ice water decreased the
average rate of reaction to 32 toothpicks per minute, with a standard deviation of 8.39.
Decreasing the concentration of the substrate also decreased the average rate of reaction,
to 41 toothpicks per minute, with a standard deviation of 4.69. Finally, taping the
enzyme’s thumbs down decreased the average rate of reaction to 18 toothpicks per
minute, with a standard deviation of 4.9 toothpicks per minute.
Discussion and Conclusions
Although I hypothesized that temperature would have the greatest effect on
lowering the rate of reaction, it was actually changing the substrate (from a toothpick to a
cotton swab) that caused the greatest decrease in reaction rate. While our toothpick
represented the substrate starch, the cotton swab represented a different substrate, such as
a protein or a lipid. This demonstrates that enzymes are specific to their substrate, and are
unable to adequately break down other kinds of substrates.
Similarly, changing the shape of the active site (by taping down the enzyme’s
thumbs) also caused a decrease in the rate of reaction. Because the active site is the place
on the enzyme where the substrate binds, it makes sense that disrupting this site will have
a large effect on the rate of the reaction. If the substrate does not “fit” with the enzyme, it
is harder for the enzyme to break it. Some factors that could affect the shape of the active
site include temperature, pH, and genetic mutations within the enzyme.
While our data does show that cold temperatures decrease the activity of our
“enzyme,” the cold temperature did not decrease the rate of reaction as much as changing
the active site or changing the substrate did. This could be because decreasing the
temperature does not cause enough change in the enzyme (or the substrate) to
dramatically decrease the rate of reaction. In a future lab, it would be interesting to
investigate the way in which hot temperatures affect the rate of reaction.
Based on our control rate of 50 toothpicks per minute, changing the concentration
of the substrate also caused a small decrease in the rate of reaction. This is due to the fact
that if there are not many substrate molecules to be broken down, then the enzyme will
not have many reactions to catalyze, and all reactions will stop once the substrate has run
out.
On the other hand, I hypothesized that having more enzymes would cause the
largest increase in the rate of reaction, and this was confirmed. When a large amount of
substrate is present and there are more enzymes available (as modeled by having three
people act as enzymes), the rate of reaction dramatically increases. More enzymes
working together will yield more reactions, thus increasing the overall rate of reaction.
A future lab could also investigate the effect of substrate type and concentration
on the rate of reaction by mixing a pile of toothpicks and cotton swabs together, and
timing the enzyme for 15 seconds while it attempted to break as many molecules of
substrate as possible.
One possible factor that may have affected our data is that different people
serving as the enzyme were breaking the toothpicks in different ways. Therefore, the way
in which the toothpicks were broken did not remain controlled. This could have explained
the outliers we observed in the data at stations 1 and 2. Furthermore, it was unclear what
constituted a “broken” toothpick – whether it had to completely break into two pieces, or
whether it simply had to be bent. This confusion would have increased our rates of
reaction, because people may have reported more “broken” toothpicks than there actually
were.
In conclusion, this lab demonstrated that many factors, including temperature,
active site shape, concentration, and substrate type affect the activity of an enzyme and its
rate of reaction. This is important to understand because it demonstrates the idea that
enzymes need a specific environment in order to work properly. Enzymes play critical
roles in our bodies, such as helping us digest our food, or ridding our bodies of harmful
toxins, and changing the environment in which they are working can affect how well they
do their job.