Investigating Enzymes Essay, Research Paper
Research Enzymes
exist in all living things. They are composed of polymers of amino acids and
are produced in living cells. Each cell contains several hundred enzymes, which
catalyse a vast number of chemical reactions. Enzymes are known as Biological
Catalysts as they dramatically increase the rate at which reactions occur
within living organisms, without being ?used up? or effecting the reaction in
any other way. Enzymes catalysis saves the need for an increase in temperature
in order to speed up reactions within living things. Such an increase in
temperature would be lethal to the organism. In
this investigation I intend to explore the one of the factors that effect the
rate of enzyme catalysis. My research from textbooks and the Internet suggests
that this depends on several factors; temperature, pressure, pH and
concentration. After research and careful consideration, I have decided to
first look at how a change in temperature could affect the rate of reaction. In
order to design a suitable experiment and make a credible prediction, I must
first explore more closely how temperature is likely to affect the rate of
catalysis. Enzymes are specific – they only control one type of reaction;
therefore I must use one specific enzyme in my experiment, in order to find a
clear way of measuring the rate of reaction. Although they are specific, all
enzymes work in a very similar way and have similar properties. They are all
globular proteins and are all biological catalysts, they increase the rate of a
given reaction without being used up and their presence does not change the
nature of the reaction or the end product. Enzymes work by having an active
site, made from amino acids. Here, substrate molecules will bind with the
enzyme (and other substrate molecules if necessary) and a reaction takes place.
The enzyme itself is not affected and releases the new chemical after the
reaction. After release of the end product, more substrate molecules can bind
with the active site. Enzymes
can catalyse anabolic reactions or catabolic reactions (involved in breakdown).
The diagram above shows an anabolic reaction. In a catabolic reaction, the reverse
would happen. Using
the information gained here together with my knowledge of kinetic theory, it is
possible to understand how temperature affects the rate of reaction. Kinetic
theory states that when a substance is heated, energy is given to the particles
and they speed up. Therefore when heat is applied to an enzyme and substrate,
the particles speed up, increasing the rate at which they bind with each other.
This would suggest that the rate of reaction should increase as the temperature
is increased. This is not quite true, as there is a limit to the temperature at
which an enzyme can work because excessive heat causes an enzyme to become
denatured and stop working. Also, there is a minimum temperature at which an
enzyme can function. Every chemical reaction requires activation energy in
order to get started. Although enzyme catalysis greatly reduces this, some
energy is still required. Because of this the reaction is still unable to
happen below a given temperature (this varies depending on the type of enzyme
and reaction, as does the maximum temperature). If warmed to above the
activation temperature, an enzyme will work again as normal. A denatured
enzyme, however, is damaged and will not work again even if cooled below the
optimum temperature. Prediction I
predict that the rate of reaction will increase as the temperature increases
until the reaction reaches an optimum temperature. Above this optimum
temperature, the rate of reaction will fall to zero very quickly, as the enzyme
denatures. I must now conduct an experiment to test my prediction. I will do
this using the enzyme catalyse. Catalyse is found in most living organisms. It
speeds up the catabolic reaction, which breaks down hydrogen peroxide into
oxygen and water. Apparatus Using
my information on catalyse, it is clear that one of the products of the
reaction is oxygen. Therefore to measure the rate of reaction, I could measure
the rate at which oxygen is produced. For this experiment I will need: Leek
as the source of catalyse Hydrogen
peroxide A
water bath in which I can heat both enzymes and substrate Thermometers
to ensure both liquids are at the correct temperature Measuring
cylinders in order to measure the amount of oxygen produced, as well as
the amount of yeast/hydrogen peroxide used A
timer to enable me to work out the rate at which oxygen is produced A
basin of water Conical
flask in which the reaction will take place Bung
and delivery tube Method To
test my prediction I will heat the catalyse and hydrogen peroxide to a given
temperature and allow them to react in the conical flask, starting the timer at
the beginning of the reaction. The oxygen given off will pass through the
delivery tube and bubble up into the measuring cylinder, which will be set full
of water in a basin. I will allow the reaction to continue for a set period of
time before using the measuring cylinder to measure the amount of oxygen
produced. The results will then be recorded in a table, and then graphed after
the experiment has been conducted at a satisfactory amount of temperatures. My
preliminary experiment suggests that suitable quantities to use would be 20cm3
hydrogen peroxide and 10cm3 leek, timed over a period of one minute
during the reaction. I am now able to perform the experiment at a range of
temperatures between 0degrees and 80degrees. If the rate of reaction is still
above zero beyond 80degrees, I will continue the experiment for higher
temperatures. My research suggests however that most enzymes become denatured
before 80degrees. Fair Testing To
make sure this experiment is a fair test, the only factor I must vary must be
temperature. This means that I have to keep the concentrations, pressure and pH
of the substance constant throughout the experiment. In order to ensure
accuracy, I will conduct the experiment three times for each temperature and
take a mean result to plot on the graph. The exact quantities used must first
be determined by a preliminary experiment. Results Conclusion Several
points can be drawn from the results of this experiment. The first is that the
graph is very similar to that of my prediction. It clearly shows an optimum
temperature at which the catalyse will work, with an increase/decrease either
side. I was surprised at the way the rate of reaction slowed above the optimum
temperature. I had expected there to be a very sharp decline as soon as the
optimum temperature was surpassed. This was the case, but the rate of decline
slowed at one point, which contradicts my research. This may be due to an
inaccuracy in my experiment, as my research suggests that enzymes fail to work
after becoming denatured. Another
thing that can be learned from the results is that the speed at which the rate
of reaction increases as the temperature rises seems to become greater. Between
10degrees and 20degrees the increase is equal to the original rate of reaction,
whereas between 20degrees and 30degrees, the increase is double the original
rate of reaction. However, the increase in the rate of reaction seems to slow
again between 30degrees and 40degrees. This could be for several reasons; that
this is exactly what is supposed to happen and the rate of reaction does slow
again when close to the optimum temperature, or that the optimum temperature
lies somewhere between 30degrees and 40degrees and that the rate of reaction
has reached it?s optimum temperature and is slowing again by the time the
temperature reaches 40degrees. In any case, I would have to investigate this
further in order to reach a firm conclusion as to the reason this graph appears
to show slowing of the increase in the rate of reaction between these points. I
believe these results can be explained in the same way as my prediction, as the
prediction was on the whole correct. Because the particles move faster as heat
is applied, they bind with the enzymes quicker and more often so the rate of
reaction speeds up. When the optimum temperature is surpassed, the enzymes
begin to denature and cease to function, causing the rate of reaction to slow. The
reaction will never stop completely, as hydrogen peroxide will break down
naturally, even with no working enzymes present. Evaluation The
data obtained in this experiment supports my conclusion well, although there
were some results and trends that I couldn?t explain. This may have been due to
inaccuracies in the way the experiment was performed, or that I need to further
my knowledge in order to explain the results. I
am convinced that the results show there is a correlation between the increase
in temperature and the increased rate of reaction. This correlation would have
been easier to work out had my measurements been slightly more accurate. The
accuracy of these measurements could be improved by the use of a burette
instead of a measuring cylinder, as it is a more precise piece of equipment and
there are fewer margins for error. Another source of error may have been in the
water baths, as they were supposed to be set at fixed temperatures to heat up
the substances. One had to be very careful that the substances did not exceed
their planned temperatures of there was danger of denaturing. The experiment on the
whole was a success, but it could be improved by the use of more accurate
equipment and better organisation. Several assumptions had to be made in this
experiment. When such assumptions are made, further work needs to be carried
out to check these assumptions. I had to assume that all enzymes worked in the
same way, but further work could be done with different enzymes and reactions
to check this. Through the experiment, I measured the rate of reaction at
10degrees intervals. I think that further work should be done between 30degrees
and 40degrees in an attempt to find the exact optimum temperature for the
enzyme catalyse. Work between these temperatures would allow me to plot a more
accurate graph and explain the apparent slowing in the increase of the rate of
reaction between these two temperatures in my current results.