Investigating Enzymes


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.

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