The other type of enzyme is known as the intracellular enzymes, which speed up chemical reactions going on inside our cells.
Enzymes do more than just speeding up reactions; they also control them and make sure that reactions take place in the correct place and at the correct time.
Enzymes have five main properties
1. They are proteins- all enzymes are made from proteins
2. They are specific- Each enzyme controls a specific reaction and will only act on certain substrate.
3. They can be reused- enzymes remain unchanged throughout reactions,so they can be used over and over again.
4. They become deformed by heat-.almost all enzymes become denatured, when the temperature rises above a certain temperature. This means they change shape and no longer work.
5. They are sensitive to ph- most enzymes work best in neutral conditions, however digestive enzymes work best in acidic conditions and enzymes in the small intestine work best in alkaline conditions.
As I have said enzymes are very specific and the diagram below shows exactly how they are though to work.
Molecules are constantly moving and colliding with one another. When the substrate molecule collides into the correct enzyme, it fits perfectly into the active site of the enzyme. This is known as “lock and key”, as the substrate fits into the active site of the enzyme like a key fits into a lock, and as you need the correct key for a certain lock, the correct enzyme is needed for a certain substrate.
After the reaction has taken place, the products leave the active site, freeing it for another substrate molecule.
However, when an enzyme is destroyed by heat, the active site of the enzyme changes shape, so that the substrate can not fit into it.
The optimum tempearure of an enzyme is the tempearature at which
Apparatus
Thermostatically controlled water bath
Test tubes
Splints
Pieces of photographic film
Stopwatch
Enzyme solution (protease)
Syringe
Glass rod
Ph paper
Beaker
Safety
Safety goggles will be worn at all times, to prevent any of the protease from damaging our eyes
Hair will be tied back and lab coats will be done up
The enzyme itself will be handled with care, whilst being put in and taken out of the water baths.
Some of the water baths may be very hot, and extra care will be taken to ensure no accidents involving this hot water.
Fair test
The pieces of photographic film used will always be roughly the same size and taken from the same role of film.
The concentration of the protease will remain the same at 0.5%
The volume of the protease solution will be kept constant at 10cm3
All the test tubes containing the protease solution will be kept in the water bath for 3 minutes before placing in the photographic film, to make sure that they have reached the required temperature.
In order to truly know how long the action on the photographic film took, the transparent piece of photographic film obtained from the preliminary experiment, will be used to compare with the pieces of photographic film under investigation.
To make sure that the results are reliable, two repeats of each temperature will be carried out.
Variables
Independent variable-temperature
Dependant variable- rate of reaction
Controlled variables are temperature, ph, and concentration of enzyme, concentration of substrate and volume of enzyme.
Temperature- in most reactions, as the temperature increases, so does the rate of the reaction and if the temperature decreases, so does the rate of the reaction. This is because, as the temperature increases, the amount of energy increases causing the molecules to vibrate and move around more, therefore increasing the number of successful collisions between the substrate and the enzyme. However, this only happens to a certain extent, as after the enzyme reaches its optimum temperature, it will slowly change shape and become denatured.
The shape of an enzyme molecule is very important, as it has to fit its substrate exactly. When the temperature increases above 60 degrees, the shape of the enzyme changes and no longer fits into its substrate. This is one of the many reasons that organisms can be killed if exposed to high temperatures for a long period of time. The enzymes in their bodies become denatured and the daily chemical reactions that would usually take place at a faster rate become very slow and the successful maintenance of life stops.
Ph
Most enzymes work best at a certain ph. Other alkaline or acidic conditions may alter the chemical properties of enzymes.
For example, the protein digesting enzyme in the body works best at an acidity of ph 2. However, at this ph, amylase (the enzyme from saliva) cannot work at all.
Most enzymes work best in neutral conditions. The ph at which an enzyme works best is known as its optimum ph.
Concentration of enzyme
The rate of an enzyme reactions depend on the concentration of the enzyme and its substrate. The more of the enzyme molecule produced in a cell, the faster the reaction will take place, as long as there are enough substrate molecules available.
Likewise, the higher the concentration of the substrate the faster the reaction, providing there are enough enzyme molecules to handle the extra substrate. Once again this is due to the number of successful collisions taking place. If the concentration increases, there will be more molecules, more successful collisions, therefore a higher rate of reaction.
Volume of enzyme
Method
The apparatus will be set up as shown in the diagram and 10cm3 of protease will be placed in a test tube using a syringe. A syringe is an accurate form of measurement and will provide me with the absolute correct amount of solution. This solution will be placed in a water bath at the required temperature for 3 minutes before adding the photographic film. To ensure that the photographic film stays fixated in the test tube and to allow me to compare it to the previous piece of film, I will take a splint and split it, slotting in the piece of film. This will ensure that it is secure and will remain secure throughout the experiment. The splint will be placed in the test tube after 3 minutes. However, to make sure I have a repeat of this temperature, instead of having only one splint in the test tube, I will have two.
The time will be recorded by a stopwatch and I will wait by this water bath and check its transparency every 15 seconds. After I am sure that it has gone completely transparent, I will stop the stopwatch and record the results.
I will do exactly the same for the remaining for temperatures. however, if the film does not become transparent after 10minutes then I shall note down that the enzyme has denatured. After completing the experiment, I will take some ph paper and place it in the test tubes of protease to ensure that the ph is constant in all and is a suitable ph for the enzyme to work in.
Diagram
Mock results table
Mock graph
Obtaining evidence
In general the results obtained seem to support my prediction, however I will know whether this is true once I have drawn the two graphs.
Whilst collecting the results I followed all my safety rules in order to prevent any accidents. The method stated in my plan was followed almost exactly to obtain the most reliable results.
The control variables stated in my plan were controlled:
The pieces of photographic film used were roughly the same size and were taken from the same roll of film.
The protease enzyme was taken from the same batch, which meant that its concentration was kept constant for each experiment at 0.5 %.
The same volume of protease was used each time- 10.0cm3
The ph of the protease wasn’t controlled but it was tested to ensure accurate results and according to my results the ph was constant at 7.
Controlling these variables will have made my results reliable and will give me an accurate graph.
Graph(see paper)
Analysis
Up to 55°C, the rate of reaction of the hydrolysis of sucrose increased. As the temperatures rose the molecules moved faster (kinetic theory). In this reaction, this meant that enzyme and substrate molecules collided more frequently so that more enzyme-substrate complexes were formed and more products were produced.
Above 55°C the rate of reaction decreased rapidly with increasing temperatures. This occurred because rising temperature supplied enough energy to break some of the bonds between molecules. The heat caused a change in shape of the sucrase protein molecule so that it became denatured. The active site was altered, preventing the enzyme from locking onto its substrate preventing the formation of an enzyme-substrate complex and the production of any products (glucose and fructose).
Evaluation
In general, the procedure I followed did work and gave me reliable results that supported my prediction. The results showed a definite trend, once again supporting my prediction. I was lucky and in this case, none of my results were anomalous which proves how well planned the experiment was and how accurately the method was followed.
The procedure was fairly well planned, but there were certain areas at which problems could have risen. Firstly, it was not completely evident when the photographic film had gone transparent, as while it remained in the protease filled test tube, the transparency of the photographic film is not evident. In order to check the transparency, it has to be lifted out of the enzyme, therefore perhaps making the results less reliable.
It was not easy to judge the end point, at which the film went clear, but once it was taken out I compared it to another piece of photographic film, which had gone transparent, to make sure this had too.
In order to improve this, I could somehow have use an electronic device to measure the exact amount of light entering the piece of film, to check its actual transparency. However, it would be very difficult to come across this time of equipment in a school.
In order to extend the experiment further, I could carry out a similar experiment investigating the effect of temperature of the action of a different protease, say pepsin on a photographic film. This is because; I could then compare the effect of a bacterial enzyme against a human one.
I could also use a wider range of temperatures, to add detail and to be able to draw a more accurate graph based on the results. In addition I could investigate more temperature around the optimum temperature, to find the exact temperature at which the enzyme is most efficient.
In order to make the results more reliable I could also do more repeats, or do repeats in separate test tubes, unlike the experiment that I carried out. Both repeats were in the same test tube, which means they could be classed as not repeats, however If I were to carry out repeats in two different test tubes, I would get similar results anyway.
