An enzyme is a biological catalyst made up from protein. Catalysts are chemicals or substances that speed up a reaction, however they are not affected themselves whilst doing this. An enzyme has an active site, which has a unique shape into which a substrate of the exact unique shape can fit.
There is a carbohydrase enzyme in our saliva. It is called amylase. Amylase breaks down starch into sugar (glucose).
Amylase
Starch Sugar
The reason why I believe that amylase and starch work best together is because each enzyme has its specific substrate to breakdown…which in this case, amylase is breaking down starch. Enzymes are made of protein causing it to be a specific shape. Therefore the shape of the enzyme and the substrate must fit together, like a key fits into a key whole, and will then start reaction.
I will be given 2g of amylase before I will start my experiment so that I can vary that given amount into the certain concentrations I am going to use in my experiment. I will be using a five-point range of concentrations, which will be 0.01g, 0.02g, 0.03g, 0.04g and 0.05g. The substrate (starch) concentration will be kept constant at a mass of 0.5g mixed with 30cm³ of distilled water. I will make the substrate solution by the masses above of starch and distilled water mixed together. Then once my solution is ready I will add the amylase to start the reaction. As soon as the enzyme is added to the solution the stopwatch will start timing the reaction. Before the reaction has actually started I will add 2 drops of iodine into each dimple in a dimple tray (spotting tile). Every minute I will take out samples of the reaction and place them into a dimple using a pipette. I will carry on using this method every minute until eventually the colour of the iodine does not turn black/blue. This will show that there is no more starch present, as the enzyme has broken it down. If there was starch present then the iodine colour will turn black/blue. Once the colour of the iodine resumes its normal self then I will stop the stopwatch and plot down the time taken for the amylase to break down the starch. I will repeat the experiment using different concentrations/masses of amylase each time. To get average reliable results I will repeat each experiment with the same concentration 2 times.
I am going to keep my experiment a fair test by controlling all of the variables except one…the enzyme concentration. The apparatus I will need during the experiment will be; dimple tray, iodine, 2g of amylase, starch, distilled water, measuring cylinder, pipette, stop watch, test tube, test tube rack, weighing scale, beaker and spatula. Also I might need goggles just for safety if needed, however, when using iodine goggles must be worn, as iodine can be irritable to the eyes.
When we first tried out the experiment using 0.1g, 0.2g, 0.3g, 0.4g, 0.5g of amylase it took quite some time to obtain a reaction and therefore we changed the masses to 0.01g, 0.02g, 0.03g, 0.04g, 0.05g and it gave us reasonable results. Therefore we selected masses of amylase around these figures. We were given a little bit more enzymes to get these measurements as the 2g that was given to us at the beginning had finished so we needed more to obtain new measurements. We also tried out certain measurements for the substrate solution. We used 5g of starch with 20cm³ of distilled water; however, this quantity was not good enough as it caused a very slow reaction. It caused a slow reaction because there was more substrate for the enzyme to break down. Therefore more time was needed for the reaction to be completed. There were also another two slow reactions taken place when we used 2g of starch with 20cm³ of distilled water and 1g of starch with 20cm³ of distilled. Finally when we tried out 0.5g of starch with 30cm³ of distilled water it gave us a suitable reaction time and therefore we chose this measurement for our substrate concentration. These were our preliminary tests that helped us to decide our measurements for the masses/concentrations of both the enzyme and substrate concentrations.
PREDICTION: I believe that if the enzyme concentration is increased then the time taken for the amylase to break down starch will decrease and the rate of reaction will increase. This is because once I add more enzymes to the reaction there will be more active sites available for the substrate to react upon…therefore the reaction will speed up and there will be a decrease in the time taken. Enzymes speed up chemical reactions…no matter what kind of enzyme it is as long as its substrate is the right one with the right specific unique shape to fit into the enzyme. Therefore once the amylase and starch is mixed together there will be a reaction as they will be bumping into each other…. and they will bump into each other more rapidly once there will be more active sites (enzymes) for the starch to bump into. This will prove that the time taken will decrease and the rate of reaction will increase as the enzyme concentration increases too.
DIAGRAM:
A B C D E
0.01g 0.02g 0.03g 0.04g 0.05g
Starch, amylase and distilled water
Enzyme Concentration
Spotting tile containing 2 drops of iodine
RESULTS:
CONCLUSION: From my results above it is clear that my experiment was perfect and ended with exact predicted results…no anomalies what so ever! This proves that the results I achieved during this experiment support my prediction as I predicted that if I increase the enzyme concentration the time taken for the enzyme to breakdown its substrate will decrease. This statement is proven to be true as once the enzyme concentration is increased there will be more active sites for the substrate to react upon. It is like feeding starving children with chocolate…if there is more children (enzyme) to feed then the chocolate (substrate) will be finish quicker than if there was only 2 children to feed! So if there is more amylase (enzyme) for the starch (substrate) to feed (react) upon then the starch will disappear sooner and quicker and the rate of reaction will increase as the time taken will decrease!
As you can see from my graph, there is a straight blue line through the x-axis which shows that I kept the enzyme concentration constant throughout the experiment. The pink line shows the time taken for the reaction to be completed (y-axis) against the enzyme concentration (x-axis). The time taken for the reaction is decreasing as the enzyme concentration is increasing…just as I predicted!
EVALUATION: I trust that my experiment went fairly well as there were no anomalies at all, which proves that nothing went wrong and everything ended relatively well. However, there were a bit of struggles in controlling the experiment, for instance, when I had to take out samples from the reaction to see if the starch was broken down or not it was rather difficult to manipulate as I had to time every minute and sometimes things went wrong like the pipette was dirty or the dimple tray had to be refilled etc. But in general our results have been brilliant. I could have made certain improvements if I had a chance to repeat the whole experiment again! These improvements would be to organize everything before the experiment e.g. apparatus….so that you will be in control and ready for any sudden reactions! Secondly I would repeat the experiment more than twice, maybe three or four times to obtain absolute reliable results and averages. And thirdly I would use more ranges of amylase concentrations e.g. 0.01g, 0.02g, 0.03g, 0.04g, 0.05g, 0.06g, 0.07g, 0.08g, 0.09g, 0.10g…a ten point range rather than a five point! I would have used a larger range if only I had more amylase to separate into certain concentrations.
My results are reliable but if I had repeated them more than I did then of course they would be even more reliable…the more the repeats the more reliable the results! But in general my results are good enough…they support both my prediction and the scientific knowledge that I have obtained.
If I were to do an extension to my experiment I would vary the temperature as this variable has an enormous effect on an enzymes rate of reaction. This is because enzymes can only react or become activated at certain temperatures (body temperature – between 35ºc to 37ºc), and if the temperature is either too low or too high the enzymes will not respond. If the temperature is increased too much then the enzymes will become denatured and will not be able to work what so ever…also if the temperature is too low it will become frozen and again will not be able to work. So I believe that this variable, temperature, is also a very good variable to vary in an enzyme experiment. There are a few more variables that could be used as an extension, such as the Ph of an enzyme, the substrate concentration etc. all of these factors have great effects on enzymes and their rate of reactions.
