The Effect of PH on Enzyme Activity

The Effect of PH on Enzyme Activity
Enzymes are known as biological catalysts. They are widely used in today?s world to alter or speed up the rate of reaction without themselves being changed. Enzymes are globular proteins which act as catalysts. A catalyst is a chemical substance, which speeds up the rate of reaction. For an example in the human body there are several thousands of chemical processes going and the quicker these happen the better it is, so enzymes are produced to increase the rate of reaction
Every biological process has it own enzyme especially designed for the process e.g. In the process of digestion salivary glands produce an enzyme called amylase in the saliva this enzyme starts the break down of starch. So enzymes are specific for one process. -?????????????????????????????????- All enzymes work their best at an optimum PH or temperature. These means that for enzymes to work effectively they have to be in the right conditions. All enzymes have different optimum levels. So enzymes work best at a:
Particular level of acidity or alkalinity (PH)
Particular level of temperature ( oC)
The graph below shows this: [image] Enzyme Activity increasing [image] Temperature or PH Increasing Enzymes can also become denatured. This means that enzymes will be destroyed if the conditions become too inappropriate. -???????????????????????????????- Enzymes will denature at High temperatures usually above 45 oC and enzymes will also denature in extreme conditions of PH, as some enzymes are sensitive to this. -???????????????????????????????- When referring to enzymes here are the definitions used: The substance that enzymes act on is the substrate. The substance formed by the reaction is the product The site on which the enzyme takes place is called the active The enzyme that will be used in this investigation is called Catalase. Catalase is present in the blood and prevents a build of dangerous peroxide. If a small piece of liver is added to hydrogen peroxide a rapid evolution of oxygen is seen. -?????????????????????????????????- Catalase is an extremely affective catalyst. One molecule of catalase will decompose forty thousand molecules of hydrogen peroxide a second. -????????????????????????????????? prediction Before carrying out this experiment I shall make a prediction. I predict that the particular enzyme I shall use will work best at a certain pH and at the opposing pH levels the enzyme will react insufficiently. I predict this because my knowledge of science enables me to say that all enzymes work their best at a certain pH, so needless to say that this enzyme would definitely have an ideal pH. I also predict than the enzyme will work at an ideal pH with in a small range. Regarding my graph I predict that the graph will be of a shape that I have shown in the beginning. I predict this because the enzyme, catalase will work as shown in the graph. method For this investigation I shall be measuring the rate of reaction by measuring the amount of froth that appears when Hydrogen Peroxide reacts with liver with a certain pH being used each time. The pH range I will be using will be from 2.2 to 9. The Enzyme, Catalase is present in the blood and hydrogen peroxide has the formula of 2H2O2, which consists of water and oxygen when it is broken down by catalase. Here is a list of the apparatus I will require to carry out this investigation.
Safety goggles
Measuring cylinders x2
Hydrogen Peroxide (20.0ml will be required each time)
Universal indicator
Liver (1.0gram to be used each time)
Stop watch
Hydrochloric acid
Measuring scales (measure amount of liver)
Ruler (cm) (in case froth over flows)
plan Here is now how I plan to do this investigation.
Initially I will pour 20.0ml of hydrogen peroxide into the
measuring cylinder which I will move down so that precise
millilitres of substance is added each time.
Then I will add 2/3 drops of universal indicator to the hydrogen
peroxide and write down the colour of the solution because this
will ensure me that I am using the write pH at each time.
I will then add 1.0 gram of liver and instantly press the button
on the stopwatch. I will now measure the rate of reaction by
measuring the amount of froth; I get in a standard amount of
The results will be placed in a table as shown: pH Colour of universal indicator Time (seconds) Starting volume of froth cm3 Finishing volume of froth cm3 Difference in volume cm3 Rate= volume/time 2.2 60 3 60 4 60 5 60 6 60 7 60 8 60 9 60
This procedure will be repeated with fresh liver will be used each
time. With the adding of dilute acid or alkali and noting the
colour I get.
At the end of each experiment I shall pour the peroxide and liver
into the bucket where it will be put be safely deposited.
Fair Test As I am doing this experiment I will have to keep it a fair test. This means that the variables will have to be kept the same each time otherwise inappropriate results may occur and other readings being taken would be at an unfair disadvantage. So to make this experiment a fair test I shall keep the same amount of: ? Hydrogen peroxide (20.0ml) ? Liver (1.0g) ? Time (60 seconds) ? Universal indicator (2/3 drops) I shall only change the pH each time because the whole of the investigation is to find out what effect pH has on enzyme activity. In carrying out these procedures I believe that my test will be fair and anomalies will be kept to a minimum. Accuracy In doing this investigation I intend to make my results as accurate as possible. To achieve this I shall make sure that the cylinders are washed each time and there are no substances left in the cylinder. I shall also make sure correct amounts of peroxide is used every time and that the liver is the correct mass my using measuring scales. To make my results as a whole more accurate I shall do the experiments three times so then I know that if my results are similar then the evidence is more reliable because in the first experiment an error may have occurred. I will plot a mean value for the results I get. Safety When I am doing this experiment I must consider the safety issues that may arise to my attention. I have considered how I shall under go this experiment and therefore summed up the safety measures that should be in placed to prevent any injury or damage. These are: ? Safety goggles must be worn to prevent splashes of any substances in the eyes ? The environment should be made clear with surfaces clear, bags and coats and stools placed in relevant places ? We should also be careful with the substances that will be used. Hydrogen peroxide is a corrosive substance so eye protection must be worn and concentrations of the substance must be kept low so there is not a harmful, extreme reaction. If substance is swallowed then the casualty?s mouth should be washed out and he or she should be given a glass or two of water and if the liquid gets in eyes or skin the area affected should be flooded with water. Where the problems occur medical attention must be on hand. ? Apparatus used such as measuring cylinders and beakers should be checked for any cracks as they could cause substances to spill. Results Here now are the results I collected whilst doing my experiment PH Colour of universal indicator Time (seconds) Starting volume of froth cm3 Finishing volume of froth cm3 Difference in volume cm3 Rate= volume/time 2.2 Red 60 22 67 45 0.75 3 Red 60 26 88 62 1.03 4 Orange/yellow 60 30 87 57 0.95 5 Yellow 60 23 132 109 1.82 6 Yellow 60 28 121 93 1.55 7 Green 60 22 122 100 1.67 8 Green 60 28 110 82 1.37 9 Green 60 22 105 83 1.38 Graph of results is shown next page. Analysis of results The results I have collected tell me that without a doubt the pH of the solution does affect the rate of enzyme activity. My results show me that the enzyme works at a particular ?optimum pH?. My results display that at pH 4 the enzyme works at it?s greatest this must be obviously be the optimum pH in which the enzyme is kept or within a small range of 4 such as 3 or 5 also the enzyme denatured and will at pH 13 and above. From my results I can explain them with a view in mind of the theory of science. I can say that the enzyme works within a certain optimum pH and that the pH affects the activity of the enzyme, which is why at different PH?s the enzyme did not work best and denatured. On my graph where there is a certain peak, this peak shows the optimum pH, which is 5. This can be related to science because enzymes are suited to a certain pH. Regarding my prediction I believe that I predicted correctly. I predicted that the enzyme would have worked best at a certain pH and the opposing levels the enzyme would react insufficiently. I can back this up or relate it to my prediction by saying that the enzyme work best at a pH of 5 and that the opposing pH levels of say 3 and 11 the enzyme reacted insufficiently. From what I predicted about the graph I also believe this to be correct. I predicted that the graph would be of a shape as shown below: [image] Looking at my graph I am adamant that my graph follows this outline, the lines leading up to the optimum pH level and the peak. Evaluation The method I carried out in this experiment I believe gave me sufficient evidence for myself. The evidence I collected, I admit that it would be more reliable if I repeated it again just to make sure the anomalies are based upon the theory of science and not an error occurring due to any wrong doings done by myself in the experiment although I was pleased about the achievements I made in this experiment. If I re-do the experiment considering the errors that may have occurred I believe that my evidence would be correct and could always be relied on. Looking at my graph I realised that there were three anomalous results as pointed out on my graph. These three results are at pH?s 4, 6 and 8. The cause of these results could be many for reasons. The rates per minute at these pH?s did not seem to fit in with the pattern of the rate speeding up towards an optimum pH then decline and becoming denatured. The cause of these anomalies could be that: A major error occurred whilst calculating the mean values of results, which would then mean the whole results being different. Incorrect pH of a solution may have been in the wrong beaker resulting in inaccurate results. Relating to science the cause of the anomalies could be, that at those stated pH?s the solutions are to acidity or alkalinity causing the enzyme to break down and become denatured because with temperature enzymes can be denatured above 45 degrees I think that the same can happen with the pH of a solution because the two factors both effect the rate of enzyme activity. Regarding the quantity of my results I think that what I have obtained is not enough and more precise pHs could have been used such as 5.5,5.6,5.7 then this would ensure me that evidence would be more reliable and prove the optimum pH. Also if further pH?s were used after 9 these could be plotted on the graph to summon up the evidence to draw a firm, sound conclusion on what I have proved. Concerning my method there are a number of alterations or improvements I could have made to obtain more evidence to support my conclusion. As said I could have used further and more precise pHs of solutions. A problem that was encountered whilst doing the experiment was that when the froth would rise it would be a bit difficult to measure how much it had risen because if it overflowed from the measuring cylinder, measuring it was quite a hard procedure and not accurate. To ensure this would not happen I could have used bigger measuring cylinders and in case froth would spill I would cello tape a ruler around the cylinder. Also another problem that occurred was that noting the colour I get from the pH to diminish this problem I could have had sources of information which relate to the pH?s and it?s colours. Although my scientific knowledge enables me to recall the pH?s to their corresponding colours textbook material would have been handy to check that the pH of each solution was correct. The experiment on the whole was a success, but it could be improved by the use of more accurate equipment and with me thinking more logically about minor implications that could occur

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