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Investigation of how different concentration of enzyme catalase affects the rate of breaking down substrate hydrogen peroxide

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Investigation of how different concentration of enzyme catalase affects the rate of breaking down substrate hydrogen peroxide Introduction Enzymes are large proteins that speed up chemical reaction. As globular protein, enzymes have a specific three-dimensional shape which is determined by their sequence of amino acids. Despite their large overall size, enzyme molecules only have a small region that is functional. This is known as enzyme's active site. The substrate molecule is held within the active site by bonds that temporarily form between the R groups of the amino acids of the active site by bonds and all groups on the substrate molecules. This structure is known as enzyme-substrate complex. Enzymes are classified into several categories, such as hydrolytic, oxidising, and educing. Depending on the types of reaction they control. In this case, the enzyme I will use in the investigation is catalase from celery extract, which is concluding as hydrolytic enzyme. This type of enzyme accelerates reactions in which a substrate is broken down into simpler compounds through reaction with adding up water molecules. Oxidising enzyme, known as oxidises, accelerate oxidation reaction; reducing enzyme speed up reducing reactions in which oxygen is removed. A substrate is the molecule, which can bind into the active of enzyme. In this case, I will use hydrogen peroxide as the substrate. Enzyme works in the same way as a key operates a lock. Enzymes' active sites have a particular shape like a lock and only a particular key ( substrate) can fit into that lock. Enzymes are therefore specific in the reactions that they catalyse. This is known as the 'lock and key theory'. In practice, unlike a rigid lock, the enzyme actually changes its form slightly to fit the shape of the substrate. In other works, it is flexible and moulds itself around the substrate. As it alters its shape, the enzyme puts a strain on the substrate molecule and thereby lowers its activation energy. ...read more.


Preliminary work In order to get finest and reliable results, I did a preliminary work. This enable me not just find out a suitable range of celery extract of catalase concentration I will use in my real experiment, but also help me descried the time interval I will measure the oxygen get and justify the equipment and method. I think these all lead me to get reliable and accurate results in the end. In the preliminary work, I choose to do three different concentration of celery extract. To get different concentrations of celery extract, I used distilled water to dilute the celery extract. I tested the range of celery extract between 100% --20%, the highest concentration is 100%, the lowest concentration is 20% and the median is 60%. The reason I chose these three concentrations is because between each concentration, there is 40% difference and this enable me to test that in which level of concentration, reaction goes best and to find out which concentration of celery extract I will use in my real experiment. The concentration of celery extract I used as following table: Concentration of catalase / % Volume of celery extract / cm3 Volume of distilled water / cm3 20% 2 cm3 8 cm3 60% 6 cm3 4 cm3 100% 10 cm3 2 cm3 I used 15 cm3 of hydrogen peroxide for each concentration of celery extract, therefore the concentration of substrate will not affect the rate of reaction. The results of preliminary work as following: Time/s Total volume of oxygen gas collected at different concentration of celery extract / cm3 20% 60% 100% 10 0.7 3.2 4.5 20 1.1 4.9 18.5 30 1.4 6.0 24.5 40 1.6 7.0 30.5 50 1.8 7.7 32.5 60 2.0 8.6 35.5 70 2.2 9.2 37.3 80 2.4 9.8 40.7 90 2.6 10.5 42.7 100 2.8 11.6 44.8 110 3.0 11.8 120 3.2 12.2 130 3.4 12.6 140 3.6 13.1 150 3.8 13.4 160 4.0 13.9 170 4.2 14.3 180 4.4 14.6 From my preliminary ...read more.


6.0 cm3 55% 5.5 cm3 5.5 cm3 70% 7.0 cm3 3.0 cm3 85% 8.5 cm3 1.5 cm3 100% 10.0 cm3 0.0 cm3 2. set up equipments as diagram. ( making sure there are no bubbles inside the gas tube) 3. using 20ml syringe to measure 20 cm3 of hydrogen peroxide and transferring it to the conical flask which has contain 25% of celery extract, make sure that the bottom of thistle funnel is below the liquid level. 4. once inject the hydrogen peroxide into the thistle funnel, put the delivery tube under the gas tube after few seconds and start the stopwatch immediately. 5. read and write down the volume of oxygen gas every 10s for up to 3 mins. 6. repeat step 3 to 5 for catalase concentration of 40%, 55%, 70%, 85% and 100%. 7. redo this experiment 3 times for each concentration of catalase. 8. calculate the average volume of oxygen and plot a graph. Method justifications I chose to use different concentrations of celery extract therefore I can get different concentration of enzyme catalase concentration. This enable me to investigate how different concentration of catalyse affect the rate of breeding down hydrogen peroxide. I will use 6 concentrations in order to plot a graph minimum of 5 points. At step 4, the delivery tube is put under the gas tube after few seconds when hydrogen peroxide inject into the conical flask. This because the first few bubbles may come from the air in the delivery tube and are pressed out by the pressure. After few seconds to put the tube can avoid the fist few bubbles from the air. The repeating lead me to get 3 volume of oxygen in each 10s, this enable me to see if is the result reliable. If the results are very similar, I can conclude that the are reliable; if it is not, perhaps the method is not good.( e.g. the delivery tube to gas tube may lose some bubbles when starting the stopwatch) ...read more.

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