The enzyme catalase speeds up the decomposition of Hydrogen Peroxide into water and oxygen as shown here, 2H2O2——————-*2H2O+O2.
It is one of the fastest known enzymes and its turnover number is 6 million, which means the number of substrate molecules which one molecule of the enzyme turns to products per minute. This can be demonstrated by putting a piece of liver into a beaker of Hydrogen Peroxide, the fizzing shows a demonstration of the enzyme in action.
My aim is to examine how the concentration of the substrate hydrogen peroxide affects the enzyme catalase.
I am going to investigate the effect of varying the substrate concentration on enzyme catalase. I am going to use 8 different concentrations and record the time taken to collect 20ml of gas in the gas syringe. I will repeat all the 8 concentrations twice so I can see if they match, spot out any anonymous results and also I can work out the average time it takes to produce 20ml of gas at the certain concentrations. I will vary the concentrations by increasing and decreasing the amounts of Hydrogen Peroxide and water.
First of all I will ensure I have enough enzyme solution for the whole experiments so the enzyme solution is standardised. With the results I get I will try to work out the Vmax. I will do this experiment at room temperature so the enzymes get enough kinetic energy to collide. I will need 80ml of the enzyme solution because I will use 5ml for all of the experiment and I will do 8 different concentrations and I will repeat this concentrations twice so that is 5x8x2= 80. First of all I will set out the equipment as I will show in the diagram then I will cut some pieces of liver, which is the source of the enzyme. Then I will grind the pieces of liver with the mortar and pestle, which will have sand and Di ionised water (which is water with no H ions in it its PH is neutral). The sand will help cut open the cells of the liver. I will take a funnel with glass wool in it, I chose glass wool rather than filter paper because the catalase could have been adsorbed by the filter paper. Then I will add 5ml of the enzyme catalase to the conical flask and for the substrate concentration of 10% I will add 2ml of Hydrogen Peroxide and 18ml of water (18+2= 20, I will always use 20ml) every time I when I will increase the concentration by 10% I will increase the H2O2 by 2ml and decrease the H2O by 2ml. I will time how long it takes to produce 20ml of gas in the gas syringe. I chose the gas syringe rather than to count the bubbles produced in a measuring cylinder because it is easier to use, the results will be more accurate and the gas syringe reduces the possibility of gas escape. I will tabulate my results and highlight them in some way so they are visible I will interpret my results in to a line graph. I will also added a line of best fit to the results on the graph and with the results I get I will work out the Vmax.
Here is a blank copy of my results table, which I fill in later when I get my results.
To make my experiment a fair test I need to ensure that all the variables must be kept the same for all the experiments except for the concentration of Hydrogen Peroxide.
I will accurately measure out the Hydrogen Peroxide and enzyme solution using a pipette and measuring cylinder. I will use glass wool rather than filter paper because if I use filter paper then the catalase could be adsorbed by the filter paper, which will no longer make my experiment a fair test. I will time how long it takes to produce 20ml of gas by using a stopwatch accurately. For each concentration I will make sure that there is no excess catalase or substrate in the measuring cylinders I use by cleaning them. I will hold the rubber bung connecting the conical flask and the gas syringe so it does not open and let out any gas.
I predict that the more the concentration of substrate the faster it will be to produce 20ml of oxygen if you increase the concentration there will be a higher chance of collision between the particles, but there will come a point where all the active sites are full and the rate should go constant. Enzymes such as catalase are protein molecules. They are used to speed up specific reactions in the cells. They are all very specific as each enzyme just performs one particular reaction. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. The graph should look like this,
I know this from background scientific knowledge, from my notes and textbooks.
The safety precautions that I will consider taking are that I am going to ensure that I wear goggles because Hydrogen is a strong oxidising agent and if it gets into my eyes it could be irritating and eat away at my cornea, corneal burns can occur rapidly. I will also make sure that the Hydrogen Peroxide does not come in contact with my clothes or hands so I will wear an apron and gloves if the Hydrogen Peroxide does come in contact with my hands, which will cause whitening of the skin and stinging. I will immediately wash my hands thoroughly with water. Hydrogen Peroxide is a strong deodorizing and bleaching agent. It has a characteristic pungent odor. If anyhow I swallow the Hydrogen Peroxide I will drink water straight away to dilute and immediately contact a physician.
If I break any apparatus I will inform the teacher straight away and I will clean the broken apparatus.
? Scalpel and chopping board
? 4 measuring cylinders, (3) 100ml (1) 10ml
? Conical flask
? Gas syringe
? Mortar and pestle
? Glass wool
? Rubber bung with delivery tube
? Retort stand with clamp and boss
? Hydrogen Peroxide
? Di ionised water
? Source of enzyme (liver)
I used these apparatus because it was the equipment available and suitable for my experiment. I used the gas syringe rather than to count the number bubbles produced in a measuring cylinder because it is more easier and accurate and it also gives a less possibility of gas escape. I used the stopwatch because it is accurate to measure the time rather than counting the time yourself. I used the spatula to pick up bits of the sand and put in the mortar and pestle in which I was grinding the pieces of liver. I used the scalpel to cut the pieces of the liver and I cut the pieces on the chopping board so I dont cut into the table that I was working on. I used the mortar and pestle to grind the pieces of liver. I used the glass wool rather than filter paper because the catalase could be adsorbed by the filter paper, which will no longer be a fair test.
First of all I ensured I had enough enzyme solution for the whole experiments so the enzyme solution was standardised, so if incase I am in between an experiment and the enzyme solution finishes then if you make the solution again you might not get the right concentration, so the experiment will not be a fair test. I used pipettes to get the solutions and I accurately measured the amounts by using measuring cylinders. I needed 80ml of the enzyme solution because I used 5ml for all of the experiment and I done 8 different concentrations and I repeated these concentrations twice so that is 5x8x2= 80. First of all I set up the equipment as shown in the diagram then I cut some pieces of liver, which was the source of the enzyme. Then I grinded the pieces of liver with the mortar and pestle, which had sand in it and Di ionised water (which is water with no H ions init its PH is neutral). The sand helps cut open the cells of the liver. I then took a funnel with glass wool in it, I chose glass wool rather than filter paper because the catalase could have been adsorbed by the filter paper. Then I added 5ml of the enzyme catalase to the conical flask and for the substrate concentration of 10% I added 2ml of Hydrogen Peroxide and 18ml of water (18+2= 20, I always used 20ml) every time I increased the concentration by 10% I increased the H2O2 by 2ml and decreased the H2O by 2ml.
A problem did occur at one point when I was doing my experiment for TRIAL 1 for the substrate concentration of 30%, it took a long time, much longer to get to 20ml of gas produced its time was no where near the previous concentration it had no pattern, so I stopped it and I repeated it again then it was alright it took normal time it was in pattern with the other concentrations. Probably the reason for the reaction at that particular concentration to take that long when I did it first might have been that the enzyme must of deteriated fast or when I put the enzyme in the conical flask with the substrate and put the rubber bung on top I might of took a little while to time the reaction, but then I repeated it again and it was alright.
I timed how long it took to produce 20ml of gas in the gas syringe. I chose the gas syringe rather than to count the bubbles produced in a measuring cylinder because it is easier to use, the results will be more accurate and the gas syringe reduces the possibility of gas escape.
I tabulated my results and highlighted them in some way so that they were visible I interpreted my results in to a line graph. I also added a line of best fit to the results on the graph.
I used substrate concentrations from 10%–80% I varied the concentrations by increasing and decreasing the amounts of Hydrogen Peroxide and water for example for the substrate concentration of 10% I used 2ml of Hydrogen Peroxide and 18ml of water, for the substrate concentration of 50% I used 10ml of Hydrogen Peroxide and 10ml of water, etc. I used pipettes to get the solutions and I accurately measured the amounts using measuring cylinders. I used a gas syringe to collect the volume of gas produced. I timed how long it took to produce 20ml of oxygen using a stopwatch. To work out the average time taken (in seconds) to produce 20ml of oxygen at different concentrations, I collected the time taken for TRIAL 1 and TRIAL 2 in minutes and seconds and then divided the results for each concentration by 2 then the final results was converted into seconds. I tabulated the results, highlighted them and interpreted them on to a graph with a line of best fit on the graph.
Here are my results of the 8 different concentrations repeated twice and a graph to interpret them.
My results show that the increase of concentration of the substrate, which was Hydrogen Peroxide, increased the speed of the time taken to produce 20ml of oxygen. My results do not support my prediction. My results do not fully go with my prediction which was that the more the concentration of substrate the faster it will be to produce 20ml of oxygen if you increase the concentration there will be a higher chance of collision between the particles, my results show the explanation of the theory of kinetic energy, but there will come a point where all the active sites are full and the rate should go constant, but my results did not show that. I knew that the prediction was true because of scientific background knowledge, from my notes and from science textbooks.
I could not work out the Vmax because my results are not reliable and there could be lots of possibilities that effected my results such as, I should have repeated the 8 different concentrations more than twice, which will give me more results to compare, the temperature in the room could have changed by a degree or two which could have altered my results, there might have been the possibility of gas escape between the rubber bung and the gas syringe which was connected via a delivery tube, there is a slight delay between pouring the Hydrogen Peroxide into the conical flask, adding the catalase, putting the bung on and starting the stopwatch, which could give a different result. I should have got someone else to start and stop the stopwatch, which is not possible if no one wants to do that. I may have measured the concentrations inaccurately, which could have altered my results.
Looking back at my experiment, the changes I could have made to improve and benefit it could have been, that I could have repeated the 8 different concentrations more than twice, which will give me more results to compare BUT there was a time limitation. I could have used better apparatus which would have made my experiments more fair and efficient, but that depends on the availability of equipment and better apparatus are more expensive and larger and which make them harder to handle and less safe to work with because of size and the apparatus could be new to me and I could mishandle it. I think the apparatus I had was the probably the best available. I could have tested different sources of the enzyme catalase e.g. apple, peas, etc. But that is time consuming, and again there was a time limitation. The obtaining of the enzyme was quite time consuming, my enzyme source was pieces of liver which I had to firstly cut using a scalpel, grind with a mortar and pestle with some sand and Di ionised water which wasted time, probably there could have been an easier way to obtain it, which would have saved me time, may be to repeat my experiment again.
The hydrolysis of milk fats by lipase
Lipase is a digestive enzyme produced in the pancreas. It flows into the small intestine where it breaks down fats to fatty acids and glycerol. In this experiment you will investigate the relative concentrations of lipids in three types of milk:
? full fat
The concentration of the lipids in the samples can be assessed by adding lipase to the milk.
Lipase is a digestive enzyme produced in the pancreas. It flows into the small intestine where it is responsible for the hydrolysis of triglycerides to fatty acids and glycerol.
It is possible to follow the reaction by monitoring the pH of a mixture of milk, lipase and sodium carbonate. A milk with higher lipid content should release a greater number of fatty acids in a given time period and therefore its pH should drop quickest.
1. Place 10ml fresh milk in a boiling tube (1) and add 5ml of dilute (0.05M) sodium carbonate solution. Place the boiling tube in the water bath to warm to 40C for 5mins.
2. Place 1ml of 5% lipase in a boiling tube (2) and place in the water bath to warm to 40C for 5mins.
3. Set up the datalogging equipment as shown below.
4. Pour the milk with carbonate solution into the warmed enzyme . Shake the boiling tube and return to water bath.
5. Record the change in pH for 8 minutes.
6. Rinse the pH probe in the pH7 buffer solution and repeat experiment with a different milk sample.
Bile salts are steroids with detergent properties which are used to emulsify lipids in foodstuff passing through the intestine to enable fat digestion and absorption through the intestinal wall. They are secreted from the liver stored in the gall bladder and passed through the bile duct into the intestine when food is passing through.
Biosynthesis represents the major metabolic fate of cholesterol, accounting for more than half of the 800mg/day of cholesterol that the average adult uses up in metabolic processes. By comparison, steroid hormone biosynthesis consumes only about 50 mg of cholesterol per day. Much more that 400 mg of bile salts is required and secreted into the intestine per day, and this is achieved by re-cycling the bile salts.
Most of the bile salts secreted into the upper region of the small intestine are absorbed along with the dietary lipids that they emulsified at the lower end of the small intestine. They are separated from the dietary lipid and returned to the liver for re-use. Re-cycling thus enables 20-30g of bile salts to be secreted into the small intestine each day.
The most abundant of the bile salts in humans are cholate and deoxycholate, and they are normally conjugated with either glycine or taurine to give glycocholate or taurocholate respectively. The conjugation is important in identifying the bile salt for re-cycling back to the liver.