Q10 = Rate of reaction at (x+10) ºC
Rate of reaction at x ºC
However, enzymes have an optimum temperature for their action.
Change in pH affects the attraction between the substrate and the enzyme. Often, there is an optimum pH, near to pH7. As enzymes normally exist within cells where the pH is 7, the most favorable pH is 7. Some enzymes work better if other substances are also present. Some enzymes, such as pepsin work better if acid is present and some such as lipase are more effective if emulsifying agents are present, this is because they break up the substrate into smaller droplets, this means that there is an increase in surface area, making the enzymes work faster, an increase in concentration also does this because there are more enzymes to work on the substrate. I will look at how temperature affects enzyme activity because it is easier to obtain the correct temperature than it is concentration and pH level. In this experiment every other factor, being pressure, pH and enzyme concentration must be kept the same, so that any changes can only be the result of the temperature change.
Above normal temperatures, heat alters the enzyme molecule irreversibly. This is called denaturing. The denaturing is due to molecular vibrations causes by heat, this changes the shape of the protein, altering the folding and internal cross-linkages in its polypeptide chains.
The substrate becomes unable to fit into the active site and so the enzyme is inactive and will not work even if returned to normal temperatures. The greater the proportion of damaged enzyme molecules the less efficient it becomes. Below normal temperature, enzymes become less and less active, due to the reductions in the speed of the molecular movement. However, this is reversible so the enzymes start to work when returned to the normal temperature.
Aim: To find the effect of temperature on enzymes, using a potato as a catalyst. The source of catalase is in the potato cells.
Preliminary
For my prelim work I set out to find the best concentration that the below experiment would work at. I found that I got good result from 40ml, 3cm of potato and timing for 2 minutes at 40ºC, I used this temperature because I thought that this is when the most oxygen would have been produce and I needed to know whether not too much or too little oxygen would be produced, to be able to measure it. I decided to use these measurements. Here are some of my results from my prelim work:
Apparatus:
- Water Trough
- Burette
- Capillary tube and bung
- 2 Boiling tubes
- 2 beakers
- Stop-clock
- Thermometer
- Bunsen Burner or kettle
- Tripod
- Heatproof mat
- Gauze mat
- Clamp and stand
- Tubing
- Scalpel
- Ruler
- Cutting tile
- Borer
- Boiling tube rack
Set up the following experiment.
Method
Before starting make sure safety glasses are on, hair is tied back and work area is clear, be careful when using the Hydrogen Peroxide, as it is a corrosive chemical, Hydrogen Peroxide is a bleaching agent, so wear a lab coat so it does not bleach clothes, use a tongues to retrieve the boiling tubes from the boiling water baths, be cautious when using sharp scalpels during the experiment to prevent injuries .
More than 1 person is needed for this experiment
- Invert burette full of water in a water trough, after insuring that the tap on the burette is closed.
- Clamp the burette in place
- Attach one end of the tubing to the capillary tube and bung and the other end into the bottom of the inverted burette being careful not to tip the burette or to allow a lot of water into it. If air enters the burette make sure the water is up to a whole number, this will make reading the results more accrete.
- Measure and cut a 3cm piece of potato using the ruler cutting tile and scalpel, make sure that it is exactly 3cm so that the test is fair.
- Measure 40ml³ hydrogen peroxide exactly into a beaker as this would affect the concentration and this is not a variable to be tested.
- Heat a water bath using the Bunsen burner or to save time heat the water using a kettle and add cold water to achieve the correct temperature. Heat two boiling tubes at a time as this will save time.
- Place hydrogen peroxide in to the boiling tube (with thermometer in it) and put in water bath to heat.
- Take the boiling tube out when it has reached the correct temperature, place in a boiling tube rack, put in the potato, then put bung in the end, while somebody else starts the stop-clock.
- Time for 2 minutes
- Read measurements on the burette and pull the bung out.
- Repeat step for another temperature.
Prediction
From my background knowledge I know that as temperature increases, the rate of reaction also increases this is because increasing the temperature makes the particles move faster with more energy, therefore they collide more frequently and powerfully. And so I predict that as the temperature increases so will the enzyme activity, so more oxygen will be produced within two minutes. I think that at around 37ºC the enzyme activity will start to decrease, I believe this will happen because enzymes within the body work better at this temperature and when a human has a temperature enzyme activity starts to decrease. Above 40ºC most mammalian proteins their tertiary and structures are lost; this would result in the loss in ability to catalyse reactions as they become denatured around 60ºC.
Results
Analysis
From the graph, I am able to back up my prediction, I can see when the enzyme is most active and when it starts to denature. From the graph, I have found out that, as the temperature increases, so does the catalase activity, as more oxygen is produce in 2 minutes, up to a certain point (60°C) where the activity has decrease a lot. I found that the optimum for a catalase is at 40°C. This is where the greatest number of collisions takes place between the enzyme and the substrate and therefore the highest rate of reaction is. However my results have not exactly doubled for an increase in 10°C but it is quiet close.
The rate was higher at the higher temperatures (up to 40°C) because as the temperature is raised, so is the energy level of the enzymes and substrate molecules. This means that they have more kinetic energy so they collide more often and therefore more reactions take place between them. This means that the rate increases as more oxygen is produced. The enzyme denatured at about 60°C because the weak bonds, which hold the molecules in shape are broken. The increase in molecular collisions and vibrations at higher temperatures is great enough to permanently change the shape of the active site. The enzyme is denatured because it can no longer form an enzyme-substrate complex as its active site has been permanently changed.
Evaluation
Although I conducted the experiment as accurately as I could there were many errors in the experiment that I used. More than one person is needed to put the potato into the Hydrogen Peroxide and put the bung onto the boiling tube and start the stopwatch all at the same time. Also I think it would have been better if I had used the same potato from the whole experiment as I was unable to due conducting the experiment over a number of days and so I could not use the same potato as they would start to decay. This is a source of error because the concentration of catalase in the potatoes may have been different so the rate of reaction could have been inconsistent. This might be why the enzyme activity at 60°C had not completely stopped. I could repeat the experiment not with three readings at each temperature but also with three different potatoes, this would make the results more accurate. The reading of the temperature may not have been accurate as we could have read thermometer wrong or it could have been a degree over or above without us noticing, so this could have affected my results
There could also have been a slight variation in the length of the potato because it was very difficult to get them all exactly 3 cm even though I was using a ruler and scalpel. Next time I would use shorted pieces of potato and could weight them so that it would know that they are the same length. I would use less hydrogen peroxide as the amount I used was probably unnecessary and would have work with a smaller amount. If I was to repeat this experiment I would also take more readings, every 5°C instead of every 10°C because if I did this I would be able to plot a more accurate graph and it would be easier and more accurate to tell when the enzyme got to the optimum and denaturing temperatures.
I think that I obtain a good range of results even though I could have got more. My results are good enough to support my prediction and I have met my aim to find the effect of temperature on enzymes, using a potato as a catalyst.
