Temperature can alter the active site at high temperatures as it changes the shape of the enzyme and destroys the active site. This means the substrate can no longer be catalysed and therefore the rate of reaction decreases. Up until the temperature denatures the enzyme, every 10ºc increase in temperature doubles the rate of reaction. Cooling the enzyme will inactivate the enzyme, but doesn’t denature it and therefore is able to work again when it is heated up.
PH also affects the rate of reaction. Small changes in pH can change the rate of reaction without denaturing the enzyme, but at the extremes of pH the enzyme can become unstable and denatured. Free hydrogen or Hydroxyl ions can affect the charges on the amino acid side chains of the enzymes active site. This affects the hydrogen bonding and so changes the 3-D shape of the enzyme and the shape of the active site. The substrate no longer fits the active site and so is unable to be catalysed by the enzyme. Another situation that can arise from extreme pHs is the active site can become flooded with hydrogen or hydroxyl ions and this can prevent the substrate from fitting the active site. Low pH means there are too many hydrogen ions. This prevents the active site and the substrate binding as they both become positively charged and repel each other. High pH has a similar effect, but has an increase in Hydroxyl ions and this means both become negatively charged at repel each other.
Some enzymes require cofactors before they can catalyse the reaction. Cofactors are non-protein molecules, which modify the chemical structure of the enzyme so it can function more effectively.
Inhibitors:
Inhibitors are substances that decrease the rate of reaction. This is achieved by the inhibitor binding with the enzyme and preventing it from forming and enzyme-substrate complex. Inhibitors can either be reversible or non-reversible. If an inhibitor is reversible the effect is only temporary and can be reversed when the inhibitor is removed. There are two types of reversible inhibitor; the competitive inhibitor and the non-competitive inhibitor.
The competitive inhibitor has a similar structure to the substrate and is therefore able to bind with the active site. This decreases the number of active sites available to bind with the substrate, there fore decreasing the rate of reaction. Increasing the substrate concentration can decrease the effect of the inhibitor, as there is more substrate to compete for the active sites.
The non-competitive inhibitor attaches to another part of the enzyme and its presence alters the overall structure of the enzyme, including the active site, therefore preventing the enzyme-substrate complex being formed. As there is no actual competition for the active site, increasing the concentration will have no effect on the rate of reaction.
Non-reversible inhibitors alter the enzyme permanently; this is due to the inhibitor affecting the disulphide bonds holding the enzyme together. This alters the tertiary structure of the enzyme causing I to lose its catalytic properties.
In the experiment I am going to conduct I am going to be researching the effect of the concentration of the inhibitor CuSO4 has on the decomposition of H2O2 by the enzyme catalase. To perform this experiment I will first need to perform a preliminary experiment, as I know that catalase is present in root vegetables, but I need to find out which root vegetable contains the highest levels of catalase, and therefore the best catalyst for To find a root vegetable that catalyses the break down of hydrogen peroxide in to water and hydrogen gas to the best ability.
Preliminary investigation to find the best available catalyst.
Aim: To find to the root vegetable that contains the highest level of the enzyme Catalase using the decomposition of hydrogen peroxide.
Variables: I will maintain the temperature, the volume of hydrogen peroxide and the surface area of the vegetable samples. However I will alter the type of vegetable.
Apparatus:
Potato
Carrot
Swede
Parsnip
Hydrogen peroxide 20 Vol
Conical flask
Rubber bung
Tubing
Apple Corer
Ruler
Water bath
Gas syringe
Thermometer
Method:
- Use an apple corer and ruler to cut equal lengths of each vegetable
- Place each sample into a conical flask and label them
- Add 20 cm3 of hydrogen peroxide to the first conical flask and attach the gas syringe using tubing and a rubber bung.
- Measure the volume of gas given off and record the volume.
- Repeat with other 5 samples.
Results:
Errors:
- The pipettes used to measure the volume of Hydrogen peroxide has an error of 0.05ml
- The ruler used to measure the length of the potato has an error of 0.5mm. This is 0.5mm3 as the potato is a cylinder.
- The gas syringe has an error of 5cm3
- The thermometer has an error of 0.05ºc.
When these errors are taken into consideration, the overall error is 5.1cm3.
These results show that potato contains the highest level of the enzyme Catalase as potato gave off the highest volume of gas in a fixed amount of time, which tells me the rate of reaction is highest with potato as the catalyst. The potato is a catalyst because it naturally contains the enzyme Catalase. Therefore in my investigation to find the effects of different concen trations of the inhibitor copper sulphate I will use potato as the catalyst.
