Lock and Key Mechanism
Emil Fischer suggested the lock and key theory in 1894, and described it as: "The specificity of an enzyme for its substrate arises from their geometrically complementary shapes".
The lock and key theory is a simple way of explaining that each enzyme is specific to breaking down its substrate. It is called a lock and key theory because it is like a lock, which needs a specifically shaped key in order for it to work. Part of the structure of an enzyme contains the active site. This is which the enzyme can attach to the substrate so that it can perform some chemical reaction.
When the milk and the enzyme are heated up to a high temperature the enzyme will perform good until it reaches its optimum temperature were it would perform the best. But as this temperature exceeds the optimum temperature the enzyme will not react as fast with the substrate. This is because the active cell of the enzyme becomes denatured so it will not be able to break down the substrate using the lock and key method. Because the active site becomes denatured the substrate and the enzyme cannot become locked together so the substrate cannot become broken down.
The following are important factors, which affect enzyme activity:
- Enzyme concentration
- Substrate concentration
- Ionic concentration
- Water activity
- Temperature
Preliminary work:
I carried out an experiment to find out if the concentration of enzyme affects its reaction time. To do this experiment I made a colour standard by adding hydrochloric acid to milk. The colour of this solution was clear because all the protein in the milk has been digested. Next I added different amounts of the enzyme trypsin, to 5ml of milk. I measured the time it took for the substance to change to the same colour as the colour standard. After doing the experiment I found out that when we added a higher concentration of enzymes to the substrate it got broken down a lot faster. This can be explained by using the collision theory.
In chemical reactions the atoms in elements or compounds are separated and recombined in new arrangements. For this to happen the atoms have to collide with enough energy for bonds to be broken before new ones can be formed. We change the rate of reaction by changing the number of effective collisions per second.
Lots of things can affect the amount of collisions like: surface area, concentration and temperature.
In our preliminary experiment the amount of collisions were made to increase by the increase of the amount of enzymes so the time to break down the substrate was reduced.
Apparatus:
Milk 0.04%
Trypsin 0.5%
10cm3 of Hydrochloric acid
5cm3 water
Beaker
Stop clock
Measuring cylinders
Test tubes
Pipettes
Water Bath
Method:
First I will add 5cm3 of milk and 5cm3 of distilled water in to a test-tube using appropriate apparatus. This will be used as a colour standard, which will be used in comparing the reactions taking place.
Next I will and 5cm3 of hydrochloric acid to a test tube, which will also contain 5cm3 milk. The colour of the substance in the test tube should be translucent because the milk has been completely digested.
Next I will add 5cm3 of milk to 5cm3 of milk and start the top watch. I am measuring this in room temperature, which was 20 degrees. I will measure the time taken until the colour of the test tube matches the colour of the second colour standard.
Then I will set up the water bathes to measure the required temperatures (10, 20, 30…). I will then do the same as before but I will place the test tubes in the water-bathes and use a stopwatch to measure the time taken for the substance to match the same colour as the colour standard.
I will repeat this for the other different temperatures.
Diagram:
Safety:
To make sure my experiment is safe I will wear safety goggles to protect my eyes against the hydrochloric acid. Also during the experiment I will use different pipettes for each substance so there will be no risk of contamination.
Fair Test:
I will make the test fair by measuring each temperature three times to make sure my results are accurate.
Also I will make sure I add the same amount of milk and enzyme in each of the test tubes. Also I will make sure I read the time accurately and at the right time. So there will not be a lot of human errors during the experiment.
Results:
The experiment was repeated three times for each temperature
