AIM: The effect of substrate concentration on the activity of catalyse
PREDICTION:
I predict that, as substrate concentration increases, initially the rate of reaction will also increase. However after a certain point the catalyse stops having the ability of working any faster. Thereafter after this point the rate of reaction cannot increase any further.
Enzymes are protein molecules, which can be defined as biological catalysts. A catalyst is a molecule, which speeds up a chemical reaction, but remains unchanged at the end of the reaction. (Jones, 2000: 43)
There are two types of possible catalyst reactions that can occur:
- A reaction in which a larger molecule is broken down into a smaller molecule.
Fig 1.1: In this experiment I will be monitoring this reaction, which shows the break up a large molecule, hydrogen peroxide, to form smaller molecules, water and oxygen.
The graph below shows that as substrate concentration increases the rate of reaction also increase up till a certain point known as V-max. This is how I expect my graph to look like after the experiment.
Fig 1.2: (Williams, 2000: 70)
The human body produces this catalyse in cells to prevent the accumulation of hydrogen peroxide, a substance that is toxic and a waste product in cells.
- A reaction in which smaller molecules combine to form a larger molecule.
Fig 1.3: The formation of a dipeptide molecule from two amino acids. (Williams, 2000: 63)
This reaction involves the break down of hydrogen peroxide, H O , into water and oxygen. Potatoes will be used as a source of catalyse.
These biological catalysts are known as globular proteins (amino acids). The name comes hence from its spherical and globular structure. These globular structures can also be defined as having a tertiary structure. This is as a result of the three types of bonds holding the catalyst together.
Hydrogen bonds: These form between the R groups and are relatively weak. If I increase the substrate concentration this would lead to an increase in collisions therefore more enzyme-substrate complexes would be formed up to a point.
Ionic bonds: These occur between ions and are also much more stronger than the hydrogen bonds. However these ionic bonds are broken by temperature and pH changes.
Disulphide bonds: These are the strongest types of bonds. They occur between the sulphur atoms. The hydrophobic effect allows for the globular proteins to maintain their structure. The hydrophobic groups point inwards and the hydrophilic groups point outwards.
Fig 2: Part of a globular molecule (Williams, 2000: 21)
Enzymes (catalysts) have certain properties that allow them to function in the way in which they do:
- They are specific
- They never get used up
- Enzymes react with the substrate to form enzyme-substrate complexes
- Enzymes only work if a co-factor is available
- Catalysed reactions are stopped by the presence of inhibitors
- The rate of reaction is affected by pH and concentration
Induced fit theory: This idea is used to explain why enzymes are specific. The active site of the catalyst is the region where the catalyst and the enzyme join; in this case the substrate does not fit the active site exactly. The active site moulds into the shape of the substrate. After the reaction the catalyst returns to its original form.
Fig 3.1 Above shows how the induced fit theory works.
Activation energy: In this investigation I will be changing, lowering, the activation energy by changing the substrate concentration. The potatoes will act as a source of substrate. In turn I will have to ensure that the other variables are kept constant to make sure that this experiment is conducted fairly.
I will be changing the substrate concentration. The amount of enzyme will stay the same, however the rate of reaction would increase up till a point.
Fig 4.1: The graph produced when the activation energy is lowered. (Williams, 2000: 67)
