When Hydrogen Peroxide is broken down there are two products, Oxygen and water. However, the breakdown of Hydrogen Peroxide requires the enzyme catalase which catalyses the reaction. Catalase is found in microbodies and in this experiment the source of catalase is yeast. The formula for the decomposition of Hydrogen peroxide is: (Catalase) H2O –> H2O + O2 The reaction is an anaerobic one, meaning it happens in the absence of oxygen. To measure the rate of the enzyme reaction I will collect the oxygen produced in the reaction over a two-minute period. Also, I will vary the concentration of the hydrogen peroxide each time.
So my experiment will look at how the concentration of H2O2 affects the speed of an enzyme controlled reaction. Enzymes, such as catalase, are used to speed up a specific reaction. Each enzyme has an active site in which the break down of the substrate occurs. However, each enzyme’s active site is shaped to fit one type of substrate and is said to be specific to the substrate. The specificity of an enzyme to its substrate is known as the ‘Lock and Key’ theory. Enzymes are globular proteins made up of amino acids and s in any globular protein; there are four types of bonding that give the protein its three-dimensional structure.
The four types of bond are disulphide bond, hydrogen bond, ionic bond and hydrophobic interactions. When it has been shaped the amino acids that make up the enzyme’s active site and called catalytic amino acids. The aim of this investigation is to find out how substrate concentration will affect the initial rate of reaction. Substrate concentration is an independent variable while the rate of reaction is a dependent variable. An independent variable is a variable that the values have already been chosen for, while the dependent variable is the result or measurement taken that would relies upon the value of the independent variable.
“For a given amount of enzyme, the rate of an enzyme-controlled reaction increases with increasing substrate concentration” (Glenn and Susan Toole, 1999). If there is a low substrate concentration then there is not enough substrate to bind with the enzyme. “However, if the substrate concentration continues to increase, with a constant enzyme concentration, there comes a point where every enzyme’s active site is forming enzyme-substrate complexes at its maximum rate.
If more substrate is added, the enzyme simply cannot bind with the substrate any faster; substrate molecules are effectively queuing up for an active site” (Indge, Rowland, Baker, 2000). “Each type of enzyme will usually act on one type of substrate molecule. This is because the shape of the active site will only allow one shape of molecule to fit. This enzyme is said to be specific to this substrate” (Jones, Fosbery, Taylor 2000). The idea that a substrate fits into the active site of an enzyme is called the ‘lock and key’ theory.
As there is no inhibitor present I can presume that there will be nothing to obstruct the enzymes active site, as inhibitors, whether permanent or temporary, can slow a reaction down by binding to an enzymes active site and blocking the substrate. For my results I would expect to see the initial rate of reaction increasing as the substrate concentration increases. At some stage on the graphs of my results the best-fit line will become constant, as this is the time where all of the active sites are working at their maximum, known as Vmax and therefore the reaction is going as quickly as it can.
Key Variable Type of Variable If control variable, how will it be controlled? Effect of variable on investigation. Substrate Concentration Control I will make solutions of 5 different concentrations using water to dilute the H202. – Temperature Independent – The higher the temperature is the faster the enzyme and substrate move. This means that there will be more collisions, meaning the reaction will happen quicker as the chances of the active site and the substrate colliding is increased. At lower temperatures the collisions are fewer, so the reaction is slower.
If the temperature is too high then the enzyme will denature. This means that the active site will be damaged, and will no longer fit with the substrate. This means that no reaction will occur. pH Independent – If the pH is very different to an enzymes optimum pH then the enzyme can be denatured as the hydrogen ions (of which pH is a measure) can interact with the amino acid R groups and affect the way they bond with each other. Enzyme Concentration Independent – Enzyme concentration causes there to be a fast initial rate of reaction as there are lots of free active sites for the substrate to collide with.
It is unlikely, with a higher concentration of enzyme than substrate, that the substrate will be queuing, and this means that the reaction will happen faster. If the concentration of the enzyme is lower than that of the substrate then the reaction will be slower as the enzyme will be working at Vmax and the substrate will be queuing. Inhibitors Independent – Inhibitors slow down or stop a reaction from happening. Competitive inhibitors compete with the substrate for the enzyme’s active site. These slow reactions down.
If it is reversible it means that if the substrate concentration is increased then there will be less inhibition, speeding the reaction up. If the inhibition is non-competitive irreversible then the inhibitor will bind to the enzyme’s active site and remain there, even if substrate concentration is increased. This will prevent a reaction from occurring. Sometimes the inhibitor will bind to the enzyme but not with the active site. This is seen as non-competitive inhibition and while bonded no reaction can occur. Initial Rate of Reaction Dependant – – Below are the results from my pre-test.
O2 Collected (cm3) Amount of H2O2 (ml) Amount of Water (ml) These results show that as the concentration of H2O2 increased, the amount of O2 collected increased. This means that my prediction is most likely to be correct although there is a chance that the results above are anomalous as the results were only taken once and not three times like they will be in the actual test.