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Investigation of Enzyme Activity

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An Investigation of Enzyme Activity with different Substrate Concentrations. Aim To investigate how different concentrations of substrate affects the rate of enzyme activity. Objective My objective is to determine how different concentrations of substrate, affects the rate of enzyme activity. I will do this by using different concentrations of Hydrogen Peroxide, and mixing it with the enzyme catalyse. Then I will measure how much gas is produced. Theory What is an Enzyme? Enzymes are proteins which are biological catalysts. A catalyst in chemical terms substantially reduces the energy barrier which exists between atoms and which prevents the atoms from getting close enough to react and form a bond with one another. An enzyme lowers the energy of activation of a reaction but the catalyst is not changed in any way in the process .Therefore, when the atoms of molecules are acted upon by enzymes, an identical reaction occurs as would have occurred without the enzyme but, the energy hill required to overcome the getting-close barrier, is much, much smaller than would have been true without the enzyme's help. The structure of the enzyme is such that atoms of molecules can get close enough to interact, but the energy required to allow this closeness is relatively small. ...read more.


The substrate can no longer bind, and the reaction is no longer catalysed. At very high temperatures this is irreversible. Only the weak hydrogen bonds are broken at these mild temperatures; to break strong covalent bonds you need to boil in concentrated acid for many hours. 2. pH Enzymes have an optimum pH at which they work fastest. The pH affects the charge of the amino acids at the active site, so the properties of the active site change and the substrate can no longer bind. Table II pH for Optimum Activity Enzyme pH Optimum Lipase (pancreas) 8.0 Lipase (stomach) 4.0 - 5.0 Lipase (castor oil) 4.7 Pepsin 1.5 - 1.6 Trypsin 7.8 - 8.7 Urease 7.0 Invertase 4.5 Maltase 6.1 - 6.8 Amylase (pancreas) 6.7 - 7.0 Amylase (malt) 4.6 - 5.2 Catalase 7.0 3. Enzyme concentration As the enzyme concentration increases the rate of the reaction increases linearly, because there are more enzyme molecules available to catalyse the reaction. At very high enzyme concentration the substrate concentration may become rate-limiting, so the rate stops increasing. Normally enzymes are present in cells in rather low concentrations. 4. Substrate concentration The rate of an enzyme-catalysed reaction shows a curved dependence on substrate concentration. ...read more.


I say this because of my theory. As the substrate concentration increases, the rate increases because more substrate molecules can collide with enzyme molecules, so more reactions will take place. However I predict that the enzyme will be a limiting factor after a certain concentration, and therefore the fate of reaction will not go any faster. This is because there are no more available active sites to increase the rate of reaction. . At higher concentrations the enzyme molecules become saturated with substrate, so there are few free enzyme molecules, so adding more substrate doesn't make much difference I believe my graph will look like this because of my prediction. Equipment 8 Test Tubes with Bungs with holes in them 20 mls of 0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, 3.2 Mol/dm3 Test Tube Rack Distilled Water 100ml Gas Syringe Stop Clock 100 mls of Catalyse Pipette Method 1. Using the Pipette, put 5mls of Catalyse into each of the 8 test tubes. 2. Then put 5mls of Hydrogen Peroxide at 0.4 Mol/dm3 into the first test tube. 3. Then quickly attach the 100ml Gas Syringe to the test tube. 4. Collect gas produced for 5 minutes. Use the stop clock to time your experiment. 5. Record your results, and then repeat the procedure. 6. Then repeat the whole procedure, this time for a different concentration of Hydrogen Peroxide. ?? ?? ?? ?? 1 ...read more.

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This is a very in depth and detailed account of the biochemistry of enzymes. It is written in a clear and logical manner and contains advanced theorys.

Marked by teacher Brady Smith 17/07/2012

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