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Enzyme Specificity

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21/11/02 Enzyme Specificity Dora Winstone F26 Enzymes are specific and usually only attack one bond in the substrate, and then join to the active site. This experiment investigates the specificity of enzymes, which part in a variety of similar substrates, the enzyme will bind to. This experiment uses fermentation with yeast to test this. Glucose is the only sugar that is used in respiration so by testing a group of similar monosaccharides along with glucose, the part of the sugar that is used can be defined. All of the sugars used in this experiment are monosaccharides, which means some have the same formula as glucose but not the same structure. Fermentation in this experiment uses anaerobic respiration, without oxygen. This is the reaction for anaerobic respiration : Sugar ethanol + carbon dioxide + energy C6H12O6 2C2H5OH + 2CO2 + energy As anaerobic respiration produces carbon dioxide, measuring how much is produced by each sugar can determine whether yeast enzymes can use that type of sugar. Materials and Apparatus 5 test tubes Galactose 5 fermentation tubes Fructose Distilled water Sorbose Water bath Yeast Glucose Method Place 10 drops of Glucose in a fermentation tube and add 10 drops of yeast to it, fill to the top with distilled water. ...read more.


OH ? H ? C ? OH ? HO ? C ? H ? ??C5 H ? C ? OH ? H ? C ? OH ? H ? C ? OH ? H ? C ? OH ? ??C6 H H H H glucose (dextrose) galactose fructose sorbose carbon number Sources of error/limitations Source of error Why? How does it affect the results? The tubes can become misty during the experiment. This makes it hard to see, and measure the correct length. A 100% error both ways, as it is being measured in mm. The test tubes were not mixed properly. The yeast and sugar may not have much chance to react, as they would normally. The sugars which react with the yeast may not produce the expected amount of CO2 . Turning the tubes upside down. When turning the tubes upside down, some of the solution may come out of the bottom and lower the volume. Less of the sugar solution for the yeast to act on. Atmospheric pressure. The atmospheric pressure is changing all the time, so it may speed up the reaction. Increasing the rate of reaction Using a ruler Not a very reliable way of measuring lengths, as a persons hand may not be steady. ...read more.


C ? OH ? ??C4 H ? C ? OH ? ??C5 Here are the formulas for Mannose and Arabinose: H ? C = = O ? H ? C = = O ? ??C1 HO ? C ? H ? H ? C ? O ? ??C2 HO ? C ? H ? HO ? C ? H ? ??C3 H ? C ? OH ? HO ? C ? H ? ??C4 H ? C ? OH ? H ? C ? O ? ??C5 H ? C ? OH ? H ??C6 H mannose arabinose Carbon number Enzymes act on the active site in a substrate, in this particular case the yeast enzyme acts on the carbon bonds 4 and 5 to bind to the substrate, the sugar. The yeast binds to the sugar as its energy to start respiration. The explanation for enzymes being specific is that an enzyme is like a key and a substrate is like a lock. Only a particular enzyme can bind to a particular substrate. In this experiment the carbon bonds 4 and 5 were the specific parts of the substrate that needed to be present for the reaction to take place. The lock and key hypothesis: Conclusion When the enzyme yeast acts on sugars during fermentation it acts on the carbon bonds 4 and 5. ...read more.

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