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Investigating the “lock+key” hypothesis

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Investigating the "lock+key" hypothesis An enzyme is a type of protein found in all living cells. Enzymes act as biological catalysts, allowing all the chemical reactions of metabolism to take place, regulating the speed at which they progress, and providing a means of controlling individual biochemical pathways. Enzymes have a precise 3-dimensional shape. According to the 'lock-and-key' hypothesis, the substances upon which an enzyme acts (which are known as substrates) fit into a special slot in the enzyme molecule - the active site. A chemical reaction takes place at this site and the products are released, leaving the enzyme unchanged. This can be repeated 100,000 times per second. Enzymes are usually only effective for one substrate because each needs a different shaped active site. They function best in particular conditions of temperature and acidity (pH), and their action can be slowed or stopped by inhibitors. Many enzymes need a coenzyme in order to function. The human body contains at least 1,000 different enzymes. Amylase is an enzyme that reacts with starch converting it into glucose molecules. ...read more.


If the reaction is complete and there is no more starch left the mixture will turn light yellow in colour when iodine is added. To make the different concentration enzyme solutions I will mix the enzyme solution with water. The first concentration - 1% will be provided by the teacher but to get 0.8% for example I can mix 0.8 ml of the 1% solution with 0.2 ml of water, to get 0.6% solution - 0.6 ml of enzyme and 0.4 ml of water and so on. I will repeat this experiment twice with five different enzyme concentrations each time - 0.2%, 0.4%, 0.6%, 0.8% and 1%. The experiment will be completed twice to make sure that the results are accurate. I will draw a line graph using the average of the 2 results. From it I will be able to easily view the results and complete the Aim section. Variables Independent Dependent Controlled 1. Amylase concentration 1. Time taken for starch to be catalysed 1. ...read more.


It was sometimes hard to tell when the reaction was complete because different types of iodine we used gave different colours when added to the amylase-starch mixture. Also the volume measurements might not have been very accurate because of the small volumes we used. This may have been the reason why the result for amylase concentration of 0.8% did not fit in with the rest. You can see this clearly from the graph, where the time value for point 0.8% should be slightly lower. If I had infinite time, resources and patience I would keep the experiment the same temperature (e.g. body temperature) all the way through. I could also continue the experiment to include other amylase concentrations. I could also use the substrate (starch) concentration as the independent variable in another experiment. For example in one experiment I researched, the effect of substrate concentration on an enzyme-controlled reaction with two different enzyme concentrations was studied. You could say that an experiment should not have two independent variables but it's more like two sets of results put together on one graph: ...read more.

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