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Year 12 Biology OCR Planning Exercise

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Introduction In this investigation I am going to investigate the effect of calcium ions on the rate at which Rennin Coagulates milk. Rennin, is a protease, which coagulates milk, and is most commonly found in the stomachs of calves, however the rennin which I am going to be using is sourced from Fungi. The calcium ions in this investigation are the enzyme co-factor, which means that they help to form the enzyme-substrate complex by helping mould either the enzyme, or the substrate into a more suitable shape so that they may fit together easier. In this case, the substrate will be the milk protein, Casein. Casein is a protein which makes up approximately 80% of milk proteins (http://www.sciencebyjones.com/milk_notes.htm), and is present in the milk in small, microscopic globules called Casein Micelles. These Micelles are a similar to standard micelles, in the fact that they are composed of proteins which have a hydrophilic head facing towards the outside, and a hydrophobic tail facing to the inside. ...read more.


of Milk that will be used * Volume of Enzyme to be added to the milk * Shake the beaker only once, after the enzyme is added. * Make the end point where the globules of coagulated milk are clearly visible. * Volume of calcium chloride added to solution each time. Preliminary Experiment Prior to devising this plan, I conducted a preliminary experiment in order to determine what volumes of liquids I should ideally use. I initially ran the test using just 10cm3 of milk, however the reaction was happening at too fast a rate to be able to get an accurate result on the time, and when the milk sample reached the end point. So after this, I decided to use 20cm3 of milk and an overall total max concentration of calcium chloride of 1 mol dm-3 and a minimum of zero, in order to get an accurate base of the none calcium assisted enzyme reaction. ...read more.


The reaction will initially be first order; this is where the rate is proportional to the concentration of calcium chloride. However as the concentration increases, the rate becomes zero order, where the enzyme is the limiting factor, due to there being a limited number of active sites to process the protein. Method 1. Prepare the solutions of Calcium Chloride in their respective beakers. 2. Measure out 20cm3 of milk into a 50cm3 beaker. 3. Add 2cm3 of Sodium Citrate to the milk solution in order to remove the calcium that is already present in the milk solution, in order for it to not affect the result. 4. Pour the Milk solution into beaker labelled A and shake to ensure that the milk and calcium chloride are fully 5. Place 1cm3 of the enzyme into the beaker, shake and then start the stopwatch. 6. Dip the Microscope slide into the solution every 5 seconds and observe to see whether any coagulated milk flecks are clearly visible 7. When the coagulated milk flecks are clearly visible on the microscope slide, stop the stopwatch and record the time 8. ...read more.

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