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Effect of temperature on the action of an enzyme

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Effect of temperature on the action of an enzyme Introduction Enzymes are catalysts that speed up biochemical reactions. Most compounds found in cells are very stable and without enzymes would not react at any useful rate. Enzymes are proteins. Their molecular shape is important, because the enzyme needs to form a precise fit with the substrate - the molecule or molecules involved in the reaction. Only a small part of the enzyme makes contact with the substrate; this part is known as the active site. The shape of the active site allows the substrate to fit perfectly, and to be held in place by temporary bonds, which form between the substrate and some of the R groups of the enzymes amino acids. This combined structure is termed the enzyme-substrate complex. The enzyme may catalyse a reaction in which the substrate molecule is split into two or more molecules. Alternatively, it may catalyse the joining together of two molecules, as when making a dipeptide. Interaction between the R groups of the enzyme and the atoms of the substrate can break or encourage formation of, bonds in the substrate molecule, forming one, two or more products. When the reaction is complete, the enzyme is unchanged by this process, so it is now available to receive another substrate molecule. ...read more.


However, if we go on increasing substrate concentration, keeping the enzyme concentration constant, there comes a point where every enzyme active site is working continuously. If more substrate is added, the enzyme simply cannot work faster; the molecules are effectively queuing up for an active site to become vacant. I will keep the substrate concentration at 25cm3, 1.0%. As this is what I used in my preliminary work and it gave reliable and accurate results. Measuring methods The way that I will measure how long it takes for the reaction to cease is to add iodine to a drop of the mixture, it should turn blue if starch is present, if starch isn't present the iodine will not change colour. I will measure the colour change by sight, as the blue colour will vary depending on the amount of starch present. The darker the colour the more starch there is in the mixture. I will use diastase solution (25cm3, 1.0%), and starch solution (25cm3, 1.0%). These solutions proved reliable and gave good results in my preliminary experiment. I could use a colorimeter to be precise, but through my preliminary experiment I found this unnecessary. Prediction I predict that the higher the temperature the higher the rate of reaction. This means that the molecules will move faster and have more energy. ...read more.


5. At intervals of one minute test each tube for the presence of starch-diastase mixture, place it on a white tile, and add one drop of iodine solution. Use one glass rod for each tube and a separate one for the iodine solution 6. Make a complete record of your observations, noting how long it takes in each case before a blue colour ceases to be given when iodine is added to the mixture. I chose this method, as this is the same method that I used in my preliminary experiment so I know it is reliable. Risk Assessment All glassware must be handled with appropriate care, especially when it is immersed in a hot water bath, also take care with the hot water as it is a burn hazard at 100oC. Results Table Temperature (oC) Time (min) Room temp 25oC 40oC 60oC 100oC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 (From my preliminary experiment I found it useful to create a scale for the variation of the colour of the solution when iodine was added. 0 being very dark and 5 being light) The add results to the table you use the scale to find out what number you think best represents the colour and then add it into the correct time row and the correct temperature column. Alan Julyam Biology Coursework Ms Sweeney ...read more.

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