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BIOLOGY A2 LEVEL COURSWORK: THE EFFECT OF BILE SALT ON THE ACTION OF THE ENZYME LIPASE NADA ISSA A2 COURSEWOEK Aim The aim of this investigation is to investigate the affect of bile salts on the action of the enzyme lipase Bile salts: Bile salts are secreted from the liver in the gall bladder, and then passed through the bile duct into the small intestine when food is passing through; they are involved in the emulsification of fats in the intestine, helping in the digestion and absorption of lipids. They also carry waste products to be excreted such as bile pigments. These derive from the breakdown of red blood cells. Bile salts are made up of a bile acid and an associated cation, which are usually amino acids. Bile salts are made up of two parts these are hydrophobic and hydrophilic components. Figure one: The above figure portrays the structure of bile acids. The hydrophobic part of the molecule associates with particles of dietary fat which causes the fat globules to break down into microscopic droplets; this increases the surface area of the fats for digestion by lipases. While the hydrophilic part associates with water which in turn emulsifies the insoluble fat, which is then absorbed through the intestinal wall. The figure illustrated below shows the action of bile salts in emulsifying fats in the intestine. Figure one: The bile acids are made from cholesterol, which is either ingested as part of our diet or derived from hepatic synthesis, which are then conjugated to an amino acid. After the absorption and the emulsification process bile salts are separated from the dietary lipid and are recycled as they return back to the liver for reuse. Bile consists of 98% water, 0.8% bile salt, 0.7% inorganic salts, 0.6%cholesterol and 0.2% bile pigments. In this investigation the presence of bile salts play a crucial role in the experiment as they emulsify the lipids making it easier for the lipase to act on the fats. ...read more.


* Organize table and label all beakers and test tubes clearly - to avoid any confusion as to what they may contain. * Handle sodium carbonate (Na2Co3) and lipase cautiously - if exposed to skin wash instantly. * Ensure equipment is not placed next to the computers so that if any accidents were to take place it will not be next to the computers thereby avoiding lost work or computer crash. Table of results Demonstrated below are my results for each factor of bile salt and the mean figure for each concentration. By the end of each experiment, I obtained a reading for every second within five minutes. However, presenting the results of 300 seconds would seem irrelevant; therefore, I decided to illustrate my tables (shown below) with a reading every 30 seconds, this will provide an overall idea of how much the pH dropped throughout the entire investigation. Table 2 Time (seconds) pH for 0% Bile Trial 1 Trial 2 Trial 3 mean/average 0 10 10 10 10 30 10 10 10 10 60 9.9 9.9 10 9.9 90 8.4 9.9 9.8 9.3 120 8 9.9 9.7 9.2 150 8.1 9 9.6 8.9 180 8 8.8 9.4 8.7 210 7.9 8.7 9.3 8.6 240 7.8 8.6 9.3 8.5 270 7.8 8.5 8.4 8.2 300 7.7 8.4 8 8 Table 3 Time (seconds) pH for 1% Bile Trial 1 Trial 2 Trial 3 mean/average 0 10 10 10 10 30 10 10 10 10 60 10 10 9.8 9.9 90 8.8 9.2 9.9 9 120 8.3 9 9 8.7 150 8.1 8.8 8.7 8.5 180 8 8.7 8.4 8.3 210 7.9 8.6 8.4 8.3 240 7.8 8.5 8.2 8.1 270 7.8 8.4 8 8 300 7.7 8.3 8 8 Table 4 Time (seconds) pH for 2% Bile Trial 1 Trial 2 Trial 3 mean/average 0 9.9 10 10 9.9 30 8.6 10 9.8 9.4 60 8.4 10 9.8 9.4 90 8.1 9.1 9.7 8.9 120 8 9 9.5 8.8 150 7.8 8.8 8.8 8.4 ...read more.


Moreover, I used the same amount of lipase, bile and cream to ensure my experiment was a fair testing, as there was the same amount of enzyme and substrate therefore enough enzyme particles to react with the substrate present. Another crucial point which must be taken into account is the varying activities of bile and lipase as those I used in my experiment was almost definitely extracted from animal (pigs to be more precise). Since humans and animals vary in their body function this would have meant that the affects bile and lipase on my experiment would have been different if I had used bile and lipase maintained from a human source or another animal. Perhaps if the lipase was derived from another specie then it may have been more or less affective. A final point to consider is the Colipase theory; from my research and the results obtained in my experiment it is evident that bile aids the activity of lipase, however, it also limits its optimum potential. The colipase theory explains that colipase allows the enzyme to continue and work at its best rate. Consequently, the rate of reaction will become faster and achieve more abundant collisions and interaction between substrate and enzyme. The lipase is strongly inhibited by bile salts, but is reactivated by colipase. Normally the active site of the lipase is covered by a "lid" however the presence of colipase allows this "lid" is opened thus the active site is exposed allowing lipids to bind. As a result the function of colipase is to bind the substrate and lipase in addition to providing conformational changes. The colipase often allows one enzyme to bind to the triglyceride and the other to the lipase. Overall, my results are relatively reliable although the degree of accuracy can be argued. However, I was still able to gain good results which supported my earlier hypothesis, and also gain my conclusion. Nonetheless, if I were to repeat this experiment I must consider the factors stated above. ...read more.

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