The object of this experiment is to measure the effect of the concentration of the enzyme, amylase, on the rate of degradation of the starch and the effect of the chloride ion concentration in the solvent on enzyme activity. Also, the other object is to discuss the comparison between starch and cellulose digestion. Introduction: Starch is a polysaccharide and it is the major storage carbohydrate in plants where it is found in the plastids. It is made up of two types of polymers.
One is amylose, the smaller linear and helical polymer, made up of many glucose molecules joined by ? 1> 4 glycosidic bonds. The other larger polymer is amylopectin. It has a branched structure with many ? 1> 4 glycosidic bonds between glucose molecules and ? 1> 6 glycosidic bonds at branch points. Pure starch is in the form of a white powder which is tasteless and has no odor. It is insoluble in cold water. (Brown, W. H. & Poon, T, 2005) Cellulose is another polysaccharide found in the cell walls of plants.
It is made up of hundreds of linear chains of glucose molecules linked by ? 1> 4 glycosidic bonds. Cellulose is a straight chain structure because the ? 1> 4 linkage causes the glucose molecule to rotate 180 degrees. The many chains of cellulose are packed closely together by the hydrogen bonds existing between the hydroxyl groups of glucose molecules. These bonds contribute to the strength of the molecule. Cellulose is also odorless and tasteless and is insoluble in water (Young, Raymond ,1986).
Starch is a major component of the human diet. For the digestion of starch, the enzyme amylase is needed which is present in the saliva and is also present in pancreatic secretions. This amylase breaks down starch into maltose, glucose, and limit dextrin. This enzyme works at an optimum pH of 6. 7-7. 0. Like for other enzymes, the greater the concentration of amylase present, the faster the digestion of starch would be. Also, chloride ions are coenzymes for this reaction and act as the allosteric activators of this enzyme.
This means that the digestion of starch by amylase will only work in the presence of chloride ions (Thomas J. A. , Spradlin J. E. , Dygert S,1971). This experiment shows how the digestion of starch is carried out in the digestive tract by amylase and the conditions that are required for this reaction to take place. Method: to be inserted by the Results: a) This is a graph of the amount of the enzyme amylase in ml against the rate of reaction, taken as the reciprocal of the reaction time.
Here, a linear relationship is seen and as the amount of the enzyme increases, so does the rate of the reaction. b) This is a graph of the chloride ion concentration in ? mol/tube against the rate of the reaction, taken as the reciprocal of the reaction time. This shows that as the concentration of chloride ions present increases, the rate of the reaction also increases. c) The ratio of the rates of digestion of these polysaccharides by salivary enzymes to bacterial enzymes can be approximately 10:1. This is because of the differences in the structures of starch and cellulose.
Starch has just simple covalent bonds in its structure while cellulose has covalent as well as the stronger hydrogen bonds present to stabilize it. This is why it takes a longer time for bacterial enzymes to degrade cellulose compared to the time required to degrade starch. Discussion: The relationship that should exist between the rate of a reaction and the concentration of an enzyme should be a linear relation. This means that as the concentration of the enzyme increases, more active sites are present for the reaction to take place on, and so the overall reaction proceeds at a faster rate.
The graph that we obtained from this experiment justifies this hypothesis because in it, there is a similar linear relation between the concentration of amylase and the rate of the reaction. After comparing the graph I obtained with two other students I realized that the enzyme that I used for my experiment was less active than the enzymes others used. It can be seen that when using the same amount of enzyme as the other students, the rate of my reaction is comparatively slower. For example, when using 5ml of enzyme solution of the same concentration, my reaction rate was around 0.
25 and others got a rate of around 0. 6 or more. That is greater than two times the difference in reaction rates. However, an error could have occurred if some of the enzymes supplied for the reaction were already denatured. In my graph of chloride concentration against the reaction rate, the shape of the curve is somewhat like this. In the beginning there is a great increase in the rate of reaction for a small increase in chloride concentration. However, as the concentration is further increased, the rate does not increase as much and the curve later flattens out.
This means that a Vmax is reached and no matter how much the concentration is increased, there will be no more increase in the rate (Thomas J. A. , Spradlin J. E. , Dygert S,1971). This is because all the binding sites on the enzyme for chloride ions get occupied and addition of more chloride ions will have no effect. For example, in my graph, there is a greater difference in the rate of reaction between the initial change in concentration from 0 to 0. 2 ml than between the change in concentration between 1 and 2 ml.
The digestion of starch takes place in the presence of oxygen while the digestion of cellulose is an anaerobic process carried out by bacteria in the stomach of ruminants. Also, ruminants have to regurgitate their food back into the mouth to chew and break down the cellulose further. However, breakdown of starch is not that complex and can be done just once in the mouth. Due to the anaerobic degradation of cellulose, methane gas is produced in these ruminants (Van Soest, Peter J,1994). There is no methane gas produced by animals feeding on starch.
Also, the activity levels of animals feeding on starch is greater because the digestion process requires a shorter time, while in ruminants, the digestion takes a long time. Conclusion: Therefore, the rate of the reaction is directly proportional to the enzyme concentration and also increases in proportion to the concentration of its coenzymes to an extent. References: • Brown, W. H. & Poon, T. (2005). Introduction to organic chemistry (3rd ed. ). Wiley • Young, Raymond (1986). Cellulose structure modification and hydrolysis. New
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