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To investigate the factors of the enzyme hydrogen peroxidase (catalase)

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To investigate the factors of the enzyme hydrogen peroxidase (catalase) Planning Scientific Knowledge A catalase is 'an enzyme found in the blood and in most living cells that catalyses the decomposition of hydrogen peroxide into water and oxygen (Student Reference Library 1992) The Oxford Interactive Encyclopedia, 1997, describes hydrogen peroxide as 'a colourless liquid which is miscible with water... It decomposes on heating, or in the presence of a catalyst, giving water and oxygen.' Enzymes are 'a type of protein found in all living cells.' They '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 owe their activity to the precise three-dimensional shape of their molecules. According to the 'lock-and-key' hypothesis, the substances upon which an enzyme acts (which are known as substrates) fit into a special slot (space) in the enzyme molecule: the active site': A chemical reaction takes place at this site and the products are released, leaving the enzyme unchanged and ready for re-use. This cycle can be repeated as often as 100,000 times per second. Enzymes are very specific in relation to the substrates with which they work, and are normally only effective for one reaction or a group of closely related reactions. 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.' Proteins are 'molecules composed of long chains of amino acids which are linked by peptide bonds... The 'primary' structure of a protein is the order, or sequence, of amino acids in it; different proteins have different primary structures. The amino acid sequence determines the final three-dimensional shape of the protein molecule. The 'secondary' structure of a protein is the regular three-dimensional folding of the polypeptide chain, formed, for example, by hydrogen-bonding between regions of the chain. ...read more.


Then the second reaction with the 7.5v and then the 5v, 2.5v, and 1.25v finally should have the slowest reaction time. I predict this because I know that the higher the concentration the faster a reaction takes place, because there are more particles of reactant to collide with each other. This all means that the 10voles should have the most gas collected and the 1.25 will have the lowest amount collected. I am going to do the experiment twice so I can get two sets of readings for the different volumes of H O . The results should be similar, because I would have used the same amount of celery and the same amount of hydrogen peroxide. Which should give me the same amount of enzymes and hydrogen peroxide molecules colliding together and hence the same results. If the hydrogen peroxide was to be too strong then the reaction probably would not take place at all. This would be because enzymes need to remain in certain acidity levels and temperatures. If the levels of either of these are too high then the enzyme changes shape, disallowing the protein substrates to fit into the enzymes active site. I just have to be careful that no other factor is present because this will affect my results. Apparatus The apparatus that I will be using is hydrogen peroxidase found in celery, hydrogen peroxide, conical flask, burette, connecting tube, measuring cylinders, water bath, water, weighing scales, clamp stand and a stop watch. Obtaining Diagram Method To get an idea of the right amounts of celery and hydrogen peroxide needed, I had to put together any odd amount. I chose to use 50ml of hydrogen peroxide and 3g of celery. I put the celery into the conical flask and held the 1.25v of hydrogen peroxide in the measuring cylinder. After setting up all the equipment, so that the burette was held by the stand and was in the water bath half full with water, I had to pour the hydrogen peroxide into the flask. ...read more.


[a] substrate concentration on the rate of an enzyme-controlled reaction' should look like the graph below- The explanation for the graph is also given, and this explains why the graph for the concentration of H O should in fact be curved: 'For a given enzyme concentration, the rate of an enzyme reaction increases with increasing substrate concentration (fig 4.7). The theoretical maximum rate (Vmax) is never quite obtained, but there comes a point when any further increase in substrate concentration produces no significant change in reaction rate. This is because at high substrate concentrations the active sites of the enzyme molecules at any given moment are virtually saturated with substrate. Thus any extra substrate has to wit until the enzyme/substrate complex has released the products before it may itself enter the active site of the enzyme.' However, I did not obtain obvious curves for all the results. That may be because I did not take the measurements over a long enough period or because of slight inaccuracies in writing down the results. Also, at times the celery was not cut to such small sizes as other times, which would make a difference to the rate of reaction because the larger a surface area is the more collisions there are and the higher the rate of reaction. If I were to redo this experiment I would make sure that all the celery was cut to a similar size, because then my readings would not have been affected and all the lines on the graph would have been curves rather than a few. To further the work on factors that affect the rate of reaction between a catalase and hydrogen peroxide I would check other factors. I have already proved that the concentration affects the rate of the reaction, and have seen basically that so does the surface area. Now all that needs investigating is the pH, temperature, stirring, pressure and the catalase amount. But I am sure that these affect the rate of reaction too. ...read more.

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