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Investigating the Effect of Substrate Concentration on Catalase

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Introduction

Investigating the Effect of Substrate Concentration on Catalase Aim To investigate the effect of substrate concentration the enzyme catalase using the decomposition reaction of hydrogen peroxide and measuring the volume of oxygen produced. Hypothesis Enzymes are globular protein molecules, which catalyse chemical reactions and therefore speed up the rate of the reaction and yet remain unchanged (Jones, Fosbery and Taylor, 2000). The enzyme's structure, as it is three-dimensional, is determined by the sequence of amino acids. A few of these amino acids make up an active site. This is a cavity in which other molecule(s) can bind; this molecule is known as the substrate. The substrate is held in the active site by hydrogen bonds that temporarily form between the hydrophilic R-groups of the active site and on the substrate molecule. The structure that results is the enzyme-substrate complex. The compounds on which the enzymes act upon are called substrates. The enzyme could either catalyse a reaction to breakdown into two or molecules or it could help to create bonds in the substrate molecules. The molecules that form from either of these reactions are called products. The activation energy is the initial energy needed for a reaction to occur. Enzymes lower the activation energy in order for reactions to happen more easily. Enzymes are used for reactions that take place very slowly or would normally occur at very high temperatures. Each enzyme has a specific shape (the lock), which only a specific substrate (the key) can attach to, making enzymes specific to the reactions that they catalyse (Toole and Toole, 2004). This is the lock and key theory. However, the actual process is slightly more complicated than this and is known as the induced fit theory. The enzyme is slightly flexible and can therefore mould itself to fit perfectly around the substrate. As the shape is changed, the activation energy is lowered as a strain is put on the substrate molecule. ...read more.

Middle

This will be the most accurate as there is less room for error. 2cm3 Syringe 0.1cm3 To measure out the 2cm3 catalase, a 2cm3 syringe will be more accurate as it is has smaller graduations and so there should be fewer inaccuracies; it is more precise. 25cm3 Measuring Cylinder 1cm3 This is to measure out the volumes that are larger than 10cm3 as there are no accessible syringes that take up 25cm3. It is not very accurate to use a 10cm3 for 25cm3 and to measure out three times and so a measuring cylinder will be used. This is still quite precise as it is graduated in 1cm3. Delivery tube with bung N/A The delivery tube will be inserted into the bottom of the burette in the trough. The bung will be placed on the conical flask. This ensures that the oxygen will travel directly from the burette to the conical flask. Burette 0.1cm3 The burette holds 50cm3 and is the most suitable apparatus to enable the water to be displaced by the volume of oxygen produced and in order to measure the oxygen. The 0.1cm3 graduations are very precise and should ensure high levels of accuracy. Clamp Stand N/A The clamp stand is needed to hold up the burette and ensure that is held up straight in the trough so that the readings can be read as accurately as possible. Stop clock 0.01s This is to measure the time, as readings will need to be taken with intervals of 15s and recorded the nearest whole second. The stop clock will accurately record keep the time so that the results can be taken at the correct times. Even though the stop clock has a sensitivity of 0.01s, time will be written to the nearest second, as no more accuracy is needed for this. 50cm3 Beaker 10cm3 The beaker will be used to fill up the burette. ...read more.

Conclusion

For 1, 2 and 3% concentration, the error bars are generally on the smaller side whereas for the 4 and 5% concentrations, the error bars are mostly quite large, suggesting the 4 and 5% concentrations results were less reliable. The most likely reason for the error bars being so different is the displacement of water. When the concentration is higher, more oxygen is produced and at a faster rate. This makes it hard to read as the bubbles produced speed past one another. When the concentration is lower, the oxygen is produced at a much slower rate and so the bubbles do not tend to move as quickly, making it easier to read. This leads to larger error bars in the higher concentrations as is more difficult to tell the exact volume of oxygen. The standard deviation shows the spread of the data from the mean. Most of the values do not vary very much. It is only really in the 5% concentration graph from 45s onwards that there are large standard deviations. This means that the range is very big and so these results are not very reliable as the repeats were not very consistent like the rest of the data. The validity depends on the range and reliability of the measurements. The conclusion drawn from the results and graphs is that the substrate concentration is directly proportional to the volume of oxygen produced, supporting my hypothesis. The range of my planned values were good, however from the given data it appears that I could have planned to use up to 5% concentration as it worked rather well. The experiment was quite fair and the control variables were all successfully controlled and the method was rather precise. It was also quite accurate despite all the possible inaccuracies. Therefore I think my results are valid enough to support my hypothesis, although many more repeats would need to be carried out in order to prove the hypothesis. ...read more.

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