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Investigating the effects of surface area on the rate of enzyme reactions.

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Introduction

AS Biology Coursework assignment Investigating the effects of surface area on the rate of enzyme reactions By Scott Humm Introduction Enzymes basically are biological catalysts. What this means is they have the ability to speed up reactions without actually being used up themselves. Enzymes are globular proteins and they have a three-dimensional shape, which is very precise and never varies between two examples of the same protein. The active site for all molecules of the same enzyme will be made up of the same arrangement of amino acids. This exact shape and arrangement of amino acids enables the enzymes to be highly specific and this defines which substrate they bind to in the active site. Because they are so specific, enzymes are thought to catalyse substrate into two different products by the "Lock and Key hypothesis". Diagram taken from http://schools.moe.edu.sg/chijsjc/Biology/Enzyme/enzyme.htm This diagram shows how enzymes catalyse the breakdown of a substrate molecule into two products. The only way that another molecule can bind with an enzyme's active site is if it is an inhibitor. Inhibitors are molecules that can bind with the active site briefly causing competition between itself and any substrate molecules. When there is a very high concentration of inhibitors, substrate molecules do not bind with active sites as easily because there are less of them. This slows down the reaction, and is very useful if someone has drunken anti-freeze. Another type of inhibitors is non-competitive irreversible inhibitors. They remain in the active site permanently, and this means there is no competition at all. This is how the antibiotic Penicillin works. A different kind of inhibitor binds elsewhere on the enzyme, rather than in the active site. ...read more.

Middle

While doing the experiment, I realized quite a few flaws. Firstly, the gas syringe barely moved when the gas was being produced. This may have been due to friction in the syringe, and because of this problem I will change the experiment. The other problem was that when I pushed the bung in the conical flask, the gas inside the conical flask was forced into the syringe, meaning that there would be less gas evolved than shown on the syringe. Method Because of the problems involved in using the gas syringe, I have decided to use this equipment instead: Other equipment used not in diagram: 25cm3 measuring cylinder, razor blade, wooden tile, ruler, #5 cork borer, and thermometer. * Pour water into the trough, and into the graduated burette from the tap. * Put the burette in the trough of water so that no gas enters it. Make sure the delivery tube is not in the burette at this point. * Accurately measure out 25cm� of 20Vol. Hydrogen Peroxide making sure there are no bubbles in it. * Pour this hydrogen peroxide in the conical flask taking care not to spill any. * Using a number 5 cork borer, get a tube of potato. With the razor, cut the potato to exactly to 5cm, and make sure that the ends are cut perpendicular to the side of the potato. * Drop the potato into the hydrogen peroxide and quickly push the bung into the conical flask. * Pump the bung for exactly 20 seconds removing all the gas from inside the conical flask, all the while making sure that the delivery tube isn't inside the graduated burette. ...read more.

Conclusion

This way, I may get more accurate results because using the initial rate of reaction is the best indication of the actual rate of reaction. I only took three readings each of five different surface areas. If I were to redo the experiment, I would do more surface areas, and more repeat readings. The reason for this is that if you take more readings, then you are more likely to get a far more accurate set of results. Of the three repeat readings I did for each surface area, my results were reasonably similar. The relatively low numbers from Standard Deviation show this. (From my results table.) This means that my results are quite reliable. To prove my prediction (that after a certain point, an increase in surface area does not affect the rate of reaction) I could use less substrate. The reason for this is that once all the substrate is being used up, then there are free active sites doing nothing. The less substrate there is, the quicker this point will come, and the graph should level off. I would redo the experiment using 15cm3 of hydrogen peroxide rather than 25cm3. I would also take more readings just to be sure; I would take readings of the 5cm piece of potato being cut into 25 pieces, and 30 pieces. With the extra results and lower substrate concentration, the graph is almost certainly going to level off, and this will be clearly visible too. Safety: At all times, gloves and goggles were worn because hydrogen peroxide is a very dangerous chemical. If it is gotten on your skin or in your eyes, it is very irritating, and may burn. Care was also taken to make sure that the razor blades were used safely and correctly. As an extra precaution, lab coats could have been worn, but this is not particularly necessary. ...read more.

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Here's what a teacher thought of this essay

4 star(s)

This is a well written report that has a good structure and includes a lot of detail.
1. The introduction is strong and includes relevant information. The information should be referenced though.
2. The variables section is very well written and concise.
3. All of the equipment uses should be listed.
4. The conclusion is too brief and does not use the data to back up the pattern.
5. The evaluation is good but could be improved by referring back to the data more, in particularly the standard deviation.
****(4 stars)

Marked by teacher Luke Smithen 08/05/2013

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