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An investigation into the effect of substrate concentration on the activity of the enzyme catalase in potato tissue.

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Introduction

AS Biology Coursework Experiment. An investigation into the effect of substrate concentration on the activity of the enzyme catalase in potato tissue. Introduction. Enzymes are globular protein molecules known commonly as Biological Catalysts. The definition of a catalyst is a substance that can be used to speed up the rate of a chemical reaction while remaining unaffected and unchanged after the reaction. The enzyme's ability to act relies strongly upon the specific shape of the protein molecule, which is coiled into a precise three-dimensional shape. This specific shape is the cleft or depression, which other molecules (substrates) fit into perfectly; this part of the enzyme, is called the active site. The tertiary folding of the polypeptides causes the intricate specific shape of the active site. The substrates are held in the active site by forming temporary bonds with the hydrophilic R groups of the enzyme's amino acids. Here we have a diagram showing the 'lock and key' theory of enzyme action. The substrate (key) is shown fitting perfectly into the active site (lock). The substrate binds to the enzyme and forms an enzyme-substrate complex. The reaction then takes place immediately and a substrate is either broken down into two or more products (catabolic reaction) or two or more substrates are bonded to make one product (anabolic reaction). The 'induced fit' theory states that initially the active site is no the perfect shape of the substrate but as it approaches, the shape of the active site changes to make the perfect fit. ...read more.

Middle

I am going to use the water displacement method to collect the gas. I am going to make the oxygen gas displace some water in a measuring cylinder. The experiments were carried at a standard room temperature, and volumes, concentrations and quantities were measured to exactly the same values for each trial. Here is a predicted formula for the reaction: 2H202 catalase 2H20 + 02 I predict that an increase in the substrate (Hydrogen Peroxide 2vol) concentration will result in an increase in reaction rate. I also feel that after a certain point, the rate of reaction will decrease due to an excess of substrate and therefore a queue for reaction will occur. Catalase is able to speed up the decomposition of Hydrogen peroxide because the shape of its active site matches the shape of the Hydrogen peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an Anabolic Reaction. Diagram of Apparatus Method: First of all I set up the apparatus as in the diagram. Using a cork borer, I cut five equally sized cylinders of potato tissue. I then placed each of these cylinders into their own test tubes. Attached to the bung of the tube was a delivery tube, which we could insert a syringe into. From the bung, there was another delivery tube that was long enough to reach another test tube. ...read more.

Conclusion

These errors would be due to faulty/ inaccurate measurements of substrate and/ or catalase, differing temperatures, and surface areas not exactly the same. It is therefore possible to say that any imbalances in any of the factors affecting rate of reaction would have given me an inaccurate set of results. Higher levels of accuracy would have been maintained using thermometers to keep a constant temperature, pieces of potato exactly the same, measurements of volumes of liquid taken at higher accuracy's, and time periods counted to an even more accurate level. As using catalase founded in potatoes, the desired amount was hard to measure, however, measuring the amount of potato wasn�t difficult although that piece could contain different amounts of catalase compared to another piece. The theoretical maximum rate of reaction is when all the sites are being used but in reality this theoretical maximum is never reached due to the fact that not all active sites are being used at the same time. The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum. The time taken to fit into and leave the active site is the limiting factor in the rate of reaction. Given the laboratory conditions, my results (although not perfect) give a clear indication of patterns and show clearly the effects of increasing substrate concentrations (along with increases in surface area). ...read more.

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