Enzymes - complex three-dimensional globular proteins, with hydrophillic side chains which makes them soluble

Authors Avatar

Enzyme Coursework

Introduction

Enzymes are complex three-dimensional globular proteins, with hydrophillic side chains which makes them soluble. The enzyme molecule is normally larger than the molecule of the substrate it acts upon, but only a small part comes into contact with the substrate. This region is called the active site so the substrate of the enzyme can bind to it. The active site has such a shape that it allows the substrate to fit perfectly, and to be held in place by temporary bonds. The bonds form between the substrate and some of the R- groups of the enzymes amino acids.

Enzymes are very specific because the enzyme has a particular shape into which the substrate fit perfectly. This is known as the ‘lock and key’ hypothesis where the substrate is the key whose shape is complementary to the enzyme or lock.

Fig.1

Fig.1 shows that when a substrate complex is formed it is ‘activated’ into forming the products of the reaction. Once formed, the products no longer fit into the active site and escape into the surrounding medium, leaving the active site and escape into the surrounding medium, leaving the active site free to receive further substrate molecules.

Enzymes are biological catalysts, each enzyme is specific to a particular reaction or group of similar reactions. Catalyst is a substance that alters the rate of reaction but remains chemically unchanged at the end of the reaction. Catalysts speed up reactions. They do this by providing an alternative pathway for the reaction. Enzymes, by functioning as catalysts, reduce the activation energy needed for a chemical reaction to take place. They speed up the overall rate without altering, to any great extent, the temperature at which it occurs.

Prediction

As the temperature increases, kinetic energy of the substrate and enzyme molecules increases and so they move faster. The faster they move, the more collisions will be with one another and the greater the rate of reaction. Also as the temperature increases the atoms vibrate more and this causes the hydrogen bonds to break as they are not very strong. I predict that the rate doubles for every 10oC rise in temperature until the maximum temperature has been reached. Energy is given to a system that causes the enzyme and substrate molecules to move faster. This increases the chances of random collisions, beyond the optimum temperature. Hydrogen bonds that hold the 3 dimensional shape of the active site together is altered to such an extent that the active sites no longer complementary to the substrate. The enzyme is then said to be denatured.

However if the temperature decreases, then the particles lose energy and they begin to slow down. This in turn would give a slower rate of reaction. In time the enzyme becomes frozen and stops, but starts working again when we raise the temperature.

I predict that the rate of reaction will increase up to a temperature of 37oC and I wouldn’t expect to see a reaction at 0oC because it is too cold for the enzyme to work.

Our body temperatures are at 37oC and seeing as we have enzymes inside us this tells us that the optimum temperature of an enzyme is around 37oC. This is to make sure the reactions take place close to their maximum rate.

pH is a measure of acidity. The stronger the acid the more readily it releases its hydrogen ion. The stronger the base the more readily it accepts the hydrogen ion. Amino acids are described as an acid base or neutral. This property is converted given by the reactive side of the chain. It is these side chains that are responsible for forming the Hydrogen bonds. The hydrogen bonds are responsible for forming the secondary and tertiary structures of the enzyme, and for giving shape to the active site. Enzymes operate within a very narrow range of pH. So I predict that if placed in a solution that’s either too acidic or too basic, the hydrogen bonds within the site become destabilised. This changes the shape of the site so it is no longer complementary to the shape of the substrate. The enzyme is denatured.

Join now!

As the substrate concentration increases, the initial rate of reaction also increases. Again this is only what we would expect: the more substrate molecules there are around, the more often an enzymes active site can bind with one. If we keep increasing the substrate concentration keeping the enzyme concentration constant, there comes a point where every enzyme’s active site is working continuously. If more substrate is added the enzyme cannot work faster: substrate molecules are ‘queuing up’ for an active site to become free. The active site of an enzyme may be used again and again. Therefore enzymes work efficiently ...

This is a preview of the whole essay