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What are 'Enzymes'?

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Introduction

'Enzymes' Enzymes are biological catalysts. A catalyst is defined as a substance that increases the rate of a chemical reaction without itself undergoing any permanent change. Enzymes do precisely this in living things. Without them, the rate of the reactions would be so slow as to cause serious, if not fatal, damage. Enzymes have two main functions: To act as highly specific catalysts, and also to provide a way of controlling reactions, the amount of enzyme determines how quickly the reaction can proceed. Enzymes are usually globular proteins (some have been found to be RNA molecules that can act as enzymes) and have a specific three-dimensional shape. Enzyme molecules have a complicated three-dimensional shape due to the particular way the amino acid chain that makes up the protein is folded. An enzymes three-dimensional shape is called its tertiary structure. A few of the amino acids on the surface of the molecule fold inwards to make a specific indentation, called the active site, into which a particular substrate can fit, this is the where the reactions occur. Enzymes are substrate specific. The active site of each different enzyme has its own particular tertiary structure, so only a substrate with a complementary shape will fit; we say it has a highly specific shape. ...read more.

Middle

The reaction will take place and the product, being a different shape to the substrate, moves away from the active site. The active site then returns to its original shape. This shape adjustment triggers catalysis and helps to explain why enzymes only catalyse specific reactions. Below is a two-dimensional diagram to show the induced fit hypothesis. Reactions proceed because the products have less energy than the substrates. However, most substrates require an input of energy to get the reaction going. The energy required to initiate the reaction is called the activation energy. When the substrate reacts, they need to form a complex called the transition state before the reaction actually occurs. This transition state has a higher energy level than either the substrates or the product. Outside the body, high temperatures often supply the energy required for a reaction. This would be hazardous inside the body though. Fortunately enzymes provide an alternative way with a different transition state and lower activation energy. Below is a graph showing that the activation energy of a reaction is smaller in the presence of an enzyme. The active site is held together by hydrogen bonds and ionic bonds. ...read more.

Conclusion

Similarly some enzymes like acidic conditions, with a pH lower than 5, they are called Acidophiles. Some enzymes also prefer alkaline environments with a pH above 9 they are called alkophiles. Enzyme and substrate concentration can also affect enzyme activity. At low enzyme concentrations there is great competition for the active sites and the rate of reaction is low. As the enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate. Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor. We call this the point of optimal concentration. At a low substrate concentration there are many active sites that are not occupied. This means that the reaction rate is low. When more substrate molecules are added, more enzyme-substrate complexes can be formed. As there are more active sites, and the rate of reaction increases. Eventually, increasing the substrate concentration yet further will have no effect. The active sites will be saturated so no more enzyme-substrate complexes can be formed. We call this the point of optimal concentration. Enzymes are extremely valuable biological catalysts to living organisms as they control biological processes and allow them to take place in the conditions, which occur inside living organisms. Charlotte Nellist Biology Essay Page 1 ...read more.

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