Investigating enzyme catalysed reactions.

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Biology Coursework

Investigating enzyme catalysed reactions

Introduction

For my biology coursework I will be investigating enzyme catalysed reactions and their effects. In this project I hope to extend my knowledge of enzymes and catalysts and research my own experiment that will further and confirm my findings. I will examine how the concentration of the substrate hydrogen peroxide (H202) affects the rate of the reaction of the enzyme catalyses.

Background information

Enzymes

Enzymes are protein molecules produced by living cells. Each cell contains several hundred enzymes. Enzymes can be defined as biological catalysts because they speed up reactions.

Enzyme reactions may be either anabolic (involved in synthesis) or catabolic (involved in breakdown). The sum total of all these reactions in a living cell or organism constitutes its metabolism. Therefore metabolism consists of anabolism and catabolism.

Enzymes serve to control the chemical reactions that occur within cells and ensure that they proceed at an efficient rate.

Biological catalysts possess the following major properties:

  • All are globular proteins
  • They increase the rate of reaction without being used up
  • Their presence does not alter the properties of the end product
  • A small amount of catalyst effects the change of a large amount of substrate
  • Their activity varies with Ph, temperature, pressure and substrate/enzyme concentrations
  • The catalysed reaction is reversible
  • Enzymes generally catalyse only a single reaction

The energy required to make substrates react is called Activation Energy (   )

The greater the amount of activation energy required, the slower will be the rate of reaction at a given temperature. Enzymes, by functioning as catalysts serve to reduce the activati0on energy required 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.

An enzyme combines with its substrate to form a short-lived enzyme/substrate complex. The chances of a reaction are greatly improved within this complex. Once the reaction has taken place the complex will break up into a product molecule and enzyme molecule.

Living cells carry out many different biochemical reactions, and these reactions are speeded up by the presence of enzymes. All enzymes consist of globular proteins which have the ability of guiding reactions. Certain enzymes require additional non-protein groups to enable them to work efficiently.

The ability of an enzyme to function depends on the specific shape of the protein molecule and this shape is created, by the polypeptide folding.

The two theories for enzyme action:

Lock and key theory

  • A part of the enzyme has a precise shape which, is known as the active site. It is here that the substrate can fit into.
  • In this theory the lock represents the active site and the key represents the substrate.
  • When the substrate fits into the enzyme it forms an enzyme-substrate

Complex and the reaction begin immediately.

  • Certain enzymes break a substrate down into two or more products (catabolic reaction), whilst other enzymes bond two or more substrates together into one product (anabolic reaction).

Induced fit theory

  • The active site is a cavity of a particular shape
  • At first the active site is not the correct shape for the substrate, but the site changes as the substrate approaches the active site becomes a perfect fit
  • After the reaction the active site returns to its normal site.

Lowering of activation energy

  • Every reaction requires energy and enzymes reduce the level of activation energy needed
  • The higher the activation energy the slower the reaction. Enzymes reduce the amount of energy required for a biochemical reaction.

  • When an enzyme binds with a substrate the available energy has a greater effect and the rate of catalysis increases. The conditions for a reaction are very important and the following can effect the rate:
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Concentration of substrate molecule

Concentration of enzyme molecule

Temperature

PH

The effect of enzyme concentration

  1. The proportion of enzyme to substrate molecules is important when considering the rate of an enzyme catalysed reaction. Enzymes work efficiently at very low concentrations, the number of substrate molecules that an enzyme can act upon in a given time is called its turnover number. Substrate molecules fit into the active site and if there are more substrate molecules than enzyme molecules, the number of active sites available will be a limiting factor. The optimum rate of reaction is achieved when all ...

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