The effect of enzyme concentration on the rate of reaction.

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GCSE Science

The effect of enzyme concentration
on the rate of reaction

Maria Mulvany                               Ashlawn School                         Candidate number: 8160

The effect of enzyme concentration on the rate of reaction

Aim: To find out how the concentration of enzyme effects changes in the rate of reaction

BACKGROUND INFORMATION ON ENZYMES

Enzymes are globular proteins, coiled into a precise three-dimensional shape.

They are biological catalysts, speeding up chemical reactions without being affected or used up.

Enzymes speed up reactions where molecules are split or joined together. The molecule, or molecules in the reaction bind to a special feature on the enzyme called the active site.

The enzyme is folded in such a way that the catalytic amino acids are positioned in a region forming the active site. it is usually a depression or groove on the surface of the enzyme  The active site has a complimentary shape to that of the substrate, allowing a perfect fit. This is describing the lock and key theory, where the enzyme is the lock and the substrate is the key.(see figure A). This theory has been modified to the induced fit hypothesis. This states that when the enzyme and the substrate bind, it induces the enzyme structure to fit. (see figure B).  

In the particular example shown in the diagram, the substrate is split into two products. Each enzyme works with a particular substrate, it is specific to that substrate.

In the diagram the substrate binds to the enzyme. The substrate is held to the active site by temporary bonds that form between the substrate and some of the R groups of the enzyme’s amino acids. The enzyme holds the substrate or substrates in such a way that they can react more easily. This lowers the amount of energy needed for the reaction to occur, it lowers the activation energy. Without enzymes, reactions in living cells would occur very slowly, because the temperature in the cell or energy available is too low. An enzyme enables reactions to occur at lower temperatures, thus speeding up the reaction.

Although enzymes are not affected when it catalyses reactions, it has limiting factors that affect the activity of the enzyme. This was considered when planning the experiment. The limiting factors are temperature, pH, substrate concentration, enzyme concentration, inhibitors and cofactors.

Temperature

As the temperature increases, the enzyme and substrate molecules move faster as more heat energy is transferred to kinetic energy. In a decomposition reaction more energy increases the chance of collisions and so the rate at which the products are formed also increases. If the temperature continues to rise above a certain point, above the optimum temperature, there is a gradual decrease in reaction rate as the hydrogen bonds in the enzyme molecules would eventually break and more enzymes become denatured. This would alter the precise three-dimensional shape of the enzyme, preventing substrates binding onto the active site. The enzyme will become denatured.

pH

Each enzyme has an optimum pH at which the substrate best fits the active site. Some enzymes work best in acidic conditions e.g. Pepsin in the stomach and some work best in a neutral environment e.g. amylase in the mouth. A change in pH from the optimum level increases or decreases the concentration of hydrogen ions. The lower the pH the more hydrogen ions are present. The hydrogen ions can interact with the R groups of the amino acids in the enzyme if the concentration is too high or low. This changes the way the R groups bond with each other, effecting its shape. If the pH is dramatically changed from its optimum then the enzyme will denature.  

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Substrate concentration

Increasing the substrate concentration will increase the rate of reaction, as there are more substrate molecules to bind with the enzyme’s active sites. However if the substrate concentration carries on increasing, there is a point where the enzyme is working at its maximum possible rate and so additional substrate molecules that are not bound to the enzyme will not affect the rate of reaction.

Enzyme concentration

An increase in enzyme molecules in a given volume increases the rate of reaction, as there are more active sites to aid reactions at one time. This is ...

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The effect of enzyme concentration on the rate of reaction.
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  • Level
    GCSE
  • Subject
    Science
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