The effect of the concentration of the substrate on an enzyme.

Biology coursework

Planning

The investigation that I am going to do is a study into the effect of the concentration of the substrate on an enzyme.

Enzymes:

Enzymes are globular proteins, which act as biological catalysts. They lower the activation energy, the activation energy is the initial energy needed to break the bonds, to start the reaction. Amino acids with hydrophilic side chains are found on the outside on the enzyme, this makes the enzyme soluble, this is important as the amino acids that have hydrophobic side chains are found in the centre of the enzyme. However only a small number of amino acids are found on the active site. They are able to temporarily bind, using hydrogen bonds with the substrate molecules due to a region know as the active site. Because enzymes are proteins their activity can be affected by pH and temperature. The catalytic ability of enzymes depends on their three-dimensional shape; this is more commonly referred to as the enzymes tertiary structure. During an enzyme catalysed reaction a transition occurs during which the reactants together with the bound enzyme are referred to as the enzyme substrate complex.

The way the substrate fits into the enzyme can be described in two ways; Firstly the lock and key mechanism, the substrate is the key and the enzyme is a lock, the two fit together perfectly.

However recently a new hypothesis has been put forward this is called the induced fit, this states that the enzyme changes shape when the substrate molecule binds to the active site. The substrate and active site aren’t perfectly matched until the substrate has bound to the active site because the binding of the substrate causes a change in the shape of the active site.

Once the product(s) has been formed the bonds between the side chains of the amino acid and the products are broken and the product is released. Enzymes are unaltered at the end of the reaction. The enzyme can then receive more substrate after the reaction has finished. The ratio of the substrate and the product determines whether the reaction is forwards or backwards. The other important thing to note is that the enzyme alters the speed of the reaction but it will not change the equilibrium. Nor allow a reaction to happen that wouldn’t happen in its absence.

Factors affecting the rate of enzyme catalysed reactions

The activity of enzymes is strongly affected by changes in pH and temperature. Each enzyme works best at a certain pH and temperature, its activity decreasing at values above and below that point. This is because of the importance of tertiary structure (i.e. shape) in enzyme function and forces, e.g., ionic interactions and hydrogen bonds, in determining that shape.

Enzymes have an optimum pH at which they work fastest. For most enzymes this is about pH 7-8 (physiological pH of most cells), but a few enzymes can ...