Effect of temperature on effectiveness on the Enzyme Pectinase

BIOLOGY

Aim

The aim of the investigation is to find out at which temperature most juice extraction will take place. This will be achieved by the assistance of enzyme Pectinase.

Hypothesis

I predict that the grated apple, which is placed in a test-tube, that is exposed to most appropriate temperatures (temperatures that range closest to the enzymes optimum) shall have the most juice extracted from it. This is due to various reasons, ranging from the enzyme’s structure (shape), it’s properties and it’s size.

The reason as to why the enzyme’s structure affects the grated apple is classic, if we were to use enzyme amylase for example, the enzyme will not affect the rate of juice extraction by a lot because although it can catalyse the apple, it isn’t as well suited to the job as the pectinase enzyme is. So it’s important that we use the enzyme pectinase. Enzymes are globular proteins. They have complex tertiary and often quaternary structure in which polypeptides are folded around each other to form a roughly spherical, or globular shape. The overall 3-Dimensional shape of an enzyme molecule is very important: if it is altered, the enzyme cannot bind to its substrate and so cannot function. Hydrogen bonds, ionic forces and disulphide bridges maintain the shape of an enzyme, and it is when their functions are affected by changes in temperature that we refer to the denaturing of an enzyme.

It must be outlined that enzymes are specific: each enzyme usually catalyses only one reaction. It has been made clear that different enzymes can only catalyse different substrates, but this applies to the majority only. Some enzymes like amylase may catalyse grated apple, but only slightly.

Enzymes combine with their substrates to form temporary enzyme-substrate complexes.
Enzymes are sensitive to surrounding factors such as: temperature.

Another fact about enzyme structure (enzyme-substrate structure) is that the Michaelis Constant (Km or Vmax/2) can be applied. This is very useful as it gives us a good idea of the enzyme pectinase’s turnover number. This may apply to the structure of the enzyme, but as I am not carrying out an experiment to calculate the rate of reaction between enzyme and substrate concentration it will not be necessary to use this hypothesis.

The enzyme’s properties can also affect the rate of juice extraction:

Enzymes work rapidly and each has its own turnover number.
Enzymes are not altered or used up by the reactions they catalyse, so can be used numerous times.
Enzymes are sensitive to surrounding factors such as: temperature etc…

Another property of the enzyme is that it catalyses substrates through the fact that the substrates collide with the enzyme causing the substrate to combine with the enzyme forming the enzyme-substrate complex. It is obvious that the substrate has to collide with the enzyme at a sufficient force and yet more it must be noted that the substrate must collide with the enzyme at a certain angle. This is important because the active site of the enzyme can only take hold of the substrate if it collides in the correct direction facing the active site so that it can fit in to it. This relates to the collision theory.

During a reaction, the substrate fits into a region on the enzyme surface called the active site.

Enzymes speed up by lowering the activation energy needed to get the reaction started.

Now factors that slow down enzyme activity are the inhibitors within the apple. These basically hinder the substrates from attaching to the active site and in some cases the inhibitors may change the overall shape of the active site so that the substrate can no longer fit into the active site.