Theeffects of amylase concentration on the breakdown of starch

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The effects of amylase concentration on the breakdown of starch

Plan

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I will be investigating how altering the concentration of amylase (the enzyme) affects the rate at which starch (the substrate) is broken down.

Amylase is an enzyme that hydrolyses starch into maltose. The hydrolysis involves adding one molecule of water across a glycosidic bond. Amylase is often found in two forms, α amylase that breaks down starch into fragments ten residues long, and β amylase that then breaks these into maltose (two glucose residues)

Enzymes are proteins that act as biological catalysts in biochemical reactions, and so increase the rate of reaction by lowering the activation energy. Enzymes are referred to as specific, as each specific enzyme will only catalyse a specific reaction. For example, amylase only breaks down starch, and attacks two specific glycosidic bonds.

Enzymes are very often quaternary structured, globular proteins that consist of two or more polypeptide chains that- due to intermolecular bonding (including hydrogen, ionic and disulphide bridge bonding)-give rise to a complex three-dimensional shape. This complex three-dimensional shape results in the formation of an active site. Active sites are areas on an enzymes surface that are specially designed to bond with the substrate molecules, to allow the substrate to be acted upon, in this case starch.

In order for this reaction to occur in the first place, specific conditions must be met and are explained through collision theory.

The collision theory states that for two molecules to react they must not only collide, but they must collide at the right orientation and with enough kinetic energy to induce a reaction, therefore these conditions and their applications must be considered when evaluating my final results.

Due to their being only one active site per enzyme, each enzyme is only capable of catalysing one reaction at any one time i.e. only one enzyme-substrate complex can form at any one time. Therefore the higher the numbers of enzymes present the higher the rate of reaction.

 

Hypothesis

I predict that as I increase amylase concentration, the rate at which starch is broken down also increases.

Key Variables

 Temperature:

 Increasing temperature increases the kinetic energy of both enzyme and substrate molecules and so increases the number of collisions between them. This in turn increases the rate of reaction, as more enzyme substrate complexes are likely to form.

However there is a limit to how high a temperature can be raised before it has a detrimental effect. If too much heat is applied and the enzyme molecules gain too much kinetic energy, the intermolecular bonding is tampered with and bonds are destroyed. This directly affects the shape of the active site, and as the enzyme is completely dependant on its specific shape, it renders the enzyme ineffective and is therefore denatured. Therefore an optimum temperature can be reached, whereby enough energy is provided to maximise the number of collisions, while having no effect on the shape of the enzyme.

Therefore the temperature all used solutions will be kept constant throughout the experiment.

The general pattern for an enzymes efficiency at different temperatures is as shown below.

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pH:

Extreme pH levels generally also have a detrimental effect on the efficiency of an enzyme, as they interfere with the intermolecular bonding (tertiary /quaternary structure). Changes in pH levels affect the ionisation of the amino acid residues and alters the shape of the enzyme and consequently its active site. This then leads on to the denaturation of the enzyme, as the substrate molecule is no longer able to attach to its active site. However some enzymes are specifically designed to work more efficiently in more extreme pH levels than others. For example, digestive enzymes (enzymes contained in bile eg.proteases) when released into the stomach are able to work more efficiently at the acidic pH levels than other enzymes. This again gives rise to an optimum pH, whereby a pH most suited to the enzyme can be used to obtain maximum efficiency. The general pattern for an enzymes efficiency at different pH levels is as shown below.

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Therefore the pH of the solution will be kept constant throughout the experiment.

Concentration of substrate (starch):

The concentration of substrate has a direct affect on the rate of reaction. If the concentration of substrate is increased there are more substrate molecules for the enzymes to collide into. Consequently there is a higher chance for successful collisions to occur (collisions that produce enzyme substrate complexes) and this increases the rate of reaction as more of the product is produced. Conversely if the concentration of substrate is decreased this decreases chances for successful collisions to occur and so decreases the rate of reaction.

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Therefore the concentration of starch will be kept constant throughout the experiment.

Volumes of amylase concentrations:

The concentration of amylase solution refers to the number of amylase enzyme molecules in a given volume. However two different volumes of the same concentration of amylase enzyme will contain different numbers of enzyme molecules, and therefore most likely react with starch differently. Therefore to ensure this is a fair test it is necessary to keep all concentrations relative to one volume, so that valid and reliable comparisons can be made.

Therefore the volume of amylase solution must be kept constant throughout the ...

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