Enzymes - investigate the affect of amylase concentration on starch breakdown into glucose.

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Aim

The aim of this investigation is to investigate the affect of amylase concentration on starch breakdown into glucose. To do this a couple of variable should be brought into consideration. They are the amount of amylase and the time taken for the starch to break down into glucose.

Prediction

I predict that if I increase the concentration of amylase in the starch then the amount of time taken for the starch to break down into glucose will decrease, hence making it’s rate of reaction higher. This is because there will be more active sites for reactions, resulting in more chemical reactions caused by successful collisions between the active site of the amylase and the starch.

The higher the concentration of amylase in the starch then the amount of time taken for the starch to break down into glucose will decrease. This is because there is more amylase in a higher concentration gradient to break down the starch into glucose, thus making the reaction time much less. However there is less amylase in a lower concentration gradient that makes the reaction time longer because there is not enough amylase to break down he starch in one go.

Enzymes are biological catalysts/scissors. They speed up reactions within the body so that they can take place at body temperature. The enzyme is not used up in the reaction and can continue work on other substrate molecules. Enzymes are proteins with a special shape. All enzymes are made up of hundreds of amino acids joined together in a specific way. The protein (enzyme) molecule becomes twisted to form a special 3 dimensional shape, which can combine with a reactant (substrate) molecule, like a fitting in a particular key.

Enzymes combine with reactants, called the substrate. The enzyme allows the products to form the substrate by making and breaking chemical bonds easily.

An enzyme molecule can bring about hundreds of changes like this each second.

The enzyme is not used up at the end of the reaction and can continue to combine with other substrate molecules, forming more products. The enzyme is linked to a specific key, which fits onto a specific substrate (the lock). This is sometimes called the lock and key theory of enzyme action. These diagrams show two ways in which enzymes can bring about a change in the substrate: -

The special shape of a particular enzyme is held together by many different kinds of chemical bonds, it is these, which are affected by temperature (above 40°C) and incorrect pH.

Enzymes only one reaction in which the same end product is formed each time. They act at a certain optimum temperature, usually 36.7°C. Most enzymes are de-activated above 40°C. With most chemical reactions, raising the temperature will only increase the rate of reaction. This is true of enzyme-catalysed reactions, but only up to a point.

As you can see, initially as the temperature is increased so the rate of reaction goes up. You would expect this as the number of molecules possessing the amount of activation energy needed to react is being increased as more heat energy is supplied. The temperature coefficient, or Q10, is used to show the relationship between the reaction rate and a 10°C rise in temperature.

Q10 = Rate of reaction at t°C + 10°C

       Rate of reaction at t°C

Calculate the value of Q10 for the reaction above if the temperature is raised from 25°C to 35°C.

 

For most enzyme reactions, Q10 is about 2, i.e. for every 10°C rise in temperature, the reaction rate doubles. If the reaction above was kept at 35°C for a long period of time, and then Q10 was calculated, it would appear to be a lot lower than 2. This is because some the enzymes have been de-natured.

As the reaction proceeds, the level of substrate would fall as it is converted into product by the enzyme. As the rate of reaction is also dependent on the concentration of substrate, this too would 'fall and has nothing to do with the effect of temperature. Hence the need for controls, i.e. keep all experimental factors constant except for the one being investigated.

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After a certain point, the rate of reaction begins to fall drastically – at about 60°C, when you might think things should really be moving, there is no reaction at all. Why not? The answer lies in the fact that all enzymes are proteins. As with other proteins an enzyme has a very specific shape, and is held in this shape by strong disulphide bridges and much weaker hydrogen bonds, ionic interactions, etc. Heating the enzymes above a certain level will provide enough energy to break these weaker bonds and unfold the amino acid chain. When this happens the ...

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