Investigating the action of the enzyme Catalase upon hydrogen Peroxide

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Investigating the action of the enzyme Catalase upon hydrogen Peroxide

Aim
Effect of temperature of the action of the Enzyme Catalase.

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 Metabolic reactions occur quickly and thousands of reactions are taking place at the same time in cells. Order and control is essential if reactions are not to interfere with each other. These features of metabolism are made possible by the action of enzymes. For centuries humans have used enzymes to produce bread, cheese, yoghurt, wine and beer. But now they are used on a wide commercial scale in the pharmaceutical and agrochemical industries and for analytical purposes.

Enzymes have the following properties:

•They are large protein molecules   

•act as catalysts

•lower activation energy

•Are reversible in their action

•Are very efficient, having high turnover numbers

•Can be detected by heat

•Most are specific.

How enzymes work- Enzymes work with another molecule called a substrate. Each enzyme has its own special shape, with an area (the active site) on to which the substrate molecules bind (see diagram below)

Modern interpretation of the lock and key method theory suggest that in the presence of the substrate the active site may change in order to select the substrate’s shape. This is called the induced fit hypothesis.

 Catalase is an enzyme capable of converting hydrogen peroxide into water and oxygen by the following reaction:

2 H202 ---Catalase Enzyme---> 2 H20 + 02

Like other enzymes, catalase is simply a reaction catalyst; it helps the reaction reach completion without adding or removing molecules.  The exact method of conversion is not completely understood although many catalases have been sequenced and their secondary and tertiary structures are known.   Catalase is present in many bacteria.

What affects Enzymes?

• Temperature - Enzymes will work faster and faster as the temperature increases. The kinetic theory explains why the rate of chemical reactions will increase with temperature. As the temperature increases the movement of reactant molecules also increases leading to more successful collisions which result in reactions. Studies have led to a general rule of thumb which says that the rate of a reaction doubles for each 10 degree Celsius rise in temperature.  However once they reach a certain temperature then they will stop working. Around the higher temperature usually around 45˚c enzyme denaturation will decrease the reaction rate significantly. Their optimum PH is often around 37˚c, which also happens to be the temperature of the body. At very low temperatures e.g. freezing, enzymes work very slowly.

• PH - They work best in neutral conditions neither acidic nor alkaline. Individual enzymes have a very narrow optimum range.

•Inhibitors –The rate of enzyme controlled reactions may be decreased by the presence of inhibitors. There are two main types of inhibition: reversible and non-reversible. Reversible inhibition is where the effect of the inhibition is temporary. There is no permanent damage to the enzyme because the association of the inhibitor with the enzyme is a loose one. Removal of the inhibitor allows the enzyme to function normally. There are two types of reversible inhibitor8s: Competitive, where the inhibitors structurally similar to the substrate. The more substrate molecules the greater the chance of finding active sites. This leaves fewer to be occupied by the inhibitor.

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Non competitive is where the inhibitor has no resemblance to the substrate molecule and binds to the enzyme at a site away from the active site. The rate of reaction is therefore unaffected by the substrate concentration.

Non reversible inhibition is where it leaves the enzyme permanently damaged, e.g. mercury breaks the disulphide bonds which maintain the shape of the enzyme molecule.

•Substrate concentration – The michealis constant is the concentration of substrate needed to make the reaction proceed at half its maximum rate. A low michealis constant means that the reaction proceeds rapidly ...

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