Investigation of the breakdown of Hydrogen Peroxide by enzymes in living tissue

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Philippa Brook 11SP

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Investigation of the breakdown of Hydrogen Peroxide by enzymes in living tissue

Plan and Research

I am going to investigate the rate of reaction between enzymes in potato cells and them breaking down Hydrogen Peroxide, also looking at the effect temperature has on the experiment.

Enzymes are present in all cells (usually the mitochondria) of living things.  Catalase is the name of the main enzyme found in cells, depending on the tissue and which area of the ‘body’ it comes from determines how many enzymes are present (and in what concentration).

Hydrogen peroxide (H2O2) is very unstable and will decompose breakdown slowly on its own, into water and oxygen, however a catalyst will speed up this reaction.  Enzymes are catalysts; a catalyst alters the rate of a reaction, usually speeding it up.  Catalyst are also not used up in a reaction, so can theoretically be used over and over again.  They use a ‘lock and key’ method to breakdown or build up.  Different enzymes are designed to work with different substrates.  Catalase can be used to break down hydrogen peroxide, that is why it will be Catalase in the potato cells that will be breaking down the hydrogen peroxide.  The equation for this is:

Catalase

2H2O2                  H2 O + O2

Catalase

Hydrogen Peroxide                      pure water + oxygen

The reason Catalase can be used as a catalyst in this reaction is because Catalase is made up of amino acids (proteins) as all enzymes are; it also has a cofactor from the haem group.  A cofactor is an addition to the individual enzyme.  Which isn’t made out of protein and helps in the breakdown of substrate (hydrogen peroxide in this case).  A cofactor from the Haem group means it contains iron, as haemoglobin does.  Iron and oxygen react well together, that is why Catalase can be used as a catalyst for my experiment.  So in theory I could use just use iron as a catalyst as well.

Sometimes cofactors aren’t really attached to the enzyme but are really an extra substrate; they are usually something useful within the cell.

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In my experiment I will be looking at temperature and how it affects the rate in the reaction.  Enzymes work best at their optimum temperature, if the temperature goes above this the enzymes begin to denature.  When an enzyme denatures it is because the heat can disrupt the bonds in the proteins primary, secondary and tertiary structures, by causing the atoms to vibrate out of shape from an increase in energy.  The heat causes this.  Once the enzymes are vibrating the ‘lock and key’ method will not work until the enzymes are cooled enough to stop vibrating.  If the ...

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