AN INVESTIGATION TO DETERMINE THE EFFECT OF ALTERING THE CONCENTRATION OF HYDROGEN PEROXIDE ON THE RATE OF REACTION OF THE ENZYME CATALASE.

A-Level: Biology

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Catalase is an enzyme, made from protein molecules and is found in every cell that respires aerobically. The quantity of catalase varies according to the amount of the substrate produced.
Catalase is one of the most distinctive group of enzyme that can be oxidize and reduce hydrogen peroxide.
It is thought that catalase can repeat it’s reaction over few millions times per second, as it has four active sites, therefore catalase is vital for survival in all organisms.
In this investigation, the role of the catalase is to break down Hydrogen Peroxide, otherwise known as an anabolic reaction. Hydrogen Peroxide is a product of most metabolic reactions carried out within living cells; therefore catalase is needed as a defensive enzyme.
For this investigation the source of catalase will be activated yeast solution which contains dried yeast and glucose. The solution is made up 30 minutes before the start of the investigation to allow the intercellular enzymes to become active.
Hydrogen peroxide is unstable and breaks down readily into water and single oxygen. Oxygen is only stable when it is in diatomic state, single oxygen molecules are a strong oxidizing and reducing agent hence making it poisonous. Hydrogen peroxide is an effective yet simple substance, that even our immune system produces and uses it to control bacteria and viruses.


(HYDROGEN PEROXIDE) (WATER) (OXYGEN)
2H2O2 2H2O + O2

The equation above shows the decomposition of Hydrogen Peroxide in the company of catalase. This is an EXOTHERMIC REACTION.
Hydrogen Peroxide is liberally miscible in water and is able to cross fluid cell surface membranes readily. It is thought that Hydrogen Peroxide is very toxic in vivo and must be hastily eliminated, thus the need of catalase.
The danger of Hydrogen Peroxide largely comes from its ready conversion to the haphazardly reactive hydroxyl radical. One danger is the exposure to UV light and the other danger is the interaction of hydrogen peroxide and a series of the transition metals, of which the most important is iron, found in the majority of human cells. High amount of iron can cause hydrogen peroxide repel form catalase.
The amount of hydrogen peroxide varies between every cell but however hydrogen peroxide is poorly reactive, it can act either a mild reducing or oxidizing agent, but it does not oxidize readily with most biological molecules such as lipids, DNA and proteins.

Enzymes are soluble globular proteins with a specific shape and therefore specific in reactions they catalyse. This reaction occurs on a surface known as the active site where the substrate momentarily binds with the enzyme to form an enzyme-substrate complex. Bonds can then be formed or destroyed and the products are released.
As active sites for all enzyme of the same type, will have the same arrangement of amino acids, the enzyme will only catalyse a specific reaction where only one type of substrate molecule will fit. This is known as the lock and key theory, where the active site complements the substrate. This is shown below.

There are certain factors that could affect the rate of reaction in the decomposition of hydrogen peroxide are things such as temperature, pH and enzyme concentration and also substrate concentration as well as inhibitors.
Enzymes have an optimum temperature, at which they work best. For mammalian enzymes this is about 37°-40°.
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