A investigation into the effect of inhibitor concentration on the enzyme catalase.

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A Investigation into the Effect of Inhibitor Concentration on the Enzyme Catalase

Aim: To investigate how the concentration of inhibitor (lead nitrate) affects the rate of reaction of the enzyme Catalase.

Hypothesis: In my hypothesis I state that Hydrogen Peroxide (H O ) will breakdown to oxygen and water in the presence of catalase from the potato. The rate of reaction will decrease with increasing inhibitor (lead nitrate) concentration when molecules of Hydrogen Peroxide are freely available. However, when molecules of the inhibitor are in short supply, the increase in the rate of reaction is limited and therefore will have little affect.

Predicted Graph:

Background Knowledge: Enzymes- Enzymes are complex 3-D globular proteins, some of which have other associated molecules. Enzymes are catalysts which alters the rate of chemical reaction without itself undergoing a permanent change, and therefore can be used over and over again.

Enzymes help reactions speed up which would otherwise take place very slowly.

While the enzyme molecule is relatively larger than the larger than the substrate molecule it acts upon, only a small part of the enzyme molecule actually comes into contact. This region is called the ACTIVE SITE. The active site of an enzyme is the region that binds the substrate and contributes the amino acid residues that directly participate in the making and breaking of chemical bonds. However, all enzymes operate only on a specific shape and therefore fits only complementary locks, so only substrates of a particular shape will fit the active site of an enzyme.

Substrate Concentration- For a given amount of enzyme, the rate of an enzyme controlled reaction increases with increasing substrate concentration-up to a point. At low substrate concentrations, the active sites of the enzyme molecules are not all used- there simply are not enough substrate molecules to occupy them all. As the substrate concentration increases, more and more sites come into use. A point is reached, however, where all sites are being used.    

Inhibition- The rate of enzyme controlled reactions may be decreased by the presence of inhibitors. There are two types: Reversible inhibitors and Non-reversible inhibitors.

Reversible inhibitors: The effect of this type of inhibitor is temporary and causes no permanent damage to the enzymes because the association of the inhibitor with the enzyme is a loose one and it can easily be removed. Removal of the inhibitor restores the activity of the enzyme to normal. This also consists of two types: Competitive Inhibitor- These compete with the substrate for the active sites of enzyme molecule. The inhibitor may have a structure that permits it to combine with the active site. While it remains bound to the active site, it prevents a substrate molecule from occupying that site and so reduces the rate of reaction. The same quantity of product is formed, because the substrate continues to use any enzyme molecules that are unaffected by the inhibitor. It does however take longer to make the products. If the concentration of the substrate is increased less inhibition occurs. This is because as the substrate and inhibitor are in direct competition, the grater the proportion of substrate molecules the greater their chance of finding the active sites leaving fewer to be occupied by the inhibitor.

Non-competitive inhibitors- These attach themselves not to the active site of the enzyme but elsewhere on the enzyme molecule. They alter the shape of the enzyme molecule in such a way that the active site can no longer properly accommodate the substrate. As the substrate and inhibitor molecule attach to different parts of the enzyme, they are not competing for the same sites. An increase in substrate concentration will therefore not reduce the effect of inhibitor.

Non-Reversible Inhibitors- This leaves the enzyme permanently damaged and so unable to carry out its catalytic function.

Catalase- This is an enzyme found in food such as potato and liver. It is used for removing Hydrogen Peroxide from cells. Hydrogen Peroxide is the poisonous by-product of metabolism. It speeds up the decomposition of hydrogen Peroxide into oxygen and water. It is able to do this because the shape of its active site matches the shape of Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is an ANABOLIC REACTION.

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Key variable of my experiment: This is the main factor and it will be controlled into each inhibitor change in order to carry out the experiment successfully.

In relation to this another factor that will change will be water concentration to make my inhibitor into a solution, as iron reacts better in this state. However, this will be done proportionally to make 100% solution each time, which is equal to 10cm.

These two will be the only factors that can be varies as all other factors need to remain constant to produce a fair test with accurate ...

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