The effect of substrate concentration on the rate of reaction of the enzyme catalyses.

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Antoine Allen

The effect of substrate concentration on the rate of reaction of the enzyme catalyses.

Aim

        To measure the rate of reaction by looking at the amount of oxygen given off when a yeast culture b is added to different concentrations of hydrogen peroxide.

Background information

An enzyme is a biological catalyst. They speed up the rate of a reaction however they are not affected themselves whilst doing this, this is why they are catalysts. Enzymes are made to be specific, this means that they can have only one substrate that they will work on. Each enzyme has an active site that is where their own specific substrate molecule will fit. Enzymes all work best at an optimum temperature that is usually body temperature at 37C. If the temperature that the enzyme has to work at gets too high, normally 40C it will start to become denatured and therefore no longer work on its substrate as the active site has changed shape. In addition, enzymes usually work best at an optimum pH level, this is normally seven because enzymes are proteins which are damaged by very acidic or very alkaline conditions.

Most reactions work better at higher temperatures, this is because molecules move around much quicker. This makes the molecules have more chance to collide with the substrate. With more collisions, there is more chance of a reaction-taking place. This makes the rate of reaction faster. At 40C the enzyme starts to be damaged, this slows the reaction and by around 60C the enzyme will be completely destroyed.

When these bonds are broken, the enzyme, along with the active site, is deformed, thus deactivating the enzyme. This is know as a denatured enzyme

The lock and key theory

Emil Fischer originated the lock and key theory in 1894. It states that it takes the correct key to open a lock. It takes a correct enzyme to bond to the substrate and catalyse its reaction. An active site of an enzyme is made up of a binding site and a catalytic site.

This theory had some bad points and was not correct so in 1958, Koshland said that the shape of an active site of an enzyme does not have to be the same type of the substrate. This was called the Induced Fit Theory.

Active site

It is a depression in the surface of the enzyme. It is complimentary to that specific substrate

Catalyse is an enzyme found in food such as potato and liver. It is used for removing Hydrogen Peroxide from the cells. Catalyse speeds up the decomposition of Hydrogen Peroxide into water and oxygen. It is able to speed up the decomposition of Hydrogen Peroxide because of the shape of the Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction.

As there are, only two substances there will not be competitive inhibition.

Formula:

                       Catalyse

 Hydrogen Peroxide---------------------->Water + Oxygen

                       Catalyse

             2H2O2------------------->2H2O+O2

It is able to speed up the decomposition of Hydrogen Peroxide because the shape of its active site matches the shape of the Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called a catabolic reaction.

The dictionary defines catabolic as the metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy.

The Collision Theory
In order for a reaction to take place, the reacting substances must collide and energy, called the activation energy, must be reached. If the collision between the particles can produce a lot of energy, then a reaction can take place. For the collision to take place, the particles must collide fast enough and in the right direction. The higher the number of collisions, the faster the rate of reaction. Increasing the temperature of the substrate can increase the number of collisions.


Kinetic Theory
The kinetic theory is a theory, which emphasises on pressure, volume, and temperature. It states that gases contain particles that are always moving. Gases then exert pressure because their particles are colliding with the wall of the container. If the volume of the gas is decreased, then the particles would hit the wall more often and the pressure would increase.
When a lump of dough, which contains air and carbon dioxide, is heated in the oven, the volumes of the gases increase, resulting in the bread rising. This process can be shown by this word equation:

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Increase in temperature Volume increases (Gas expands)

This is because as the temperature of the gas increases, the particles get more energy. This causes the particles to move faster and collide with each other and the walls of the container. If the gas cannot expand, the pressure would increase. If the pressure is kept constant while the temperature is increased, then the gas will expand.

Plan

I have planned to experiment I will take a yeast culture solution (enzyme) 3ml, and mix it with 20ml of hydrogen peroxide (substrate), the substrate will be between 4 vol. and 14 vol. Accurately ...

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