An Investigation to See How Much Oxygen Is Given off When Different Concentrations of Catalase Are Added with Hydrogen Peroxide.

An investigation to see how much oxygen is given off when different concentrations of catalase are added with hydrogen peroxide.

Aim: To see if changing the concentration of catalase (found in celery) with hydrogen peroxide affects the amount of oxygen given of.

Background Information: (Hydrogen peroxide - H2O2 1/2O2+H2O)

Enzymes:

Hundreds of chemical reactions happen simultaneously inside living cells and it's the job of enzymes to control and regulate the various metabolic activities. Enzymes are biochemical catalysts, which speed up reactions that would otherwise be too slow to be of any use to an organism. They control cell metabolism by regulating how and when reactions occur. Enzymes are globular proteins; they have complex structures in which the polypeptides of which they are composed show tertiary and often quaternary folding. The three dimensional shape of the protein is vital to its functioning. If altered, they will no longer be able to bind to the substrate (the molecule taking part in the reaction). Their shape is held in place by hydrogen bonds and ionic forces; these can be altered by changes in pH and temperature.

In general enzymes;

1. Are specific (only catalyse one reaction)

2. Join with substrates to form enzyme-substrate complexes

3. Can be used again and again

4. Are sensitive to changes in temperature and pH out of the range in which they normally function

5. Often need other chemicals (co-factors) in order to work

6. Can be slowed down or stopped by inhibitors.

When controlling a reaction, enzymes 'hold' the substrate in place, positioning it at the correct angle, changing its overall charge, causing the enzyme to lower the activation energy of the reaction. The substrate molecule fits into the active site and is held there until the reaction is complete. There are two main theories to describe how this enzyme-substrate complex is formed:

1. The Lock and Key hypothesis - this assumes there is an area on the enzyme known as the active site. This is an area into which the substrate molecule fits. The size, shape and chemical nature of the active site matches exactly to a specific substrate so they fit together like a key fitting into a lock.

2. The Induced Fit hypothesis - this model suggests that the active site is not an exact fit to the substrate but rather moulds itself round it as the complex is formed. When the enzyme is bound to the substrate, the active site becomes able to catalyze the reaction. As products are made, they fit the active site less well and fall away from it.

(An enzyme molecule is very large but only a small part of it, the active site, is involved in the reaction.)

http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookEnzym.html

Active Site:

Enzymes work by having an active site, into which their substrate fits. When the substrate goes into the active site, forming an enzyme-substrate complex, this triggers the reaction to take place.

For example, a hydrogen peroxide molecule (substrate) fits into an active site in the catalase molecule (enzyme), and this causes the hydrogen peroxide to break down into water and oxygen.

Further research into enzymes has shown that the lock and key hypothesis, or model, does not always explain the whole story. Small molecules, such as water, could enter the 'lock' site and interfere with or take part in the reaction.

Human Biology for AS Mary Jones and Geoff Jones

Rate of reactions:

This reaction between enzyme and substrate depends on random movements of molecules. If the molecules happen to collide, and if they have enough energy, then they react. The higher the concentration of enzyme, the more likely it is that the molecules will collide, and so the faster the reaction goes. This could be represented by a straight-line graph of rate of reaction against enzyme concentration.

In theory, if the concentration of enzyme is very high indeed, all of the substrate molecules will be converted instantly, and the rate of reaction will then have reached a maximum. However, in practice, the concentration of enzyme is normally much lower than that of the substrate - and this maximum is never reached.

Substrates fit into the active site, one at a time. The rate of reaction will increase but eventually it will level off because all the active sites are filled.

Increase the substrate concentration and the rate of reaction will increase. The substrate concentration is described as limiting the rate of reaction.

When the substrate concentration increases the rate of reaction no longer increases. Something else is limiting the rate of reaction. It is probably the enzyme concentration

Human Biology for AS Mary Jones and Geoff Jones

Inhibitors:

Non-competitive inhibitors do not have the same shape as the substrate and therefore do not compete for the active site.

Non-competitive inhibitors bind at the same other point on the enzyme molecule. This changes the shape of the active site so an enzyme-substrate complex cannot be formed.

Competitive inhibitors have similar shapes to the substrate and therefore fit into the active site of the enzyme.

They don't take part in the reaction. These inhibitors block the active site so the substrate can't enter.

Because the inhibitor is competing with the substrate for the active site, it is sometimes called a competitive inhibitor' because this is part of the enzyme it effects.

(http://www.bbc.co.uk/education/asguru/biology/intro.shtml)

Hypothesis: As the concentration of the catalase (from the celery) increases the amount of oxygen given of in two minutes will also increase. I have chosen this for my hypothesis because in my background information I have found evidence showing that if the concentration of the enzyme