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

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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.) 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,...
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