This is an experiment to show how different concentration of celery tissue enzyme, catalase breakdown the bonds of hydrogen peroxide, substrate, to produce oxygen given out at different rate of reactions.

Biology coursework

Aim: -

Planning

Background research:-

Catalyst:

Catalyst is a substance that speeds up the chemical reactions, without it self being consumed by the process. Any such process is called catalysis. In industries, catalysts are used to speed up many chemical reactions that otherwise will take place too slowly to be practical.

Enzymes:

Enzymes are proteins. Like other proteins, enzymes consist of long chains of amino acids held together by peptide bonds. Enzymes take part in the breakdown of food materials into simpler compounds. They are also called biological catalyst. This means that by their mere presence, and without being consumed in the process, enzymes can speed up chemical processes that would otherwise run very slowly, if at all. Enzymes are normally named after the reactions they catalyse because their molecular structure is very complex and in many cases unknown. For example, super oxide dismutase is the enzyme responsible for the destruction of the super oxide ion in living organisms.

Enzymes are specific. Contrary to inorganic catalysts such as acids, bases, metals and metal oxides, enzymes are very specific. In other words, each enzyme can break down or synthesize one particular compound. In some cases, they limit their action to specific bonds in the compounds with which they react. Most proteases, for instance, can break down several types of protein, but in each protein molecule only certain bonds will be cleaved depending on which enzyme is used.

Enzyme Mechanism:

One of the unique things about enzymes is that they have one function and one function only. This is to reduce the activation energy. Every substrate in an organism has its own unique enzyme. The substrate, which is to be transformed, fits the enzyme like a key in a lock. Only when the right enzyme finds the right substrate can biochemical reactions occur. If you are using chemicals as a catalyst, you have to put up with a bundle of side effects because chemicals are non-specific. The chemicals will do their tasks to whatever they come across. When an enzyme does the job, there are no side effects. Take the table on the next page as an example showing, which enzymes work on which particular substrate.

Enzymes bind their substrates at active sites. The active site is the location on the surface of the enzyme where the catalysed reaction takes place.

Enzymes are specific just like lock and key, they have exactly the Right shape to fit onto their substrates in just the same way a key fits into the locks. When the enzyme and its substrate molecule lock together, it makes the bond with the substrate molecule and chemically changes it into the products. This is called enzyme-substrate complex.

At the end, the enzyme and product molecules cleave apart allowing the enzyme molecule unaltered to bind onto some other substrate molecule.

The normal equation of how enzymes work is:

E + S = ES = E+P

In this equation E denotes to enzymes, S is the substrate, ES is the enzyme substrate complex and P is the product.

Induced fit hypothesis:-

In this hypothesis, the substrate does not simply bind with the active site. It has to bring about changes to the shape of the active site to activate the enzyme and make the reaction possible. So small molecules may enter the active site, but they cannot induce the changes in shape to make the enzyme behave like a catalyst. The hypothesis suggests that when the enzyme's active site comes into contact with the right substrate, the active site slightly changes or moulds itself around the substrate for an effective fit. This shape adjustment triggers catalysis and helps to explain why enzymes only catalyse specific reactions.

A+B Reactants

C+D Products

Each enzyme can catalyse the forward and reverse reactions equally. Every reaction has to reach an equilibrium point, so that reactants and products stay constant. An enzyme makes the reaction a lot faster. But it doesn’t alter it.

Activation energy is the energy needed to break down the existing bonds and to start a new chemical reaction. The rate of an enzymatic reaction is strictly dependent on the activation energy of the catalysed reaction. Enzymes catalyse chemical reactions by lowering the activation energy needed for the reaction.

A very small amount of enzyme is needed to catalyse large amount of substrate into products, through their lifetime. The number of substrate molecule turned into products by one molecule of enzyme in a minute is called turn over number.

Here are some turned over number of some enzymes: -

Summary of the properties of an enzyme: -

Enzymes are specific; they can catalyse only one peculiar substrate.
Enzymes are not used-up by the chemical reaction they catalyse.
An enzyme makes a bond with substrates to make enzyme-substrate complexes.
Enzymes make the reactions lot faster by reducing activation energy.
Each enzyme has it’s own turnover number.

As enzymes are protein these factors may affect its activity: -

PH
Temperature
Enzyme concentration
Substrate concentration
Cofactors
Inhibitors

Temperature: -

Enzymes will do their job over the range of temperatures prevalent in the cell environment. For living organisms this is body temperature. If it gets too hot, however, an enzyme may no longer be able to help reactions occur. This is because at higher temperatures the protein molecule that is the enzyme may start to 'unravel' as its bonds break, and its surface may no longer be the correct shape for the substrates to fit.

pH: -

The pH of the cell environment will determine how effectively the enzyme can do its job. Some enzymes (those in the stomach, for example) require an acidic environment in order to work. Others (for example, in the intestine) require conditions that are basic. Each enzyme in an organism has its own pH requirement. If the pH changes, it may no longer be able to facilitate the chemical reactions within the cell.

Enzyme concentration:

Enzyme concentration is one of the factors that highly affect the rate of reaction. As we increase the different concentration of celery tissue enzyme the rate of reaction will also increase, it’s so as there are more enzymes to catalyse the substrate, hydrogen peroxide. More enzymes mean more active sites available for the substrate, which increases the rate of reaction, as the substrates will have more sites to bind to. It will also produce more amount of oxygen in the two minutes, as there will be little left of the substrate.

But as we lower the concentration of enzyme catalyse the rate of reaction will also be low. This is because there is a lot of hydrogen peroxide in contrast with enzymes, as a result of this, the active sites will already be occupied by some other substrate and the other substrates will need to wait for their turn. In this case the rate of reaction will be slower, i.e. low amount of oxygen will be produced.

No matter how much concentration of enzyme is present, the reaction will eventually stop, as at very ...