Breakdown Of Hydrogen Peroxyde Aim Biology Essay

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Background

Enzymes are proteins that catalyze chemical reactions of other substances without them being destroyed or altered upon completion of the reactions. Enzymes are proteins that are produced by living cells that accelerate or catalyze the metabolic processes of an organism (like catalase speeds up the decomposition of Hydrogen Peroxide into water and oxygen, one of the reasons for breaking down this hydrogen peroxide is important because if left alone, hydrogen peroxide in the blood can produce free radicals and they can cause damage to different parts of the body).

Enzymes are usually very selective in the molecules that they act upon, called substrates, often reacting with only a single substrate. The substrate binds to the enzyme at a location called the active site just before the reaction catalyzed by the enzyme takes place, we have two theories for this, the first:

The Lock and Key analogy is the specific action of an enzyme with a single substrate. In this analogy, the lock is the enzyme and the key is the substrate. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme). The induced fit theory assumes that the substrate plays a role in determining the final shape of the enzyme and that the enzyme is partially flexible. This explains why certain compounds can bind to the enzyme but do not react because the enzyme has been distorted too much. Other molecules may be too small to induce the proper alignment and therefore cannot react. Only the proper substrate is capable of inducing the proper alignment of the active site. And the second is the induced fit theory that assumes that the substrate plays a role in determining the final shape of the enzyme and that the enzyme is partially flexible. This explains why certain substrates can bind to the enzyme but do not react because the enzyme has been distorted too much. Other molecules may be too small to induce the proper alignment and therefore cannot react. Only the proper substrate is capable of inducing the proper alignment of the active site.

Reactions take place because the substrates have more energy than the products, but most substrates however need an input of energy for the process to take place which is called 'activation energy'. One catalase enzyme can turn over 40 million molecules of hydrogen peroxide to oxygen and water every second. So the rate of the reaction of an enzyme without any means of activation of energy continues at a faster rate with an appropriate enzyme than without it. The maximum rate of reaction depends on the number of enzyme molecules and the numbers of active sites. There is also some a chemical reaction that synthesize substances which is called anabolic reaction and a catabolic reaction that breaks substances down, these reactions are also know as metabolic reactions.

After the enzyme done its job with the substrate the products leave the site intact and ready to repeat the process with another substrate, but if that same enzyme is affected by a PH that it's not used to it will denature. Many enzymes are sensitive to pH and have a range at which they function most efficiently. Most intracellular function best at or around the neutral pH range and are denatured at either extremely high or low pH (as already mentioned above).

Some enzymes, such as those which act in the human stomach where the pH is very low, will have an appropriately low pH optimum.

Catalase is an enzyme which breaks down hydrogen peroxide into water and oxygen. It does so by way of a "decomposition reaction." Since catalase is an enzyme, it lowers the activation energy, or the amount of energy needed for a reaction to occur. At the same time, it releases energy as it decomposes hydrogen peroxide into its constituents by breaking bonds. Its equation is 2H2O2 in the presence of catalase results in 2 H2O + O2 .

Hypothesis

Both animal and plant cells contain the enzyme catalase which catalyse the breakdown of HP to oxygen and water, liver cells contain more catalase than potato cells, this is because there is a lot more chemical reactions occurring in liver cells that in term is going to produce more HP (which is toxic) this is going to be showed in the results tables.

The investigation is controlled by the consistency of the amount of liver used and the volume of hydrogen and PH, so every time that the experiment is going to be carried out we are going to see the same results.

The reaction to the change in PH was visible by the rate of chemical reaction that was shown by the amount and intensity of the bubbles that were produced.

This investigation will show that the PH level will affect the rate of the reaction of the enzyme catalase on the hydrogen peroxide.

Hydrogen peroxide does not breakdown naturally so catalase will be needed.

Variables

Independent variable was the type of tissue used and the level of PH used.

The dependent variable is the rate of reaction (0 to 3) on hydrogen peroxide.

And the controlled variables were the amount of liver used, the volume of hydrogen peroxide, the sodium hydroxide, the hydrochloric acid and the PH's (11, 9, 7, 4 and 1)

Method

On instruction sheet attached

Results

First Experiment

The following tables will show the rate of reaction when hydrogen peroxide is added to the tissues. (Three tables to compare the results of three groups that did the experiment in class)

Type of tissue

Rate of reaction

observations

Group 1

Group2

Group 3

Animal tissue (liver)

3

3

3

A rapid reaction occurred

Plant tissue (potato)

2

2

2

A moderate reaction occurred

Control (none)

0

0

0

No reaction

Analyses of results for experiment one:

The results show that the animal tissue contains more catalase than the plant tissue, this is proved by the rate of the reaction that was greater than in the plant tissue. In the experiment with the animal tissue when the hydrogen peroxide was applied it was seen a rapid reaction, the oxygen was released in seconds after the application. In the plant tissue a moderate reaction was observed after the hydrogen peroxide was applied a reaction occurred but it was visible that the oxygen was release in lower levels compared to the animal tissue.

Second Experiment

Table showing the effect of different PH on the rate of breakdown of hydrogen peroxide:

Group 1 (Jo's) Group 2 (Margaret's) Group 3 (Linda's)

PH

5 minute observation

Observation when hydrogen peroxide is added

Mean of Results

Group 1

Group 2

Group 3

Group 1

Group 2

Group 3

Group 1

Group 2

Group 3

11

3

3

3

Rapid

Rapid

Rapid

3

3

3

9

3

3

3

Rapid

Rapid

Rapid

3

3

3

7

2

2

2

Moderate

Moderate

Moderate

2

2

2

4

1

1

1

Very slow

Very slow

Very slow

1

1

1

1

0

0

0

None

None

None

0

0

0

Analyses of results for experiment two:

This experiment showed that the optimum PH for catalase is PH11 and PH9 because when other P.H is used the catalase doesn't react as well as it did with its optimum P.H. (As seen in the above table).

When it is not the optimum PH, the substrate shape at the active site is been altered as the hydrogen bonds have been denatured so no reaction is showed.

Breaking up the liver will give a higher reaction, due to the fact that the product has been more exposed to the enzymes.

Evaluation

The procedure was suitable for the experiment as the results were clear.

There were no anomalous results.

The measurement of the liver and PH used was accurate so there was not sources of error which may have occurred had the measurements not been precise.

A strength of the experiment is that the procedure can be easily repeated and replicated.

Some of the faults in the procedure was that the temperature was not controlled and the amounts of tissue used were not precisely cut so it is very difficult to do precise results. Some ways to improve the procedure would be to ensure that the temperate of the water was controlled using a thermostatically controlled water bath, and using potato and liver already mashed to facilitate the experiment and the measurement of the mass of the tissues and to measure them precisely. Some sources of error can be: Scale not been calibrated and zeroed before the experiment, to always use a clean PH strip to check acidity before and not after the procedure and also to check all the agents (if they have the correct PH before the experiment can be carried out).

Conclusion

The investigation concluded that both animal and plant cells contain the enzyme catalase.

Liver cells contain more catalase than potato cells, it was proved by the rate of reaction in the experiments, the higher rate the more catalase the tissue contains.

Liver cells need a higher concentration to make sure that the HP is breakdown

The optimum PH for catalase was PH11 and PH9. The lowest was PH1, which caused the produce to denature. The hydrogen peroxide is used on its own as a control substance.

In the first experiment to test for the presence of oxygen a glowing splint was used in which it re lighted proving the existence of oxygen.

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