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Discover the affects of PH on the enzyme catalase

Catalase- This is an enzyme found in food such as potato and liver. It is used for removing Hydrogen Peroxide from cells. Hydrogen Peroxide is the poisonous by-product of metabolism.

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It speeds up the decomposition of hydrogen Peroxide into oxygen and water. It is able to do this because the shape of its active site matches the shape of Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is an ANABOLIC REACTION.

BACKGROUND INFORMATION ON ENZYMES:

Enzymes- Enzymes are complex 3-D globular proteins, some of which have other associated molecules. Enzymes are a catalyst which alters the rate of chemical reaction without itself undergoing a permanent change, and therefore can be used over and over again.

Enzymes help reactions speed up which would otherwise take place very slowly.

While the enzyme molecule is relatively larger than the larger than the substrate molecule it acts upon, only a small part of the enzyme molecule actually comes into contact. This region is called the ACTIVE SITE. The active site of an enzyme is the region that binds the substrate and contributes the amino acid residues that directly participate in the making and breaking of chemical bonds. However, all enzymes operate only on a specific shape and therefore fit only complementary locks, so only substrates of a particular shape will fit the active site of an enzyme.

Prediction

I predict that as the PH increases the activity of enzyme increases until the optimum PH is reached. Catalase optimum ph is around 6-7.after that the enzyme will be denatured.

Hypothesis

The enzyme will have an optimum pH of around neutral. Either side of the optimum pH will have relatively high rates of reaction or far away from the optimum pH will have a low rate of reaction. The enzyme catalase is found in many tissues including potato and liver. It is important because it breaks down the hydrogen peroxide formed in metabolism. Hydrogen peroxide is toxic and if it were not broken down it would kill the cells. As it does this, it liberates carbon dioxide that can be collected.

CHEMICAL EQUATION:

2H2O2 ——————-> 2H2O + O2

I also hypothesize that the catalase activity will be highest with the sample of potato comparing to the apple.

Variables

The factors, which will have an affect on the enzyme activity, will be:

* Temperature

* Concentration of enzymes

* pH

The variable in which I will be using to investigate the enzyme activity is the temperature. The rest of the variables will be kept constant and only the temperatures will be changed.

Apparatus

To test how the PH affects the rate of reaction, I will use the following apparatus:

* Gas syringe through bung

* Potato

* Hydrogen Peroxide

* Stop Clock

* Cork borer

* Scalpel

* water Beaker-250 cm�

* Delivery Tube

* Ph 3,5,7,9

* 5 cm� or 10 cm� plastic syringe with end cut off

* measuring cylinder

* conical flask

* White tile

* wax

* Test tubes

* Test tube rack

* Safety equipment; goggles, lab coat, gloves

Alternative:

Use yeast, broad beans or liver, instead of potato and apple.

Method

1. Measure out 5cm3 of potato into a conical flask

2. Measure out 10 cm3 of buffer solution into a separate container and mix it with minced potato.

3. Measure out 5cm3 volume of hydrogen peroxide in syringe.

4. Fill a tub with water.

5. Completely immerse a measuring cylinder in the water making sure to release all air bubbles in the cylinder and keep underwater.

6. Position the cylinder upright ensuring the open end remains underwater and clamp securely

7. Add the hydrogen peroxide to the potato and place bung on conical flask whilst starting timer.

8. Run experiment for 5 minutes taking readings every 30 seconds by noting the amount of gas at top of cylinder (at meniscus)

9. Repeat the experiment with different ph.

Justification of method:

I have chosen to use this method because it is safe, efficient and accurate. I feel that it will help me to obtain reliable results.

Risk Assessment

* Hydrogen peroxide is a dangerous substance. It can cause serious injury to the eyes and skin. It is therefore necessary that goggles be used for eye protection. In addition, eye irrigation equipment should be readily available in case of an emergency.

* The working area must be clean, tidy and dry. Make sure there is no obstacle in the working area so that you can easily move around as. This allows you to perform the experiment safely and unimpeded care should be taken to ensure that liquid is not spilled onto the floor to cause slippage.

Result table

Time(s)

Oxygen gas collected (cm3)

Ph 3 ph 5 ph7 ph9

30 1.5 1.5 0.5 1.5

60 1.5 3.0 1.5 2.0

90 1.5 5.0 2.0 2.0

120 1.5 7.0 5.65 2.0

150 1.5 8.3 10.3 2.0

180 1.5 9.0 14.35 2.0

210 1.5 10.0 17.35 2.0

240 1.5 11.1 20.15 2.0

270 1.5 13.6 24.15 2.0

300 1.5 14.0 31.15 2.0

These results clarify that the optimum ph for catalase is 7 which supports my prediction. At the lowest ph 3, less oxygen was released, measuring a slower rate of reaction. My background information explains this. The enzyme don’t work as it is neared extreme PHS. This is because its shape would have been change slightly; means the active site may not fit into the substrate any more.

Further investigation:

If this investigation were to be done again, I would take all results myself and use my own interpretation, thus gaining more reliable results. I will know how much potato to measure out for each experiment and also I will make sure that the other variables are kept constant. I have taken the same amount of each, keeping them constant. This would give me clearer results to aid me in my understanding as to how ph can affect the activity of catalase.