Enzymes are biological catalysts made up from protein

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Biology coursework on enzymes

Background Knowledge

Introduction:
Enzymes are biological catalysts made up from protein. As we know, catalysts are substances that speed up the rate of a reaction without itself being used up.
An enzyme has an active site, which has a unique shape into which only a substrate of the exact same unique shape can fit. When this substrate fits into the active site it forms an enzyme-substrate complex:

Enzymes can be denatured at certain conditions. These conditions are high temperatures and extreme levels of pH. The bonds that hold enzymes together are quite weak and so are easily broken by the above conditions. When these bonds are broken the enzyme, along with the active site, is deformed, thus deactivating the enzyme. This is know as a denatured enzyme:


The Effect of Enzyme Concentration:

Rate of Reaction


Enzyme Concentration

The rate of reaction is directly proportional to the enzyme concentration when the substrate is in excess. This is due to the fact that when the enzyme concentration is raised it makes more active sites available to react with the substrate.

The Effect of Substrate Concentration:


Rate of
Reaction


Substrate Concentration

As you can see from the graph, at low substrate concentrations the rate of reaction is directly proportional to the substrate concentration due to the fact that when the substrate concentration is increased the rate of enzyme-substrate collisions (reaction) is equally increased.

However, as the substrate concentration rises the rate of reaction will finally reach a maximum level. This is because all the active sites are saturated with substrate.

The Effect of Temperature:

Optimum Temperature

Rate of
Reaction



0 10 20 30 40 50 60 70 80 90 100
Temperature /°C

At the lower temperatures, the rate of reaction rises with a very steep gradient as the temperature increases (0-36°C). This is because the molecules of the enzyme move faster and faster thus causing the rate of enzyme-substrate collisions to increase. We know that the rate of reaction doubles every 10°C. This can be shown by:
Q10 = 2

The temperature rises to such a degree that the enzyme becomes denatured. This is because the molecules of the enzyme vibrate so violently that they break their weak bonds holding the structure of the enzyme together.

As shown in the graph, the perfect temperature for the majority of enzymes is 37ºC. For this reason, our body temperature is 37°C

The Effect of pH:

Rate of Optimum
Reaction pH

0 3 5 7 9 11 13
pH

With a change of pH the weak bonds holding the enzyme together will break. This will denature the enzyme, thus deactivating the active site. As enzymes normally exist within cells where the pH is 7, the most favourable pH is obviously 7. As you can see from the graph, a pH significantly higher or lower than 7 will kill the cells

Catalyse and Hydrogen Peroxide SC1

Aim:
To investigate the effect of temperature on the enzyme catalase.

Prediction:
Using my existing scientific knowledge, I predict that as I raise the temperature to 30, 35, and 40, this is where we will see the greatest reaction. I predict this because enzymes are designed to react best at the body temperatures of the animals to which they belong. For a mammal, this is around 35-36. Catalysts are used to speed up biochemical reactions in the body.

An enzyme is a protein molecule that speeds up chemical reactions in all living things. Without enzymes, these reactions would occur too slowly or not at all, and no life would be possible. All living cells make enzymes, but enzymes are not alive. Enzyme molecules function by altering other molecules. Enzymes combine with the altered molecules to form a complex molecular structure in which chemical reactions take place. The enzyme, which remains unchanged, then separates from the product of the reaction. Therefore, an enzyme is a sort of biological catalyst. Those enzymes identified now number more than 700.

Enzymes are classified into several broad categories, such as hydrolytic, oxidising, and reducing, depending on the type of reaction they control. Hydrolytic enzymes accelerate reactions in which a substance is broken down into simpler compounds through reaction with water molecules. Oxidising enzymes, known as oxidises, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed.

Catalase is present in the peroxisomes (microbody organelles that house various oxidation reactions in which toxic peroxides are generated as side products) of nearly all aerobic cells. It serves to protect the cell from the toxic effects of hydrogen peroxide by catalysing its decomposition into molecular oxygen and water without the production of free radicals (An atom or a group of atoms with an unpaired electron. Radicals are unusually reactive and are capable of causing a wide range of biological damage)

Hydrogen Peroxide = 2H2O2
Hydrogen Peroxide + Catalase = Oxygen + Water

Apparatus:
Measuring cylinder To hold 100ml of water. This was thoroughly cleaned with tap water beforehand to ensure that the water was not contaminated with anything. This may have led to anomalous results in the long-term.
Clay Beehive To provide somewhere to connect the pipe from the mixture to the water. It also acted as a ledge to hold the measuring cylinder as it stood upside-down.
Tub To hold water and everything in place.
Stopclock To time experiment. I ensured that the experiment was timed as soon as it began because if it hadn't, then the results may have been inaccurate.
Water bath To heat chemicals.
Conical Flask To hold the yeast and hydrogen peroxide solution together once the experiment had begun. This needed to be cleaned using water to ensure that nothing would contaminate the solution.

Diagram:

Method:
I set up the experiment as shown above. I filled the tub full of water. I then placed the beehive in the water. Then I filled a measuring cylinder with exactly 100.0ml of water and placed it on the beehive in the water without letting any of the water in the measuring cylinder escape. I needed it to be exactly 100.0ml so that I could measure it exactly, from a starting point which is relatively easy to remember. After all, 100.0ml is a lot easier to remember than 87.3ml! The measuring cylinder was thoroughly cleaned to ensure as little impurities in the water as I could possibly control. Whilst this was being set up, I had already prepared 40.00ml of yeast and 20.00ml of hydrogen peroxide in separate boiling tubes. At this point, it was very important that I kept the two substances apart because if they had been mixed, they would have begun to react The boiling tubes were both cleaned to ensure the chemicals didn't react with anything, and were as "pure" as possible before the experiment began. When I was certain that it was all prepared, I poured both liquids into a conical flask and fixed on a bung with an attached tube. This operation needed to be practised before the experiment was done for real to ensure it was done as quickly as possible. After all, the hydrogen peroxide and yeast solution will have started reacting as soon as they came into contact. I connected the tube to the clay beehive and measuring cylinder, which were both already prepared in the water. From the very beginning, I started the stopclock timing and noted down how much oxygen had been reacted and had travelled down the pipe into the 100ml of water in the measuring cylinder. I noted down the volume of water that was left in the measuring cylinder after five minutes, taking a result every minute. I chose to take down the result for five minutes because any longer than that and there was none, or barely any water remaining in the measuring cylinder. This is because the yeast and the hydrogen peroxide would have finished reacting completely.

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Variables:
Variable: The temperatures of the hydrogen peroxide and the yeast.

Controlled Variables:
Volume of water in the measuring cylinder: 100.0ml
Times: 0, 1, 2, 3, 4, 5 minutes
Types of liquid: Water, Hydrogen Peroxide, and Yeast solution
Volumes of substances: 40.00ml yeast, 20.00ml hydrogen peroxide
Room temperature: 25ºC approximately
Temperatures of mixture: 20.0?C, 30.0?C, 40.0?C, 50.0?C, and 60.0?C. These must be kept as exactly as possible as yeast is very receptive to changes in temperature.

If these variables were altered, it would not be fair test.

Results:
20.00 20.00 20.00 Avg 30.00 30.00 30.00 Avg
0 100.00 100.00 100.00 0 100.00 100.00 100.00
1 75.00 58.00 66.50 1 41.00 ...

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