Planning Coursework-Starch and Amylase

PLANNING COURSEWORK- STARCH AND AMYLASE

AIM

The aim of this coursework is to investigate the effect of temperature change, on the rate of hydrolysis of starch catalysed by amylase.

PREDICTION

I think that as the temperature increases, the rate of reaction also increases, to a point when it dramatically decreases.

On graph 1, you will see a sketch of the graph which I expect to be the result of the experiment.

SCIENCE REASONING

I think my prediction is correct because the rate of a reaction simply depends on how often and how hard the reacting particles collide with each other.

If the temperature is increased it means there are more particles of reactant knocking about between the water molecules, which make collisions between the important particles more likely.

Enzymes are catalysts and increase the speed of a chemical reaction without themselves undergoing any permanent chemical change. They are neither used up in the reaction nor do they appear as reaction products.

The rate of a reaction increases until all the active site of an enzyme is filled with a substrate or the reaction has reached its maximum rate, or stopped.

The basic enzymatic reaction can be written as follows:

S + E → P + E

SUBSTRATE ENZYME PRODUCT ENZYME

As you can see, when an enzyme is added to a reaction, it reacts with the substrate but also comes back out at the end, it never changes.

The lock and key theory utilizes the concept of an "active site." The concept holds that one particular portion of the enzyme surface has a strong affinity for the substrate. The substrate is held in such a way that its conversion to the reaction products is more favourable. If we consider the enzyme as the lock and the substrate the key, the key is inserted in the lock, is turned, and the door is opened and the reaction proceeds. However, when an inhibitor which resembles the substrate is present, it will compete with the substrate for the position in the enzyme lock. When the inhibitor wins, it gains the lock position but is unable to open the lock. Hence, the observed reaction is slowed down because some of the available enzyme sites are occupied by the inhibitor. If a dissimilar substance which does not fit the site is present, the enzyme rejects it, accepts the substrate, and the reaction proceeds normally.

This is an example of competitive inhibition.

Not only enzymes are used to speed up a reaction, but it is also believed that some form of energy is needed for a chemical reaction to occur. This energy is called "the energy of activation". It is the magnitude of the activation energy which determines just how fast the reaction will occur. It is believed that enzymes lower the activation energy for the reaction they are catalysing.

The enzyme is thought to reduce the "path" of the reaction. This shortened path would require less energy for each molecule of substrate converted to product. Given a total amount of available energy, more molecules of substrate would be converted when the enzyme is present (the shortened "path") than when it is absent. Hence, the reaction is said to go faster in a given period of time.

This is a diagram of the concept of energy activation.

EFFECTS OF TEMPERTURE ON ENZYMES

Like most chemical reactions, the rate of an enzyme-catalyzed reaction increases as the temperature is raised. A ten degree Centigrade rise in temperature will increase the activity of most enzymes by 50 to 100%. Variations in reaction temperature as small as 1 or 2 degrees may introduce changes of 10 to 20% in the results. In the case of enzymatic reactions, this is complicated by the fact that many enzymes are adversely affected by high temperatures.

The reaction rate increases with temperature to a maximum level, then abruptly declines with further increase of temperature. Because most animal enzymes rapidly become denatured at temperatures above 40*C, most enzyme determinations are carried out somewhat below that temperature.

Over a period of time, enzymes will be deactivated at even moderate temperatures. Storage of enzymes at 5*C or below is generally the most suitable. Some enzymes lose their activity when frozen.

PRELIMINARY WORK

In pairs, we all did our own experiment to investigate the time course of the hydrolysis of starch to maltose, catalysed by the enzyme amylase.

We measured 0.5cmÑ- of iodine to each of the 12 colorimeter tubes, labelled them 1-12 and then added 5cmÑ- of distilled water to one of the colorimeter tubes, and we used that tube as our blanker for the colorimeter.

We measured 60cmÑ- of starch solution into a beaker, then added 40cmÑ- of amylase, stirred the contents and started the stop clock immediately.

At every 2 minute interval, we removed 5cmÑ- of the mixture and added it one of the colorimeter tubes. We then mixed the mixture and the iodine together, reset the colorimeter with our blanker, and then got the reading of that colorimeter tube. We repeated the experiment until each of the colorimeter tubes had a sample of starch/amylase solution, and recorded it into a results table.

Down below is a table of my results:

Test tube Time (mins) Absorbance

1 2

2 4

3 6

4 8

5 10

6 12

7 14

8 16

9 18

10 20

11 22

With this I can convert absorbance units into concentration of starch units. I can