'Investigating how temperature affects the rate action of the amylase enzyme on starch.'

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Maytham Aomran        Page ___        Practical Investigation 1

19/11/2001                Amylase Enzyme

Investigating Enzymes

Aim: ‘Investigating how temperature affects the rate action of the amylase enzyme on starch.’

Background Reading

Before conduction of both preliminary and the official investigations, I did research on enzymes, their structures and properties both during school and at home dependently using the internet, varies software and books ( / Encarta encyclopaedia / School Biology book). This Investigation should hopefully reinforce my understanding of enzymes and particularly the Amylase Enzyme. I have decided to express the knowledge not in this section but throughout this essay in major areas such as the prediction.

Hypothesis:

I hypothesise; using my scientific knowledge of enzymes from the essential background reading that increasing the temperature will increase the rate of reaction between the enzyme and the substrate accordingly.

However, I am aware that the temperature can only be increased or decreased to a certain point before the reaction corrupts as the enzyme will cease to function. I believe that this will occur at above 45°C i.e. optimum temperature.

Prediction:

(Theory part of this applies to both the Preliminary and Official Experiment)

The focal factor which has been assigned to this investigation is temperature. This Investigation will look at how the temperature affects the rate at which a bacterial amylase enzyme works upon a starch solution.

Enzymes are a chain of amino acid polymers and are produced in living cells. They often act as biological catalysts and so catalyse (speed up) a reaction (a catalyst is a chemical substance which speeds up a reaction but does not get used up during it). 

For example, if starch is mixed with water it will break down very slowly into maltose, taking several years, however, in your saliva there is an enzyme called amylase which can break down starch to glucose in minutes or seconds.

So as can be seen, water alone can react with the starch and digest it. In fact the majority of chemical reactions in the body require water. That’s why we can not live long without it. Amylase enzyme merely speeds up the reaction significantly; otherwise as stated earlier will take several years with only water. This is the main purpose of enzymes.

Certain variables affect the rate at which these biological catalysts function. Some variables could increase their rate, decrease their rate or just stop them functioning completely. Though, this investigation assigns temperature as the key variable to find out how it alters the rate of reaction between the amylase and the starch solution. As was stated in the hypothesis on page 1, increasing the temperature will increase the rate of reaction between the enzyme and substrate. (However, the temperature will have limit to being increased whilst being beneficial to the reaction)

Explaining the Prediction:

This is mainly obvious if we incorporate knowledge from the other areas in science, namely the Kinetic theory. Increasing the temperature will transfer energy to the particles causing increased movement (as they are both in the liquid state and so will be moving/colliding particles). Accordingly, as the temperature continues to increase then more and more energy is transferred to the particles and so therefore the velocity of the particles will continue to increase further. If the amylase and starch particles are at a greater speed, then there is going to be more collisions taking place in a given time. If they are going to be more collisions, then the chances of an effective collision will also increase. Thus, temperature is beneficial to reaction as the reaction will take place at an increased rate.

Effective Collision: 

For a chemical reaction to occur, the reacting particles must collide. There must be enough energy available firstly to break the original bonds and then enough energy to make new bonds with the other reactant molecules. If this is not such, the reactant molecules will simply bounce of each other. Though, if there is sufficient energy available to collide with other reactant molecules and then bind with them, this is will be an effective collision and so will result in a reaction.

As a brief conclusion, the temperature provides significant energy to the particles. This energy not only increases their chances of colliding but in assuring the collision is an effective collision and so will result in reactants binding (reacting).

So why does this variable (temperature) have a limit to being beneficial in the reaction?

>>Before explaining the necessity of controlling the temperature in the reaction (i.e. too high or too low), an enzyme’s structural properties must be taken into consideration.

An enzyme has a surface, which contains a cavity known as an active site. Reactant molecules become ‘trapped’ into this active site and so collide more frequently resulting in more collisions and so a greater rate of reaction i.e. the main purpose of an enzyme.

Enzymes are commonly exemplified by the popular ‘Key and Lock’ system. Basically, the enzyme acts as a lock which has a unique shape i.e. the active site of which only the correct key can fit in. This key is the substrate. No other substrate can fit into this active site. This is why enzymes are ‘specific’; they work only on one type of substrate. We have many enzymes in our body; however, we do not have an enzyme for roughage (fibre). Another enzyme like amylase cannot simply be used to digest it as the roughage ‘key’ cannot fit into the amylase ‘lock’ (active site)

Regarding the above question:                                                                The temperature is beneficial to the enzyme by increasing the rate of reaction, though only up to a certain temperature! As was stated before, we know that enzymes are all long folded chains of a protein molecule. Thus, when increasing the temperature this folded chain jostles and reforms and so the changes the shape of the active site.

The Enzyme has a range called the ‘Optimum Temperature’. The optimum temperature(s) is where the enzyme functions most rapidly. Therefore, as the temperature continues to increase above the optimum temperature (and vice versa) it begins to change shape until a point is reached where the active site has changed so much it can no longer be able to ‘trap’ the reactants. The substrate cannot fit into it. This is the point where the enzyme is said to be denatured.

Obviously this a major drawback, as now the enzyme can no longer increase the rate of digesting starch.

This is an irreversible process. That means if you were to increase it greatly above the optimum temperature then the ‘lock’ (active site) will have changed so much the ‘key’ (substrate) will not be able to fit in! So even if you were to decrease the temperature back to the optimum, the enzyme will still have that rearranged ‘lock’ (active site) and so the ‘key’ (substrate) will not be able to fit in. This is what is meant by denatured; however, not dead as enzymes are not living organisms.

Diagram representing how Amylase breaks down Starch:

Here are diagrams I drew to show a ‘representation’ of how Starch (made up of 4 Glucose molecules) is broken down into Maltose (2 Glucose molecules) by the aid of the Amylase enzyme. These are just shapes to represent the ‘key and lock’ system of the enzyme and substrate.

Below shows the starch Molecule is depreciated on the Amylase Enzyme to be broken down.

Finally, I have shown here the break up of the Starch molecule into a Maltose Molecule (The salivary gland does this process in the mouth)

 I have looked at what an enzyme is, what its main functions are and how this is linked with their structural properties. I have looked at how my assigned variable, temperature, has affected the rate at which an enzyme works and in particular I have regarded the enzyme I am investigating, amylase enzyme. I have stated a hypothesis prior to my investigation due to the some research, and have explained the reason. I finally have drawn a clear diagram to show how amylase would digest starch.

Having done all of that. I am aware that there are other variables that could also affect the rate of enzymes. This is not part of my investigation, but I have chosen to mention these variables as they will be crucial in the latter ‘fair testing’ part of my investigation.

Variables that affect the rate of enzymes:

  • Ph of Amylase-Starch solution:

This Variable can be tested using such chemicals as Hydrochloric Acid (Acid) and Sodium Hydroxide (Alkaline) and be mixed to obtain a desired Ph quantity. Like temperature, an enzyme also has an “Optimum Ph Range.” As I will not be conducting this variable therefore not alter the Ph.

Variables that affect the rate of enzymes:

For both Preliminary and Official experiments

  • Concentration of Starch:

When increasing the concentration of Starch you are really adding more starch particles in a given volume. This can be achieved by adding more starch solution. If there are more starch particles then obviously there is going to be more collisions with the amylase enzyme in a given time. If there are going to be more collisions, then there will be more effective collisions and so a greater rate of reaction.  Diffusion is a good example; sugar would dissolve faster in higher concentration of a solute such as water. This is because more water particles are available and so will be colliding more frequently. Hence, it will dissolve much faster. This I picked up from my lessons on the Brownian motion. (I will be using 5ml Starch)

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  • Concentration of Enzyme:

Likewise, the variable affects the reaction in the exact same as that with the starch concentration. (I will be using 1ml amylase enzyme)

  • State of Starch

To identify how this variable affects the rate of the amylase-starch reaction, knowledge of the states of matter must be incorporated.

A liquid would react faster then a solid, this is because there are fewer bonds in the liquid than the solid and so the particles would be more be more free particles and so will be moving more frequently than a solid. If ...

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