Enzymes, their activity and their role in the body.

P5 - Demonstrate the factors that affect enzyme activity.

Enzymes are biological catalysts. This means that they are substances with the ability of increasing the rate of chemical reactions without being used up themselves. They are also proteins that are folded into complex shapes (tertiary proteins) allowing smaller molecules to fit into them. The molecules that react with the Enzymes are called “Substrate molecules”. The substrate molecules fit into the “active site” of the enzyme molecules as shown.

This diagram describes the lock and key hypothesis which basically explains that the substrate molecule and enzymes both have particular shapes that allow reactions only with certain molecules. The hypothesis states that the substrate works as a key, and it has a certain shape that will only react with a certain enzyme (lock). If the substrate is not the correct size or shape for the enzyme, a reaction cannot occur between the enzyme and substrate. The induced fit theory assumes that the final shape of the enzyme can be altered slightly to fit different substrates.

The basic role of enzymes in the body is to help with chemical reactions throughout the body by reducing the activation energy needed for reactions to occur. They are well suited to this purpose as they are able to speed up chemical reactions without being used up themselves. The diagram below ilustrates the amount of energy activation needed in a reaction without an enzyme in comparison to with an active enzyme reaction.

With the required activation energy lowered, the reaction reaches the same result but in less time, as the reaction can occur faster.

Several factors affect how an enzyme works within a reaction. Such as:

Temperature:
As we know, temperature has an effect on most chemical reactions. This effect is different and always apparent in enzyme reactions. In typical reactions, the increase of temperature in a reaction also speeds up the rate of reaction. With enzyme reactions, this is true to a certain extent. Once a certain temperature is reached, bonds begin to break in the enzyme. These are bonds that hold the 3D shape of the enzyme together, when these bonds break the shape of the active site changes and no longer fit the substrate. The enzyme has then become “denatured”. The denaturing of an enzyme is irreversible.

(GRAPH GOES UP STEADILY, THEN SUDDENLY BACK DOWN)

pH:
With pH, there are similar affects to the change of temperature on the reaction. Enzymes tend to have particular optimum pH’s that they work best at. Being away from this optimum pH, whether the pH is higher or lower, affects the rate of reaction. This is because the different pH’s can change the shape of the enzyme’s active site, which in turn will alter how well it will fit to its substrate. At extreme pH’s the hydrogen bonds may break and denature the enzyme.

(GRAPH GOES UP AND BACK DOWN AT SAME RATE)

Substrate concentration:
The concentration of the substrate in the reaction will affect the rate of the reaction up to a certain extent. The more substrate that is floating around in the reaction will allow for more bonds of substrate to enzyme. But after a certain amount, it will get to a point where each enzyme’s active site is saturated and the excess substrate will not change the rate of reaction any further.

(GRAPH GOES UP THEN LEVELS OUT)

M3 - Use data from experimental work to explain the role of enzymes in the body.

To illustrate how two factors (substrate concentration and temperature) affect the rate of reaction in an enzyme reaction, two similar experiments were conducted.
The basic idea of the experiment was to react samples of Potato with Hydrogen Peroxide and measuring the amount of gas released. The enzyme in the reaction is known as Catalase. To prepare the experiment, the following steps were