An investigation to look at the effect of temperature on enzyme activity

Biology Coursework

Introduction

The success of living organisms is due to the cell’s ability to make protein catalysts, or enzymes, each with precisely specified properties. Each enzyme has a unique shape containing an active site. This active site binds a particular set of other molecules (called substrates) in such a way as to speed up a particular one of the many chemical reactions that the substrates can undergo (by a factor of up to 1014). Like all other catalysts, enzyme molecules themselves are not changed after participating in a reaction and therefore can function over and over again.

Enzymes are usually irreversibly damaged (or denatured) under certain conditions such as high temperatures above about 45oC. The pH affects the activity of enzymes, in a similar way to temperature. A pH that’s much higher or lower than the optimum pH causes the enzyme to denature. When a protein is denatured by heat or change in pH, the folding of the enzyme and its active site is messed up and it does not work.

Large food molecules must be broken down into smaller molecules before our cells can use them. The stomach produces protease enzymes, which break down large protein molecules into smaller ones. The stomach also produces hydrochloric acid (HCl) to give the right pH for the protease enzymes to work (pH2 – acidic). Protease enzymes in the small intestine then break down the smaller proteins into amino acids.

In our experiment we will use will be pepsin, one of the protease enzymes found in the stomach. We will use it to break down another protein, albumen (egg white). The albumen is cloudy, but when we add the pepsin at the right pH and temperature it will turn clear, meaning that the pepsin enzyme has broken down the albumen into smaller protein molecules. We will place a bit of paper with a cross drawn on it under the bottom of the test tube, and time how long it takes for the cross to become clearly visible.