Enzyme Investigation

ENZYME INVESTIGATION

Planning

Introduction: An Enzyme is any one of many specialised organic substances, composed of polymers of amino acids, that act as catalysts to regulate the speed of the many chemical reactions involved in the metabolism of living organisms. 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. Many other enzymes catalyse other types of reactions.

Individual enzymes are named by adding ASE to the name of the substrate with which they react. The enzyme that controls urea decomposition is called urease; those that control protein hydrolyses are known as proteinases. Some enzymes, such as the proteinases trypsin and pepsin, retain the names used before this nomenclature was adopted.

( Fig 1.0 on the following page )

Structure and Function of an Enzyme

Enzymes are large proteins that speed up chemical reactions. In their globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate.

Properties of Enzymes

As the Swedish chemist Jцns Jakob Berzelius suggested in 1823, enzymes are typical catalysts: they are capable of increasing the rate of reaction without being consumed in the process.

Some enzymes, such as pepsin and trypsin, which bring about the digestion of meat, control many different reactions, whereas others, such as urease, are extremely specific and may accelerate only one reaction. Still others release energy to make the heart beat and the lungs expand and contract. Many facilitate the conversion of sugar and foods into the various substances the body requires for tissue-building, the replacement of blood cells, and the release of chemical energy to move muscles.

Pepsin, trypsin, and some other enzymes possess, in addition, the peculiar property known as autocatalysis, which permits them to cause their own formation from an inert precursor called zymogen. As a consequence, these enzymes may be reproduced in a test tube.

As a class, enzymes are extraordinarily efficient. Minute quantities of an enzyme can accomplish at low temperatures what would require violent reagents and high temperatures by ordinary chemical means. About 30g of pure crystalline pepsin, for example, would be capable of digesting nearly 2 metric tons of egg white in a few hours.

The kinetics of enzyme reactions differ somewhat from those of simple inorganic reactions. Each enzyme is selectively specific for the substance in which it causes a reaction and is most effective at a temperature peculiar to it. Although an increase in temperature may accelerate a reaction, enzymes are unstable when heated. The catalytic activity of an enzyme is determined primarily by the enzyme's amino-acid sequence and by the tertiary structure-that is, the three-dimensional folded structure of the macromolecule. Many enzymes require the presence of another ion or a molecule called a cofactor, in order to function.

As a rule, enzymes do not attack living cells. As soon as a cell dies, however, enzymes that break down protein rapidly digest it. The resistance of the living cell is due to the enzyme's inability to pass through the membrane of the cell as long as the cell lives. When the cell dies, its membrane becomes permeable, and the enzyme can then enter the cell and destroy the protein within it. Some cells also contain enzyme inhibitors, known as antienzymes, which prevent the action of an enzyme upon a substrate.

Aim: To find the effect of temperature on enzymes, using a potato as a catalyst. The source of catalase is in the potato cells.

Preliminary work: For this, I wanted to see how many potato discs would be a good number to do the actual experiment. I used the same experiment I am going to use to find the effect of temperature on enzymes but instead of varying the temperature, as I am going to do, I varied the amount of potato discs in the test tube. Overall, I took 6 readings of a different number of discs. At first, I used 2; then I went onto 4, and so on up to 12. (2, 4, 6, 8, 10, 12) I found out that the ideal number of discs was 8 so I am going to use 8 in my experiment of varying temperature.

Results of prelim work:

No. of Potatoes

(amount) Time to reach 5cm3

(seconds)

4 41.4

6 33.2

8 30.4

10 20.1

12 18.4

Apparatus: I have decided to use the following equipment in order to carry out my experiment:

? -Water Baths

? -Ice Baths

? -Test Tube/Boiling tube

? -10 cm3 Measuring cylinder

? -2 cm3 of Hydrogen Peroxide

? -1 cm of circular potato chips

? -Manometer

? -Borer

? -Stopwatch

Fig 1.1 is a hand drawn diagram of the equipment I will be using listed above:

Methods: At first, I will have to get the potato so I will use a Borer to cut a cylinder of potato out of the whole one and from there I will cut up the potato cylinder into segments of 1 cm using a razor. I will then put them into a test tube containing 10 cm3 of pH.7 buffer solution and place it in their designated water/ice baths along with the 10 cm3 of Hydrogen Peroxide.