An experiment testing on how the temperature affects the rate of reaction between catalase and hydrogen peroxide

Authors Avatar

Nicholas Marshall 11A

An experiment testing on how the temperature affects the rate of reaction between catalase and hydrogen peroxide

Aim:

            My aim is to find out how temperature affects the breakdown of hydrogen peroxide by the enzyme catalyse.

Planning:

Scientific Knowledge-

An Enzyme is any one of many specialised organic substances, composed of polymers of amino acids, that act as catalysts (things that speed up reactions) to regulate the speed of the many chemical reactions involved in the metabolism of living organisms without being used up themselves. 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 including making large molecules from small ones.

Adding ASE to the name of the substrate molecule (the molecule they break up) with which they react usually names the individual enzymes. 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.

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 substrate molecule is in the enzyme it gets tweaked and pulled out of shape, making it split into product molecules. Once the products have been released, the enzyme is ready to bind with a new substrate. The way an enzyme and its substrate fit together can be shown by the lock and key theory:

        Substrate molecule

        Product molecules

                

        Enzyme


Properties of Enzymes 

As the Swedish chemist Jöns 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 zymogene. 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.

So put it simply the following properties apply to all enzymes:

  • All enzymes are proteins- they have molecules with a very precise 3-d shape that also allows an active site (to let in the substrate molecules).
  • All enzymes are catalysts- they speed up the reactions of the body without being used themselves. Therefore a small amount of enzymes can be used over and over again to break down a large quantity of its substrate molecules.
  • All enzymes denature at high temperatures and also have an optimum temperature- enzymes have a temperature where they work best (because of kinetic theory). After that temperature the enzyme starts to denature (this is where the enzymes molecules start to distort and lose shape. As a result the active site isn’t the same shape and so its substrate molecules cant fit and the enzymes efficiency falls dramatically) and so the amount reactions decrease rapidly.
  • All enzymes have an optimum pH- most enzymes work best at neutral (pH 7) because they are proteins, which are damages by very acid or alkaline conditions. There are exceptions of course. For instance any enzymes in the stomach will be able to work at very acidic conditions because of its surroundings.
  • All enzymes are specific to their substrate molecule- this is because their active sites will only allow one kind of substrate molecule in.
Join now!

How does the reaction between the enzyme and substrate molecule occur?

        Basically the enzyme and substrate molecule are moving around in their corresponding area (wherever that might be) and when they hit each other the enzyme locks the substrate molecule in and splits it or does whatever it needs to do (remember the reactions vary). The enzyme then wanders around until it hits another substrate molecule and then splits that. This goes on and on.

The only comment I can make about this is the kinetic theory. This is when heat is applied to molecules and they move ...

This is a preview of the whole essay