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 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 differs 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.
When hydrogen peroxide is placed on liver (the substrate) it froths
(makes O2)
Possible input variables
These are the things that I could vary in my experiment
Concentration I predict that the reaction will speed up as the
Concentration increases. I think the rate will double because the number
Of hydrogen peroxide atoms in the same volume will double. So there will
be twice as much chemical reacting. Because of this there will be twice
The chance that a hydrogen peroxide molecule will collide with the
Substrate and react. This is why I think the rate will increase.
The reaction will be over quicker but the same amount of oxygen will be
Produced. This is because there is more than enough hydrogen peroxide to react with the liver.
Temperature I think that the reaction will speed up as the temperature
Is increased. The heat will increase the reaction because the heat
Energy will give the hydrogen peroxide molecules energy. Doubling the
Heat will mean the molecules will collide with twice as much energy and
So will be twice as likely to break there bonds.
I also think that there will become a point when the temperature will be
Too hot and too cold for the reaction to work and it will suddenly stop
Producing oxygen. This is because enzymes have optimum working
Temperatures. Because they are organic they can be killed if they get
too hot.
In order to design a suitable experiment and make a credible prediction, I must first explore more closely how temperature is likely to affect the rate of catalysis. Enzymes are specific - they only control one type of reaction; therefore I must use one specific enzyme in my experiment, in order to find a clear way of measuring the rate of reaction. Although they are specific, all enzymes work in a very similar way and have similar properties. They are all globular proteins and are all biological catalysts, they increase the rate of a given reaction without being used up and their presence does not change the nature of the reaction or the end product. Enzymes work by having an active site, made from amino acids. Here, substrate molecules will bind with the enzyme (and other substrate molecules if necessary) and a reaction takes place. The enzyme itself is not affected and releases the new chemical after the reaction. After release of the end product, more substrate molecules can bind with the active site.
Prediction
I predict that the rate of reaction will increase as the temperature increases until the reaction reaches an optimum temperature. Above this optimum temperature, the rate of reaction will fall to zero very quickly, as the enzyme denatures. I must now conduct an experiment to test my prediction. I will do this using the enzymes catalyse. Catalyse is found in most living organisms. It speeds up the catabolic reaction, which breaks down hydrogen peroxide into oxygen and water.
Method
We will measure the amount of Hydrogen peroxide needed for the experiment then put it into the test tube and place into a beaker of water and Heat/cool it to a specific temperature. The Hydrogen peroxide will then be added to the conical flask with the in liver and a bung quickly placed over the top to stop any oxygen escaping. The Oxygen from the reaction will be forced along the tube and in to the measuring cylinder. The oxygen pushes the water out of the cylinder so the amount of oxygen produced can be simply measured by reading off the scale on the measuring cylinder. The stop-clock will be started from the moment when the liver and hydrogen peroxide are mixed. It will be stopped when of oxygen have been produced.
I will do the experiment with the Hydrogen peroxide at
degrees centigrade. I think that this will give me a good range.