In an enzyme-catalyzed reaction, the substance to be acted upon, or substrate, binds to the active site of the enzyme. The enzyme and substrate are held together in an enzyme-substrate complex by hydrophobic bonds, hydrogen bonds, and ionic bonds.
The enzyme then converts the substrate to the reaction products in a process that often requires several chemical steps, and may involve covalent bonds. Finally, the products are released into solution and the enzyme is ready to form another enzyme-substrate complex. As is true of any catalyst, the enzyme is not used up as it carries out the reaction but is recycled again and again. One enzyme molecule can carry out thousands of reaction cycles every minute.
Each enzyme is specific for a certain reaction because its amino acid sequence is unique and causes it to have a unique three-dimensional structure. The "business" end of the enzyme molecule, the active site, also has a specific shape so that only one or few of the thousands of compounds present in the cell can interact with it. If there is a prosthetic group on the enzyme, it will form part of the active site. Any substance that blocks or changes the shape of the active site will interfere with the activity and efficiency of the enzyme. If these changes are large enough, the enzyme can no longer act at all, and is said to be denatured.
What is Hydrogen Peroxide H2O2?
Hydrogen peroxide is a chemical compound, H2O2, a colourless, syrupy liquid that is a strong oxidizing agent and, in water solution, a weak acid. It is miscible with cold water and is soluble in alcohol and ether. Although pure hydrogen peroxide is fairly stable, it decomposes into water and oxygen when heated above about 80°C; it also decomposes in the presence of numerous catalysts. Hydrogen peroxide has many uses. It is available for household use as a 3% (by weight) water solution; it is used as a mild bleaching agent and medicinally as an antiseptic. The 3% solution is sometimes called ten-volume strength, since one volume of it releases ten volumes of oxygen when it decomposes. Hydrogen peroxide is available for commercial use in several concentrations. It is used as a bleaching agent for textiles, e.g., wool and silk, and in paper manufacture. It is also used in chemical manufacture. Hydrogen peroxide (H2O2) is a poisonous byproduct of metabolism that can damage cells if it is not removed. Catalase is an enzyme that speeds up the breakdown of hydrogen peroxide into water (H2O) and oxygen gas (O2).
2H2O2--------catalase--------------> 2H2O + O2
Hydrogen Peroxide is a catalase. A Catalase is nearly ubiquitous among organisms that can grow in the presence of oxygen (air). ..The major function of catalase within cells is to prevent the accumulation of toxic levels of hydrogen peroxide formed as a by-product of metabolic processes - primarily that of the electron transport pathway. ..The only exceptions are the "lactic acid bacteria," which cannot synthesize the fundamental building block porphyrin, and hence do not even possess cytochromes that would otherwise make the toxic H2O2.
.....Each molecule of catalase has four polypeptide chains, each composed of more than 500 amino acids, and nested within this tetrad are four porphyrin heme groups - very much like the familiar haemoglobins, cytochromes, chlorophylls and nitrogen-fixing enzymes in legumes. ..(Catalase may also take part in some of the many oxidatic reactions that occur in all cells.)
Figure 1
Yeast
Yeasts constitute a group of () , a few species of which are commonly used to , , and even drive experimental . A few yeasts, such as , can cause in humans. More than one thousand of yeasts have been described. The most commonly used yeast is , which was domesticated for , , and production thousands of years ago.
Yeasts are single-celled fungi. As fungi, they are related to the other fungi that people are more familiar with.
Rate of Reaction
The rate of the reaction is how quickly the reaction happens. If you imagine the reaction is like a machine, the rate of the reaction is the speed at which the reactants go through the machine. If we know the rate of a particular reaction, then if we want to do it in the laboratory, we can work out how long it's going to take.
Rates of reactions are measured in the amount of product produced in a particular period of time. For instance, it could be measured in per second. It can also be measured in change of concentration per period of time. If you were given the equation
Prediction
I predict that the higher the concentration the quicker the reaction rate will be.
Materials and Method
For materials and method see the front sheet attached.
Health and Safety
- Handle the hydrogen peroxide with care, hydrogen peroxide is highly toxic if come in contact with eyes and mouth.
- Handle all equipments with care
- Wash hands after handling the yeast suspension
- Wash hands after experiment
- Keep hands away from the face when handling equipments and materials.
Raw Results
Analysis of Results
The results obtained show that as time goes by the amount of oxygen produced increases. And as the concentration of the yeast decreases so does the amount of oxygen. The graph clearly shows that when the yeast was less concentrated the amount of oxygen released was much lower than when the ratio of yeast to water was 4:1.
At first there is very little substrate and a lot of enzyme. An increase in the concentration of substrate means that more of the enzyme molecules can be utilized. As more enzymes become involved in reactions, the rate of reaction increases. At some point, all the enzymes are being involved in reactions. When this happens, some of the substrate must "wait" for enzymes to clear their active sites before the enzyme can fit with them (like a "lock and key"). After that, the reaction rate remains flat because increasing amounts of substrate must wait before they can fit with their enzyme.
Evaluation of Materials and Method
The equipment used was quite precise. However the way to get accurate results is to evaluate the method used. The method was quite complex and needed a lot of understanding to unable us to carry out the investigation properly. Time was an important factor in this experiment unfortunately there was lack of it. Therefore the results obtain had some discrepancies and wasn’t very precise. Any number of factors in this lab could have affected the results of this experiment. To get the desired results all of the measurements had to be precisely accurate and fully planned before hand. First of all, the measurements, which were taken, could have possibly been inaccurate. There was also some confusion on the operation of the timer and precise planning in its use.
Also the fact that we had an air bubble at the top of our boiling tube meant that we had lost approximately 1cm3 of oxygen before the experiment even started. If this experiment was to be carried out again a careful analysis of the equipment will be done to make sure that we understand how to read the measurements of the equipment carefully. Also we would have to make sure that we had enough time to do it as well.
Evaluation of Results
There were some uncertainties in the results as the experiment weren’t precise the percentage calculations are done below.
% Uncertainty = accuracy of equipment / measurement taken x 100
% Uncertainty for the cylinder: ±0.1cm3
+ 0.1
5 cm3 0.1 / 5 x 100 = ± 2%
─ 0.1
+ 0.1
4 cm3 0.1 / 4 x 100 = ± 2.5%
─ 0.1
Conclusion
It can be concluded that the higher the concentration the faster the rate of oxygen produced is going to be.
References
Books:
Phillips Concise Encyclopaedia
CXC Biology
Oxford Dictionary
Online references:
MSN Encarta
Software:
Euro press AS/A2 Biology 2005/2006
Letts GSCE Biology 2005
