How do they function?
Enzymes are proteins, and, like all proteins, they consist of amino acids. Their molecules have a very precise three-dimensional shape. This shape includes a “dent” which is exactly the right size and shape for a molecule of the enzyme’s substrate to fit into. This is called the active site. Enzymes perform only one specific job. That means an enzyme can do its job with very few side effects. It also explains why there are so many different types of enzyme. While it is true that an enzyme can only perform one specific job, it is important to know that one enzyme can perform that same job over and over again, millions of times, without being consumed in the process. Not only do enzymes work hard, they also work with blinding speed. For instance, there is an enzyme in the liver called catalase that helps hydrogen peroxide break down into water and oxygen. What's amazing is that one catalase enzyme can break 40 million molecules of hydrogen peroxide each second.
Enzymes in the digestive system
Enzymes play many important roles outside the cell as well. One of the best examples of this is the digestive system. For instance, it is enzymes in your digestive system that break food down into small molecules that can be absorbed by the body. Some enzymes in your digestive system break down starch, some proteins and others break down fats. An enzyme that is able to break fat down would not be able to dissolve protein or starch. The digestive process begins in the mouth. Food is partly broken down by the process of chewing and by the chemical action of salivary enzymes (these enzymes are produced by the salivary glands and break down starches into smaller molecules) like for example amylase. After being chewed and swallowed, the food enters the esophagus on its way to the stomach. After being in the stomach, food enters the small intestine. In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food.
Rate of enzyme activity
Enzyme activity is affected by several factors such as temperature, pH, the concentration of the substrate or of the enzyme, and sometimes even stress. However, the factor which we are testing in this experiment is temperature. Enzyme activity is changed by variation in temperature. As temperature rises the rate of chemical reactions increases because temperature increases the rate of motion of molecules. This leads to more interactions between an enzyme and its substrate. In this experiment the substrate was starch, which is a polysaccharide of glucose. However, if the temperature is too high, enzymes can be denatured and they can no longer bind to a substrate and catalyze reactions. In other words: the enzyme activity will increase as the temperature rises, until a certain high temperature at which the enzyme will denature and be non-functional. Each enzyme has an optimum temperature at which it works best. In this case the enzyme is amylase, which thrives best at temperatures around 40 °C, but above 40 °C the enzyme begins to be damaged, so the reaction slows down. By 60 °C, the enzyme is completely destroyed. 40 °C is therefore the optimum temperature for this enzyme – the temperature at which the rate of the reaction is greatest.
Starch and maltose
Amylase is an enzyme found in the human body, which catalyses the breakdown of starch into maltose through hydrolysis (the reaction with water which causes a compound to separate into its parts – in this case glucose). Glucose is a simple sugar. It is soluble, and quite a reactive substance. It is not, therefore, a very good storage molecule. Being reactive it might get involved in chemical reactions where it was not wanted. It could also dissolve in the water in and around the cell, and might be lost from the cell. Or, when dissolved, it would increase the strength of the solution in the cell, which could damage it. Starch is an energy storage molecule in plants, and it makes up a large part of the food of many organisms. Plants manufacture starch using energy from the sun and then break down the starch to its component sugars, releasing the energy that was stored in the starch molecules. Animals that eat plants can use starch in the same way. Starch is too large to be absorbed into the blood stream directly from the intestine, but many animals have enzymes that break down starch to small sugars. In humans the enzyme amylase, which is present in saliva, accomplishes the breakdown of starch.
Material:
- 4 small beakers.
- A porcelain plate with hollows.
- A test-tube.
- Starch solution.
- Enzyme solution (the enzyme amylase collected from our spit).
- Iodine solution.
Procedure:
- First of all we took 4 small beakers and marked them: Starch solution, Enzyme solution, experiment 1 unheated, and experiment 2 heated.
- Afterwards we diluted the starch solution approximately 3 times with tab water, and mixed it thoroughly.
- Then we collected approximately 2 ml of saliva in the beaker marked enzyme solution from our spit, and diluted and mixed it thoroughly with the same amount of tab water.
- We took approximately half of our 2 ml of enzyme solution and poured it into the test tube, which we afterwards heated in a water bath with boiling water (which means that the water had reached a temperature of 100 °C).
- Then we made a test of starch indicator: Put a drop of starch solution in a hollow in the porcelain plate and then quickly added a drop of iodine solution.
- Afterwards we mixed 1 ml of the enzyme solution with 5 ml of the starch solution, and added a drop of the mixture into a hollow in the porcelain plate. Immediately we added a drop of the iodine solution. We made a sample every 20 second until the samples turned yellow/brown and noted the time.
- Then we repeated everything from the step number 6, but instead of using the unheated enzyme solution we used the heated.
Results:
Discussion:
Looking at the data collected, it appears as though the hypothesis which was developed at the beginning of the experiment was in fact correct. The amylase from our spit did breakdown the starch in the starch solution, and after 80 seconds the colour of the iodine solution went from being dark blue to yellow/brown. And as mentioned in the hypothesis the colour of the iodine solution stayed dark blue after the enzyme solution had been heated.
Conclusion:
In conclusion this experiment further confirmed that enzymes are damaged at a temperature above 60 °C. Each enzyme has its own individual prime functional temperature, therefore if they are removed from these environments they will not function as well or possibly denature if it the temperature is too high. Although, if an enzyme’s optimal temperature is maintained then the enzymes will catalyze reactions at optimum rates.
