Observation:
Discussion:
Firstly iodine forms a complex with the starch solution to give the characteristic blue-black color. Starch consists of two types of molecules, amylose (normally 20-30%) and amylopectin (normally 70-80%). The unbranched amylose is a chain of glucose molecules bounded together. The chain is coiled in the shape of a helix.
Fig 1 Starch-iodine complex
The iodine inserts itself into the helix making it rigid. This changes the color to blue. When heat is applied, the complex is destroyed and the solution becomes colorless.
This occurred in test tube 3 to which heat was added. The other test tubes did not become decolorized because no heat was applied.
Once the enzyme amylase was added to the starch-iodine solution a purple coloration was observed which indicated the presence of a protein that the enzyme would be able to act upon. In test tube 3 the reaction moved the fastest because heat was applied to the reaction. The reason for this is because increase in the rate at which the enzyme and the starch substrate collide, the amylase has an optimum shape or flexibility and will hold this ideal shape at the optimum temperature. For pancreatic amylase this will be at body temperature. Because this enzyme does well at high temperatures, its structure will remain more rigid and inflexible held together by disulfide bridges between different regions of the enzyme structure. It was also observed that that test tube 2 gradually decolorized as the temperature of the water bath increased from 20oC. This showed that as the temperature increased the rate of the reaction at which the amylase broke down the amylase in the starch also increased. Test tube1 was the last to become decolorized because it had the lowest temperature of10oC. When the solution reached the temperature where the enzyme could best break down the amylose the solution started to decolorize showing movement in the rate of the reaction.
Experiment 2
Title: Preparation of enzyme catalase
Aim: To observe enzyme reaction of a catalase.
Date: 29 September 2004
Theory:
Catalyse is an enzyme found in food such as potato and liver. It is used for removing hydrogen peroxide from the cells. Catalyse speeds up the decomposition of hydrogen peroxide into water and oxygen. It is able to speed up the decomposition of hydrogen peroxide because of the shape of the hydrogen peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction. Hydrogen peroxide will breakdown to oxygen and water in the presence of catalase. The reaction will increase with increasing enzyme concentration when molecules of hydrogen peroxide are freely available. However, when molecules of the substrate are in short supply, the increase in rate of reaction is limited and will have little effect.
Materials:
1. potato 2. distilled water 3. filter paper
4. mortar & pistil 3. biuret reagent 6. 3% H2O2
7. measuring cylinder
Procedure:
- 1 raw potato was cut in to fine pieces and mashed in a mortar.
- To the potato 100 ml of distilled water was added.
- It was made to stand for 10 minutes and after the extract was gathered through a filter paper.
- 5ml of the extract was placed in a test tube and a biuret test was done on it.
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To another 5ml of the extract 1 ml of 3% H2O2 was added and observed.
- Observation recorded.
Observation:
1. Potato extract + biuret solution light blue color with diluted potato extract; dark blue color with potato extract.
2. Potato extract + 1ml 2H2O2 2H2O + O2 ( O2 released; shown by a fizzy white foam; potato extract has a peach coloration.
Discussion:
The test of the biuret with the potato extract gave a light blue coloration when the potato extract solution was diluted and a dark blue coloration when the extract was left in its concentrated form. This indicated a presence of amylose in the potato.
When the hydrogen peroxide was added to the solution, it evolved oxygen. However, the concentration level of the catalase determined the amount of oxygen that would be evolved. Using a concentrated solution there was a great amount of oxygen evolved by the amount of fizzing occurring in the test tube. When the extract was diluted with water and hydrogen peroxide added again the amount of fizzing was less, which indicated that there was less oxygen evolved because there were fewer enzymes with active sites for the substrate to bind to.
Conclusion:
In an enzyme reaction, many things affect the rate of the reaction. It can be temperature as in the case of the amylase where the rate of the reaction increased as the temperature increased until it reached an optimal temperature where the rate would not increase any further even if the temperature was increased more. Then enzyme concentration can also affect the rate of the reaction by increasing or decreasing the amount of active sites for the substrate to bind and finally, the substrate concentration can also affect the rate of the reaction because if substrate concentration is less than the enzyme concentration the reaction will reach a peak where all the substrates have bonded and then taper off and reduce since there are no more substrates for the active sites or if there are too much substrate and not enough active sites for them to bind.