Testing for Macromolecules
Essay by Surina Dulat • October 15, 2016 • Lab Report • 1,545 Words (7 Pages) • 2,042 Views
Testing for Macromolecules
Surina Dulat 20669629
Partner: Umeira Vijendr 20672777
T.A: Jeannette Lam, Vivian Tan
Section 015
BIOL 130L
Lab Section date: October 5, 2016 2:30pm
Date of experiment: September 28, 2016
Introduction
The objective of this lab is to determine the macromolecule(s) present in each solution and use that information to identify the macromolecules(s) present in the unknown solution. Many living organisms are composed of atoms that are linked together to make larger molecules known as macromolecules. The different types of macromolecules are carbohydrates, proteins, lipids, and nucleic acids. Starch and glycogen are carbohydrates. Therefore, to test for them in solutions, the Iodine test is performed. The test consists of adding 1 drop of iodine solution to each sample and waiting for the solutions to change to either a blue-black colour to indicate starch is present or a reddish-brown colour to indicate that glycogen is present (Bates, French, Rundle, 1943, p. 142). Similarly, when testing for proteins, the Biuret test is used. To test for protein in the solutions, 2mL of 10% sodium hydroxide solution and 5 drops of 1% copper sulfate is added to each solution and the colour change is observed (Bhandary, Kumari N., Bhat, K.P, Bekal, 2012, p. 36). If the solution changes to a violet colour, it indicates protein is present (Bhandary et al, 2012, p. 36). In the Benedict’s test, 2mL of Benedict’s solution is added to each solution and the contents are boiled for 5 minutes each then observed for colour change ranging from yellow to green or red to brown for a positive result (Bhandary et al, 2012, p. 36). There are positive and negative results that occur in each test. A positive test result means that the experiment has worked according to your hypothesis while a negative test result means that the experiment’s substance that is being tested has not changed (Andreoni, 1995).
Materials and Methods
Please refer to pages 20-24 of the fall 2016 BIOL 130l manual for material and methods for this la. All steps founded without any deviations (Department of Biology, 2016).
Observation and Results
Table 1: Iodine Test for starch and glycogen
Test tube number | Before colour change | Positive/negative reaction | After colour change |
1 | 15ml of 1% glucose solution (clear) | Negative | Yellow |
2 | 15ml of 0.3% glucose-1-phosphate (clear) | Negative | Yellow |
3 | 15ml of 1% maltose solution (clear) | Negative | Yellow |
4 | 15ml of honey solution (yellow) | Negative | Yellow |
5 | 15ml of 1% sucrose solution (clear) | Negative | Yellow |
6 | 15ml of 1% lactose solution (clear) | Negative | Yellow |
7 | 15ml of 1% glycogen solution (clear) | Positive | Reddish-brown (glycogen present) |
8 | 15ml of 1% starch solution (clear) | Positive | Blue-black (starch present) |
9 | 15ml of protein (clear) | Negative | Yellow |
10 | 15ml of beer (clear) | Negative | Yellow |
11 | 15ml of distilled water (clear) | Negative | Yellow |
12 | 15ml of unknown #72 solution (clear) | Positive | Blue-black (starch present) |
The table is the result of the Iodine test which was used to test for starch and glycogen in each solution. Most of the solutions produced negative results except for test tubes #7, 8, and 12. The solutions in test tubes #7, 8 and 12 changed colour therefore they produced positive results. Test tube #8 and #12 turned a blue-black colour to indicate that starch is present while test tube #7 turned reddish-brown to indicate that glycogen is present. In starch, the polymer amylose reacted with the iodine solution which produces the blue colour (Bates et al, 1943, p.143). Since glycogen is very branched compare to starch, therefore, the branched polymer amylopectin reacted with the iodine solution to produce the reddish-brown colour (Bates et al, 1943, p.142).
Table 2: Benedict’s test for reducing sugars
Test tube number | Colour before reaction | Positive/negative reaction | Colour change after 5 minutes of reaction |
1 | 15ml of 1% glucose solution (clear) | Positive | Reddish-brown |
2 | 15ml of 0.3% glucose-1-phosphate (clear) | Negative | Blue |
3 | 15ml of 1% maltose solution (clear) | Positive | Brown |
4 | 15ml of honey solution (yellow) | Positive | Orange-red |
5 | 15ml of 1% sucrose solution (clear) | Negative | Blue |
6 | 15ml of 1% lactose solution (clear) | Negative | Blue (after another 5 minutes, the result was positive and colour was reddish-brown) |
7 | 15ml of 1% glycogen solution (clear) | Negative | Blue |
8 | 15ml of 1% starch solution (clear) | Negative | Blue |
9 | 15ml of protein (clear) | Negative | Blue |
10 | 15ml of beer (clear) | Positive | Green |
11 | 15ml of distilled water (clear) | Negative | Blue |
12 | 15ml of unknown #72 solution (clear) | Negative | Blue (extra 5 minutes, still blue therefore negative result) |
This table shows the results of the Benedict’s test which was used to test for reducing sugars which are sugars that have free aldehyde group (Alberts, Bray, Hopkin, Johnson, Lewis, Raff, Roberts, Walter, 2014, p.53). The reducing sugars in the solution react with the benedict’s solution to produce colours from yellow or green to red or brown. Most test tubes tested negative while some tested positive.
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