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Testing for Macromolecules

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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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