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Test for the Presence of Macromolecules

Introduction
In this experiment, we are trying to identify the presence of macromolecules in certain solutions. As in our daily lives, macromolecules are the essential nutrients that we have to take every day, therefore we would like to identify the types of macromolecules that contain in some of the food or solution in order to maintain a healthy life. There are four groups of macromolecules which are carbohydrates, lipids, proteins and nucleic acid. They are mostly made up of hydrogen, carbon, oxygen, nitrogen, sulphur and phosphorus. 1. Carbohydrates

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Carbohydrates are organic compounds that with the combination of carbon, hydrogen and oxygen in a 1:2:1 ratio. Carbohydrates can be separated into three groups, monosaccharide, disaccharides and polysaccharides. Monosaccharide is the monomer of carbohydrates which contain hydroxyl group, such as glucose and fructose. Disaccharides are sugars that contain either aldehydes or ketone that react with hydroxyl group, such as maltose and lactose. Polysaccharides are the long chains of monosaccharide, which is called the polymer of carbohydrates. Monosaccharide and disaccharides can be tested by the Benedict’s test, as they are reducing sugars. Polysaccharides such as starch and glycogen can be tested by the iodine test. Also, carbohydrates are consumed to provide energy to our body and they are useful in metabolism. Therefore, it is one of the essential macromolecule that we have to consume. 2. Lipids

Lipids are made up of a glycerol molecule and three fatty acid molecules. They act as the energy source of human and they made up the phospholipid bilayer of the cell membrane. They can be simply divided into two groups, unsaturated and saturated fat. The only difference between saturated and unsaturated fat in structure is unsaturated fat has a double bond but saturated fat do not. Although some of the lipids can be made by biosynthetic pathway, some of the essential lipids need to be obtained by diets. 3. Proteins

Proteins are made up of a long chain of amino acids called polypeptide, they are formed with the peptide bond. Different proteins are composed with different sequences of amino acids, every protein are made with a specific sequence of amino acid. Proteins are functioned as the transportation between cells, provide support to the cell membrane and produce enzymes that catalyze chemical reactions in bodies. 4. Nucleic acids

Nucleic acids are made up of monomers called nucleotides, each nucleotide consist of a nitrogenous base, a phosphate group and a pentose sugar. They can be divided into two groups, DNA and RNA. The differences between DNA and RNA are DNA has one less oxygen than RNA, also, DNA has the nitrogenous bases of A, T, C and G when RNA has the base U instead of T. They are both important to the forms of life, as they are used in the replication within cell division and pass on the hereditary information. Testes for macromolecules

1. Iodine test
Iodine test is used to test on the presence of starch and glycogen, it is simply performed by adding few drops of iodine solution into the testing solution in the spot plate, then observe for the colour change, if the colour changes from yellow to blue-black, that’s mean the testing solution contains starch. If the colour changes from yellow to brown, that’s mean the testing solution contains glycogen. 2. Benedict’s test

Benedict’s test is used to test on the presence of reducing sugars, all of the monosaccharide and most of the disaccharides. It is simply performed by adding a certain amount of Benedict solution into the testing solution in the test tube, then put into the water bath for around 5 minutes and observe for colour changes. If the colour remain unchanged, which is blue in colour, that’s mean the testing solution does not contain reducing sugar. If the colour did change, ranged from green to brown, depends on how high the glucose level is in the testing solution, or even form precipitate, that’s mean the testing solution contains reducing sugar. 3. Biuret test

Biuret test is used to test on the presence of proteins (peptides), it is simply performed by adding a certain amount of strong base, then add a few drops of copper sulphate and observe for any colour change. If the mixture changes from blue to purple, that’s mean protein is present in the testing solution. If the mixture turns into pink, that’s mean peptides are present but in a short chain.

Material and Methods
Refer to BIOL 130L lab manual, printed for the Fall 2013, section 1 (experiment 1), page 14 to 18, course number: 6388. The unknown solution in the experiment is labeled as number 141.

Results
Number of test tube
Initial colour of the iodine solution
Final colour
Result (+/-)
1
Yellow
Pale yellow

2
Yellow
Really pale yellow

3
Yellow
Pale yellow

4
Yellow
Pale yellow

5
Yellow
Pale yellow

6
Yellow
Pale yellow

7
Yellow
Brown
+
8
Yellow
Blue-black
+
9
Yellow
Yellow

10
Yellow
Yellow

11
Yellow
Pale yellow

12
Yellow
Pale yellow

Table 1: Result of iodine test for starch and glycogen

Number of test tube
Initial colour (with benedict’s solution)
Colour after boiled
Result (+/-)
1
Blue
Reddish-orange
+
2
Blue
Blue

3
Blue
Reddish-orange
+
4
Blue
Brown
+
5
Blue
Blue

6
Blue
Reddish-orange
+
7
Blue
Blue

8
Blue
Light blue

9
Blue
Dark blue

10
Blue
Mustard yellow
+
11
Blue
Blue

12
Blue
Reddish-orange
+
Table 2: Result of Benedict’s test for reducing sugars (carbohydrates)

Number of test tube
Initial colour (with sodium hydroxide)
Final colour (with copper sulfate)
Result (+/-)
1
Clear
Clear blue

2
Clear
Clear blue

3
Clear
Clear blue

4
Clear
Peach
+
5
Clear
Clear blue

6
Clear
Clear blue

7
Clear
Clear blue

8
Clear
Clear blue

9
Clear
Purple
+
10
Brownish-yellow
Green-grey (olive oil)
+
11
Clear
Clear blue

12
Clear
Clear blue

Table 3: Result of biuret test for protein

Discussion
According to Table 1, the colour change shows that test tube 7 contain glycogen and test tube 8 contain starch, as iodine solution will change from yellow to reddish-brown when glycogen is present, and it will change from yellow to blue-black when starch is present. From Table 2, test tubes 1, 3, 4, 6, 10 and 12 change colour, which means all the solution in these test tubes contain reducing sugar, which shows the presence of carbohydrates, in order to have a positive result in the Benedict’s test. From Table 3, the result shows that test tube 4, 9, 10 contain protein as they are the test tubes that changes colour. Test tube 4 which is honey should not contain protein in common, but the result shows that the honey is with a positive result, as the honey we use in this experiment is not the actual honey that collected by the bees, but the manufactured honey that might contain some additives inside that leads to a false positive result.

Reference
BIOL 130L lab manual, printed for the Fall 2013, section 1 (experiment 1), page 14 to 18. Biuret Test for Protein. Retrieved from http://brilliantbiologystudent.weebly.com/biuret-test-for-protein.html Bruce, A., Dennis, B., Karen, H., … Peter, W. (Eds.). (2010). Essential cell biology. Chemical Components of Cells (pp. 39-77). United States of America, USA: Garland Science

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