BIOL 130 Lab Report
Identifying Two Macromolecules Carbohydrates and Proteins
[Type the company name] INTRODUCTION
As the name suggests, macromolecules are large molecules that make up more than 90%
of the total cell mass. These biological macromolecules vary greatly in size - from several
hundred to several hundred million molecular weight units - and are made up of monomer units.
There are four major classes of biological macromolecules: proteins, carbohydrates, lipids, and
nucleic acids (Sheeler & Bianchi, 1980). Proteins are made up of polymers of amino acids. The
shape and structure of a cell is defined by proteins (Alberts et al., 1989). Carbohydrates are
made up of polymers of simple sugars called monosaccharides. Carbohydrates can also be made
up of two sugars, three sugars or more, and they are called disaccharides and polysaccharides
respectively (Sheeler & Bianchi, 1980). Lipids are a collection of molecules that are insoluble in
water but soluble in non polar solvents. Common lipids include fatty acids, glycolipds, neutral
fats, and so on (Sheeler & Bianchi, 1980). Nucleic acids store and transfer all kinds of genetic
information and are polymers of nucleotides (Pollard & Earnshaw, 2004).
The experiment performed was designed to identify the biological macromolecules.
These biological macromolecules are to be identified by the changes in colour through three
different tests - Iodine Test for starch and glycogen, Benedict's Test for reducing sugars, and
Biuret Test for Proteins. However, only two macromolecules are being identified in this
experiment - carbohydrates and proteins. There are 12 solutions to be tested in this experiment.
The Iodine test is used to indentify starch and glycogen in the given solutions. Of the 12
solutions, solution 8 is a starch solution and solution 7 is a glycogen solution. Starch solutions
turn blue-black when Iodine solution is added to it. This is due to the formation of polyiodide
chains when the Iodine solution mixes with starch. Starch contains both amylose and
amylopectin. The amylose molecules in starch form helices at the locations where the Iodine
2 molecules assemble. This cause a dark blue-black colour change ("Starch-iodine test", 2008).
Therefore, solution 8 should turn blue-black when Iodine solution is added to it since it is a
starch solution. However, glycogen solutions turn red-brown when Iodine solution is added. The
chemical structure of glycogen is similar to the structure of amylopectin. Glycogen is highly
branched. These branches are formed through acetal linkages. It is because of the highly
branched structure of glycogen that solutions of glycogen turn red-brown in Iodine solutions
(Ophardt, 2003). Thus, solution 7, a glycogen solution, should turn red-brown with the addition
of Iodine solution. Solution 12 is an unknown, unknown 318.
The Benedict's Test is used to identify reducing sugars. Reducing sugars are sugars that
contain free aldehyde or ketone groups that are oxidized into carboxylic acids. The Benedict's
solution contains blue Cu ions. These ions react with the electrons from aldehyde or ketone
group, reducing the Cu ions to Cu ions to form a red-brown precipitate of Copper (I) Oxide
(Hunt, n.d.). A change in colour to red-brown indicates the presence of sugars. Of the 12
solutions, solution 4 is a solution of honey. This solution should turn red-brown since honey
contains sugars. Solutions 1(glucose solution), 3(maltose solution), 5(sucrose solution), and
6(lactose solution) should turn red-brown as well. This is because glucose, maltose, sucrose, and
lactose are sugars. There should be no change in colour in the other solutions. However, since
solution 12 is an unknown solution, we do not know if a colour change will take place.
The Biuret Test is used to identify the presence of proteins in a solution. During the
Biuret Test, 2 mL of 10% NaOH and 5 drops of 1% CuSO solutions are added to every test tube.
Proteins are made up of polypeptides of amino acid chains linked together by peptide bonds.
The polypeptide backbone includes Nitrogen from the amino group of the amino acid, the α-
carbon, and the carbonyl carbon from the carboxyl group (Pollard & Earnshaw, 2004). The
3 CuSO solution contains Cu ions that cause protein solutions to turn violet when they stick to
the Nitrogen atoms of the amino group (McRae, n.d.). Of the 12 solutions, solution 9 should turn
violet because it was originally a protein solution. However, none of the other solutions should
turn violet, and the colour change of the unknown 318 solution cannot be predicted yet.
Please refer to Biology 130 Lab Manual, Department of Biology 2013, pages 13-14. No other
deviations were made from this procedure.
Please refer to Biology 130 Lab Manual, Department of Biology 2013, pages 14-18. No other
deviations were made from this procedure.
Table 1: Observations of the Iodine Test for Starch and Glycogen
Test Tube Colour before Colour after Positive/Negative
#1 (1% glucose Clear transparent No change(clear Negative
#2 (0.3% glucose-1- Clear transparent No change(clear Negative
#3 (1% maltose Clear transparent No change(clear Negative
#4 (honey solution) Slightly translucent No change(clear Negative
#5 (1% sucrose Clear transparent No change(clear Negative
#6 (1% lactose Clear transparent No change(clear Negative
#7 (1% glycogen Translucent Red-brown Positive
#8 (1% starch Slightly translucent Blue-black Positive
#9 (protein solution) Translucent No change(clear Negative
#10 (beer) Brown- yellow No change(clear Negative
#11 (distilled water) Clear transparent No change(clear Negative
#12 (unknown Slightly translucent Red-brown Positive
5 * Unknown 318 (7.5mL)
Table 2: Observations of the Benedict's Test for Reducing Sugars
Test Tube Colour before Colour after Colour change Positive/Negative
#1 (1% glucose Clear transparent Light Blue Light red-brown Positive
#2 (0.3% Clear transparent Light blue No change (light Negative
#3 (1% maltose Clear transparent Light blue Red-brown Positive
#4 (honey Slightly Light blue Brown Positive
#5 (1% sucrose Clear transparent Light blue No change (light Negative
#6 (1% lactose Clear transparent Light blue Red Positive
#7 (1% glycogen Translucent Light blue No change (light Negative
#8 (1% starch Slightly Light blue No change (light Negative
solution) translucent blue)
#9 (protein Translucent Light blue No change(light Negative
#10 (beer) Brown- yellow Green-blue Pale thick yellow Positive* 1
6 #11(distilled Clear transparent Light blue No change Negative
#12 (Unknown Slightly Light blue Red-orange Positive
solution 318)* translucent
*1Positive because although it did not turn red/brown, there was a colour change and a coloured
* Unknown 318 (7.5mL)
Table 3: Observations for the Biuret Test for Protein
Test Tube Colour Before ColourAfter Positive/Negative
#1 (1% glucose Clear transparent Slightly blue(due to Negative
solution) CuSo 4
#2 (0.3% glucose-1- Clear transparent Slightly blue(due to Negative
phosphate) CuSo 4
#3 (1% maltose Clear trans