Macromolecules
I. Introduction
A. Define categories of macromolecules
1. Carbohydrates
a. monomer- sugar
b. linkage- glycosidic
2. Protein
a. Monomer- amino acid
b. Linkage- peptide bond
3. Lipid
a. Monomer- Fatty acid, glycerol
b. Linkage- ester
4. Nucleic acids
a. Monomer- nucleotide
b. Linkage- Phosphodiester
B. Refer to bullet handout for details of introduction
II Procedures
A. Tests for Carbohydrates
1. Iodine test for the presence of starch.
http://www.elmhurst.edu/~chm/vchembook/548starchiodine.html
a. Iodine intercalates into the helical structure of starch polymers
resulting in the color change from yellow to blue/black
b. add 3- 5 drops of IKI reagent to approximately 1 ml of sample
to be tested.
i. If sample is a solid, a slurry of the solid can be made with
water to facilitate testing.
c. a positive result is a blue/black color
d. a negative result is a yellow/brown color. (anything other than
blue/black/grey is considered negative)
2. Benedicts test for reducing sugar
http://www.biosci.ohiou.edu/introbioslab/Bios170/170_2/benedict.htm
a. The Cu+2 ion contained within the reagent is reduced to Cu+ by
reacting with the free aldehyde or ketone group present in all
monosaccharides and some disaccharides.
b. Mix approlomately equal volumes of solution to be tested with
the Benedicts reagent. Heat in boiling water bath for 5 minutes.
c. positive test is noted for color changes to green, orange, brick
red or brown.
d. Negative results are seen as blue (No color change)
B. Tests for lipids
1. Brown paper test
a. Lipids do not evaporate readily into air. They do, however,
impregnate uncoated brown paper to form a translucent spot.
Unlike aqueous solutions, the lipid residue will not disappear
(evaporate) after 30 minutes.
b. Spot one drop of substance to be tested onto a piece of brown
paper. Observe after 30 minutes for translucency.
2. Emulsion test
a. Lipids do not dissolve in water, but do dissolve in ethanol. This
characteristic is used in the emulsion test.
b. Do not start by dissolving the sample in water, but instead
shake some of the test sample with about 4 ml of ethanol. Decant
the ethanol/ lipid solution into a test tube containing 4-8 ml of
water. (leave any undissolved substances behind.) If there are
lipids dissolved in the ethanol, they will precipitate in the water,
forming a cloudy white emulsion.
C. Tests for Protein
1. Biuret test.
http://www.biosci.ohiou.edu/introbioslab/Bios170/170_2/biuret.htm
a. Biuret reagent contains Cu+2 ions that form of a tetracoordinated cupric ion (Cu+2 ) with amino groups participating in a
peptide bond. This complex is violet in color. Note- a minimum of
3 amino acids must be covalently bonded via peptide bonds to
react positively with biuret reagent.
b. Add equal volumes of substance to be tested and biuret reagent
to a test tube. Mix and observe for color change.
c. positive results appear violet or rose colored. (Roe color
indicates presence of short chain polypeptides.)
d. Negative results appear to remain blue in color.
e. Production of a yellow color indicates the presence of a strong
acid that interferes with the accuracy of this test.
D. Design an experiment to test for the presence of each of the above 3 categories
of macromolecules in various food substances of choice.
Hints:
 Substances to be tested should be ground into a slurry with water until
they are liquid enough to be pipetted.
 Incorporate a positive control and a negative control for each test
performed.
E. Based on what you know about living organisms, would you expect many food
substances to contain nucleic acids?