BIOLOGY 12 - IDENTIFICATION OF BIOLOGICAL MOLECULES
INTRODUCTION
There are a number of simple tests that are commonly used to determine the presence of the biologically important
molecules we have been studying in class. In this lab, you will use sever standard laboratory procedures biologists use to
determine the presence of proteins, carbohydrates (monosaccharides and polysaccharides), and lipids. Often, several of
these tests must be combined, and used with other laboratory techniques (such as gas chromatography and NMR (nuclear
magnetic resonance) to determine the composition of an unknown sample. The lab will consist of four parts:
Part 1: Identification of Proteins Part 2: Identification of Carbohydrates Part 3: Identification of Lipids
Part 4: Identification of Unknowns
PURPOSE
To detect for the presence of proteins, lipids, and carbohydrates in different biological samples.
APPARATUS AND MATERIALS
For All Parts
4 test tubes
test tube rack
10 ml graduated cylinder
For Part 1: ID of Proteins
Albumin solution (from egg whites, premixed)
soft tofu
Biuret reagent (**WARNING - BIURET'S REAGENT IS
EXTREMELY CORROSIVE)
For Part 2: ID of Carbohydrates
Dextrose (dextrose is another name for the
monosaccharide glucose)
starch solution (i.e. corn starch & water)
apple
For Part 3: ID of Lipids
vegetable oil
potato chips
For Part 4: ID of Unknowns
3 unknown solutions
Biuret, Iodine
unglazed paper
-
safety goggles
dropping pipettes
tap water
-
(recipe for Biuret's reagent: 2 Ml NaOH, 4 drops 0.02 M
CuSO4)
2% Milk
-
candy (____________________________________)
IKI (iodine solution)
Benedict's Solution (detects monosaccharides)
-
2% Milk (** 2% milk is actually 31% fat!)
unglazed paper (i.e. paper towel)
OBSERVATIONS AND RESULTS
-
for each Part, set up data tables like the following:
Table __ : (type of test)
Sample
Name
1
2
3
4
Observation
PROCEDURE
PART 1 - ID of Protein
1.
Label the test tubes with the names of the samples. Use
a grease pencil or a pencil.
2.
1. 2 to 3 ml of albumin
2. a small piece soft tofu
3. 2-3 ml milk
4. ~ 3 ml of water to the control tube (control)
3.
Add 2 ml of Biuret reagent to each test tube and gently
shake each tube.
4.
5.
Biuret reagent detects protein by combining with peptide
bonds. If there are peptide bonds present (and therefore
protein), the solution will turn a pinky violet solution.
Record your observations in your table, and state
whether protein is present.
To compare what a "negative" reactive looks like, also
test a tube contain only tap water. This is your control.
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BIOLOGY 12 - IDENTIFICATION OF BIOLOGICAL MOLECULES
PART 2 - ID of Carbohydrate
You will need 2 tables (test for monosaccharides and test for polysachararides) each with spaces for observations of 4 samples.
1.
We will first test for monosaccharides. Label test tubes
1-4.
Add the following to the separate test tubes:
1. 2 to 3 ml of dextrose
2. a small piece of apple <.5cm 3 with 2ml of water
3. candy pieces to the first tube with 2ml water
4. ~ 3 ml of water to the control tube (control)
Add 5 drops of Benedict's solution to the tubes.
Have one group member place the test tubes in a hot
water bath (there will be one set up for you for all
2.
3.
4.
students to use). Leave in for 2 to three minutes and
observe any colour changes. Other group members
should work on the IKI test.
5.
**
6.
7.
7.
8.
If a coloured precipitate forms, then there has been a
positive reaction for monosaccharides.
NOTE: Do not touch the water bath with your hands.
Use TONGS to carefully remove your test tube from
the bath, and let it cool before touching it!
IKI test for starch. Label 4 test tubes 1-4.
Add the following to the separate test tubes:
1. 2 ml of starch solution
2. a small piece of apple <.5cm 3 with 2ml of water
3. candy pieces to the first tube with 2ml water
4. ~ 3 ml of water to the control tube (control)
Add 3 or 4 drops of IKI solution to each tube, and
observe any changes.
A positive reaction will occurs if a colour change of blueblack occurs.
Part 3: ID of Lipids
1.
First do a "Grease Spot/Translucence). Place a small
2.
After 5 minutes, hold the paper up to the light and look for
amount of the sample to be tested on apiece of unglazed
any translucent spots.
paper. Label each sample right on the paper and spread
3.
If a translucent spot is visible, then the presence of lipid
it as thinly as possible (use a stirring rod or plastic knife
has been verified. Record your observations.
to do this). Use tap water as a control.
Part IV: ID of Unknown
You will need 4 separate tables, one for each of the tests that you are going to conduct. (Proteins, monosacharides, polysaccarides and
lipids)
1.
You will obtain samples of 3 unknowns. Label your test
your test tube and get more of the unknown for each test.
tubes 1, 2, 3, and add about 2 ml of each solution for
Your kind and good-looking teacher may or may not ask
each test.
that you skip one or more of the tests.
2.
Using the techniques learned in parts 1-3, test for the
3.
Clean everything up as conscientiously as if the eternal
presence of lipids (do only the paper-towel test for lipids).
future of your immortal soul depended on it. Amen.
carbohydrates, and protein. You will need to clean out
***
TO CLEAN UP, RETURN EVERYTHING TO ITS ORIGINAL PLACE, CLEAN AND DRY ALL GLASSWARE, CLEAN ALL PIPETTES, STIR
RODS, GRADUATED CYLINDER ETC., AND MAKE SURE YOUR WORK AREA IS CLEAN AND DRY.
QUESTIONS
1.
2.
3.
4.
5.
6.
7.
What happens to proteins when they are exposed to very
high temperatures?
Contrast carbohydrates and proteins in relation to their
chemical structure and their functions in the organism.
Name some foodstuffs high in carbohydrate content.
Although carbohydrates are a rich source of energy, can
people survive on a diet consisting only of
carbohydrates? Explain.
What biological process provides all of the carbohydrates
consumed by man?
In what form is excess carbohydrate stored in an animal?
In a plant?
Did your sample test positive fro more than one test?
Explain why this might occur.
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