Name: _____________________________________________________ Hour: ______ Biology 2012-2013
Biology Unit 1-Biomolecule Identification Lab
Objectives:
- Apply knowledge of biomolecule reagents to identify types of biomolecules.
- Identify the type of biomolecule present per unknown sample.
- Identify the chemical function of each biomolecule per unknown sample.
Background:
Reagents are chemicals that we will be using in this lab to identify different types of
biomolecules. Recall that there are 4 types of biomolecules: carbohydrates, lipids, proteins and
nucleic acids. In this lab we will be conducting two different tests for carbohydrates, a test for
lipids and a test for proteins. You will be provided 5 unknown samples, each containing one
type of biomolecule. You will be reacting the chemicals with each unknown sample to thereby
identify the biomolecule present, and the given cellular function of each sample.
To test carbohydrates we will be using Benedict’s Solution and Iodine. Benedict’s
solution is used to test for the presence of monosaccharides. Benedict’s solution is naturally a
light, clear blue colored solution. If the Benedict’s Solution turns the sample an opaque
yellow/orange color, this shows the positive presence of monosaccharides. Iodine is used to test
for the presence of polysaccharides. Iodine is naturally a dark amber (or yellow-brown) color.
However, if the iodine turns the sample a very dark black-purple color, this shows the positive
presence of polysaccharides.
When testing for lipids, we will combine samples with Sudan IV powder. Sudan IV
powder only binds with lipid molecules. If Sudan IV powder is mixed with a solution not
containing lipids, it will simply separate out and float on the surface like dust or debri. If the
powder is mixed with a solution containing lipids, you can expect to see it stain the entire
solution a deep red color.
Lastly we will test for the presence of proteins using Biuret Solution. Biuret in its natural
state is a light pink/red color. However, when mixed with a solution containing protein, it will
change the color to a light violet or lilac color.
Your job is to conduct an experiment per unknown sample, in order to identify the
present biomolecule. You and your group will then collect your observed data, and report out
to the class with your findings.
Hypotheses:
All hypotheses should be in the “If _______, then______.”-format. A hypothesis is not a
random guess you pull out of thin air, but should be a logical and educated prediction, using
known scientific concepts.
For the following write out a hypothesis for each reagent test:
(1) For the Benedict’s Test:
If ____________________________________________________________________ ,
then __________________________________________________________________ .
(2) For the Iodine Test:
If ____________________________________________________________________ ,
then __________________________________________________________________ .
(3) For the Sudan IV Test:
If ___________________________________________________________________ ,
then __________________________________________________________________ .
(4) For the Biuret Test:
If ____________________________________________________________________ ,
then __________________________________________________________________ .
Reagent Results (Quick Review)
Reagent
Benedict’s
Iodine
Sudan IV
Biuret
Positive Test
Negative Test
Experiment Directions:
-
You will be working in groups of 3.
Each group will be assigned only one type of reagent test.
Once your assigned test is completed, record your data and sit down.
The class as a whole then will compile their collected data.
Benedict’s Test Directions:
1- Place ½ pipette of each unknown sample into
its own individual test tube. (Make sure the
labels correspond correctly. *Use test tube
rack.)
2- Mix ½ a pipette of Benedict’s Solution into
each unknown sample test tube. (*Use test
tube rack.)
3- Carefully place each test tube into the hot
water bath.
4- Allow test tubes to sit in the water for 510minutes (until a color change is observed).
5- Carefully take the test tubes out of the hot
water bath using test tube tongs, and place
back in test tube rack.
6- Record observations in “Benedict’s Test Data
Collection”.
7- Sit and begin working on your section’s
analysis and conclusion until the class is ready
to progress.
Sudan IV Test Directions:
1- Place ½ pipette of each unknown sample into
its own individual test tube. (Make sure the
labels correspond correctly. *Use test tube
rack.)
2- Use the toothpick to drop a small amount of
Sudan IV powder into each unknown sample
test tube. (*Use test tube rack.)
3- Carefully mix each solution by flicking the
base of the test tube.
4- Record observations in “Sudan IV Test Data
Collection”.
5- Sit and begin working on your section’s
analysis and conclusion until the class is ready
to progress.
Iodine Test Directions:
1- Place ½ pipette of each unknown sample into
its own individual test tube. (Make sure the
labels correspond correctly. *Use test tube
rack.)
2- Mix ½ a pipette of Iodine Solution into each
unknown sample test tube. (*Use test tube
rack.)
3- Carefully mix each solution by flicking the
base of the test tube.
4- Record observations in “Iodine Test Data
Collection”.
5- Sit and begin working on your section’s
analysis and conclusion until the class is ready
to progress.
Biuret Test Directions:
1- Place ½ pipette of each unknown sample into
its own individual test tube. (Make sure labels
correspond correctly. *Use test tube rack.)
2- Mix 5-10 drops of Biuret Solution into each
unknown sample test tube. (However many
drops you choose, make sure it is consistent
between test tubes.)
3- Carefully mix each solution by flicking t base
of the test tube.
4- Record observations in “Biuret Test Data
Collection”.
5- Sit and begin working on your section’s
analysis and conclusion until the class is ready
to progress.
Data Collection
Benedict’s Test
Unknown
Sample
Water (Control)
Observations
Positive / Negative Test
1
2
3
4
5
Iodine Test
Unknown
Sample
Water (Control)
1
2
3
4
5
Observations
Positive / Negative Test
Sudan IV Test
Unknown
Sample
Water (Control)
1
2
3
4
5
Observations
Unknown
Sample
Water (Control)
1
2
3
4
5
Observations
Positive / Negative Test
Biuret Test
Positive / Negative Test
Analysis & Conclusion
(1) What was the purpose of running the reagent tests on the distilled water?
__________________________________________________________________________
(2) For each solution identify which biomolecule was present, and how you know this:
Biomolecule Present
How Do You Know This?
Unknown Sample
#1
Unknown Sample
#2
Unknown Sample
#3
Unknown Sample
#4
Unknown Sample
#5
(3) Connect the Unknown Samples to their Monomers and Polymers:
Question
Which sample could contain
glucose or fructose?
Which same could contain
fatty acids?
Which sample could contain
nucleotides?
Which sample could contain
disaccharides?
Which sample could contain
polysaccharides?
Which sample could contain
polypeptides?
Which sample could contain
glycerol?
Which sample could contain
amino acids?
Which sample could contain
monosaccharides?
Unknown
Sample #
How do You Know This?
(4) Connect the Unknown Samples to their Biomolecule Functions:
Question
Unknown
Sample #
How do You Know This?
Which sample could provide
your cells with immediate
energy?
Which sample could your
cells use to store long term
energy?
Which sample would probably
provide your cells more with
intermediate energy (rather
than immediate)?
Which sample might be able
to catalyze chemical reactions
inside your cells?
Which sample could possibly
form the cell membranes?
Which sample is the
expression of DNA/RNA?
(5) You are given another scientist’s biomolecule data. Analyze their data table and
draw conclusions.
Reaction
with Biuret
Water
Sample-X
Sample-Y
Sample-Z
Sample-A
Sample-B
-+
-----
Reaction
with
Benedict’s
-----+
Reaction
with Sudan
IV
--+
----
Reaction
with Iodine
---+
---
A- Looking at the data for Sample-X, provide all of the details you can conclude about
the solution:
Monomer/s:
Polymer/s:
Possible
Cellular
Functions:
B- Looking at the data for Sample-Y, provide all of the details you can conclude about
the solution:
Monomer/s:
Polymer/s:
Possible
Cellular
Functions:
C- Looking at the data for Sample-Z, provide all of the details you can conclude about
the solution:
Monomer/s:
Polymer/s:
Possible
Cellular
Functions:
D- Looking at the data for Sample-A, provide all of the details you can conclude about
the solution:
Monomer/s:
Polymer/s:
Possible
Cellular
Functions:
E- Looking at the data for Sample-B, provide all of the details you can conclude about
the solution:
Monomer/s:
Polymer/s:
Possible
Cellular
Functions: