Exercise 2: Biomolecules
Personal Information
First Name: Richard Anthony
Last Name: Cardenas
Student ID: 201855005
Email: rscardenas@up.edu.ph
Individual Laboratory Output
INTRODUCTION
Organic compounds typically consist of groups of carbon atoms covalently bonded to hydrogen, usually oxygen,
and often other elements as well. They are found throughout the world, in soils and seas, commercial products,
and every cell of the body. The four types most important to structure and function are carbohydrates, lipids,
proteins, and nucleic acids. Carbohydrates are the most abundant macromolecules on earth, and the source
of immediate energy needs in living systems. Carbohydrates also participate in defining the structure of cells
and living systems. Lipids are nonpolar macromolecules; thus they are insoluble in water. They include oils
and fats, phospholipids (found primarily in the cell membranes of living systems), and steroids (found in
the cell membrane of animals, where it provides structural support). Proteins are polymers of amino acids.
Proteins have numerous biological functions. The common types of proteins that are found in biological
systems are enzymes, antibodies, transport proteins, regulatory proteins, and structural proteins. The fourth
type of organic compound important to structure and function are the nucleotides . A nucleotide is one of a
class of organic compounds composed of three subunits: (1) one or more phosphate groups, (2) a pentose
sugar, and (3) a nitrogen-containing base. Nucleotides can be assembled into nucleic acids (DNA or RNA) or
the energy compound adenosine triphosphate. (Gordon Betts et al. 2013)
OBJECTIVE
In this exercise, you will learn the different biochemical tests to detect the presence of the organic molecules
such as proteins, starches, sugars, and fats.
MATERIAL
You will watch videos demonstrating the different biochemical tests that require the following materials: a
test tube rack, 4 test tubes, 5 transfer pippetes, protective glasses, 3 pieces of paper bag, deionized (DI)
water, evporated milk, 50% egg white, 1% sucrose, 1% starch solution, onion juice, 10% sucrose solution,
vegetable oil, Biuret reagent, Iodine, and Benedict’s reagent.
1
PROCEDURE
Step 1
Watch the video below (1:54 min - 6:17 min) to learn how the test for protein is conducted. Record your
observations and interpretation in Table 1 and answer the Question 1 and 2 in the space provided below.
Link to video: Macromolecular Lab - Proteins and Starches
Question 1
Using biuret reagent. The substances were placed into test tubes where 5 drops of biuret reagent to each test
tube. An indicator of a color for a negative test and purple or pink for positive.
Table 1: Test for proteins.
Contents Results Interpretation
Test tube 1 Deionized Water Blue Positive
Test tube 2 Evaporated Milk Pinkish Purple Positive
Test tube 3 50% Egg white solution Purple Positive
Test tube 4 1% Sucrose Blue Negative
Question 2
Deionized water and 1% sucrose tests negative for proteins because of the blue color indicator.
Step 2
Continue to watch the video above (6:17 min - 8:23 min) to learn how the test for starch is conducted. Record
your observations and interpretation in Table 2 and answer the Question 3 and 4 in the space provided below.
Question 3
The test for starch was conducted using the iodine solution. An iodine solution was mixed with the substances
to observe color change.
Table 2: Test for starches
Contents Results Interpretation
Test tube 1 Deionized water Light yellow negative
Test tube 2 1% starch solution light yellow positive
Test tube 3 onion juice light yellow negative
Test tube 4 1% sucrose light yellow Negative
Question 4
Only the 1% starch solution tested for positive in starch.
2
Step 3
Watch the video below (0:00 min to 2:43 min) to learn how the test for sugar is conducted. Record your
observations and interpretation in Table 3 and answer the Question 5 and 6 in the space provided.
Link to video: Macromolecular Lab - Sugar and Fats
Question 5
Benedict’s reagent was added to the test tubes containing the different solutions and the test tubes placed in
a boiling water bath for 10 minutes to observe color change after.
Table 3: Test for sugar
Contents Results Interpretation
Test tube 1 Deionized water blue negative
Test tube 2 1% starch solution light blue negative
Test tube 3 1% sucrose light blue green positive
Test tube 4 10% sucrose yellow positive
Test tube 5 onion juice dark brown positive
Question 6
The two sucrose solutions tested for positive while the deionized water and starch solution tested negative for
the test for sugar.
Step 4
Continue to watch the video above (2:44 min - 4:55 min) to learn how the test for fats is conducted. Record
your observations and interpretation in Table 4 and answer the Question 7 and 8 in the space provided.
Question 7
The test was conducted by placing drops of the solutions on top of paper bags. The paper bag after 15
minutes was examined for any oily residue in order to determine the presence of fats.
Table 4: Test for fats
Contents Results Interpretation
Paper bag 1 deionized water evaporated negative
Paper bag 2 vegetable oil oily residue positive
Paper bag 3 milk solution oily residue positive
Question 8
Vegetable oil and milk solution cointained fat according to the test while the water did not. This is because
oil is derived from fats and dairy products contain lipids.
3
Step 5
In this section, you will identify the biomolecules present in food. Examine Table 5 that presents simulated
data of the tests (arranged in random) for the presence of biomolecules in six unknowns. Complete Table 6
by indicating the expected results based on the information presented in Table 5. Also, complete Table 7 by
indicating the interpretation of the results based on the information in Table 5 and 6. Hints: (a) Benedict’s
reagent is used in Test 1, (b) Unkown 2 turned purple in Test 2, and (c) protein is present in all Unknowns.
Table 5: Simulated data of tests for biomolecules in six unknowns
Test 1 Test 2 Test 3 Test 4
Unknown 1 - - + +
Unknown 2 - + + +
Unknown 3 - - + +
Unknown 4 + - + +
Unknown 5 + - + +
Unknown 6 + - - +
Table 6: Expected results of the simulation (i.e. color changes or
oily residue)
Test 1 Test 2 Test 3 Test 4
Unknown 1 blue solution light yellow solution oily residue purple solution
Unknown 2 blue solution purple solution oily residue purple solution
Unknown 3 blue solution light yellow solution oily residue purple solution
Unknown 4 brown solution light yellow solution oily residue purple solution
Unknown 5 brown solution light yellow solution oily residue purple solution
Unknown 6 brown solution light yellow solution evaporated purple solution
Table 7: Interpretation of the expected result of the simulation
(i.e. presence/absence of protein, starch, sugar, or fat)
Test 1 Test 2 Test 3 Test 4
Unknown 1 absence of sugar absence of starch presence of fats presence of protein
Unknown 2 absence of sugar presence of starch presence of fats presence of protein
Unknown 3 absence of sugar absence of starch presence of fats presence of protein
Unknown 4 presence of sugar absence of starch presence of fats presence of protein
Unknown 5 presence of sugar absence of starch presence of fats presence of protein
Unknown 6 presence of sugar absence of starch absence of fats presence of protein
Question 9
Test 1 tested for sugars, test 2 tested for starch, test 3 tested for fats, and test 4 for proteins.
Question 10
potato juice is unknown 2 because potatoes contain starch and it tested positive for the presence of starch
4
Question 11
unknown 3 is the egg yolk because egg yolk is mainly composed of fats and proteins.
Question 12
Since it known that diet soda has no sugar. The appropriate test would be to find for sugar. Test 1, as shown
in the experiment, should show a darker shade color of the mixture in order to determine the sugar content
of the substance. The test will be done in order to compare the relative sugar content between the two.
Question 13
water is the negative control in the experiment this is done to make sure how the test would occur when
there is no reaction
REFERENCE
J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana
Korol, Jody E. Johnson, Mark Womble, Peter DeSaix. 2013. Anatomy and Physiology. Houston, Texas:
OpenStax.
Burran S. and DesRochers. 2019. Lab 3: Biological Molecules. URL: https://tinyurl.com/y2vysswe
Center for eLearning. 2016. Macromolecule Lab - Proteins and Starches. Video URL: https://www.youtube.
com/watch?v=LEf-Vch6J-g&feature=youtu.be
Center for eLearning. 2016. Macromolecule Lab - Sugar and Fats. Video URL: https://www.youtube.com/
watch?v=v6QiaI715is
