Lab Activity Form: Biomolecules

  • with Background Information and Activity Procedures included at the end

Data Sheet: Activity – Biomolecules

Procedure I – Group 1: Known Sample Solutions

Complete the table below using your data from Procedure I. For each sample solution (A-E) indicate any color change that occurs when a test solution is added. Fill in the last column (Biomolecule Classification) using data found under the Activity Form tab.

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Data Table

Sample SolutionTest Solution 1 ReactionTest Solution 2 ReactionTest Solution 3 ReactionTest Solution 4 ReactionTest Solution 5 ReactionBiomolecule Classification
AColor change to redNo reaction.No reaction.No reaction.No reaction.Sugar
BColor change to redColor change to blue.No reaction.No reaction.No reaction.Starch
CNo reaction.No reaction.Color change to green.No reaction.No reaction.Fat
DNo reaction.No reaction.No reaction.Color change to pink.No reaction.Protein
ENo reaction.No reaction.No reaction.Color change to pink.Color change to grey.Amino Acid

Observations and Questions

[1] Write a hypothesis statement for the experiment you conducted for Procedure I.

[2] Which variable represents the independent variable? What information helped you to come to that decision?

[3] Would you characterize this experiment as qualitative or quantitative? What information helped you to come to that decision?

[4] Refer to your completed Data Table I and place the appropriate answer to each of the statements below.

Answers: amino acid, starch, fat, sugar or starch, protein or amino acid

Statements:

Test Solution 1 reacts with:

Test Solution 2 reacts with:

Test Solution 3 reacts with:

Test Solution 4 reacts with:

Test Solution 5 reacts with:

Procedure II – Group 2: Unknown Sample Solutions

Complete the table below using your data from Procedure II. For each sample solution (A-E) indicate any color change that occurs when a test solution is added. Next, use Data Table I to determine the biomolecule classification for each sample solution.  Hint: compare the color changes in both tables to make your determinations.

Data Table II

Sample SolutionTest Solution 1 ReactionTest Solution 2 ReactionTest Solution 3 ReactionTest Solution 4 ReactionTest Solution 5 ReactionBiomolecule Classification
ANo reactionNo reactionNo reactionColor change to pink.Color change to grey. 
BColor change to red.No reactionNo reactionNo reactionNo reaction. 
CNo reaction.No reactionNo reactionColor change to pink.No reaction 
DNo reaction.No reactionColor change to green.No reactionNo reaction 
EColor change to red.Color change to blue.No reactionNo reactionNo reaction 

Observations and Questions

[5] In Procedure II, did any of your unknown sample solutions (A, B, C, D, E) contain sugars? If yes, which one? What information helped you to come to that decision?

[6] In Procedure II, did any of your unknown sample solutions (A, B, C, D, E) contain protein? If yes, which one? What information helped you to come to that decision?

[7] Using the laboratory tests in this experiment, would you be able to distinguish between a small molecule such as amino acid from a larger molecule such as a protein? Explain why or why not.

[8] Using the laboratory tests in this experiment, would you be able to distinguish between a starch and a sugar such as glucose? Explain why or why not.

ACTIVITY PROCEDURE:

Pre-Activity Checklist

Read the background material to help you understand the concepts related to this activity

Activity Procedure

In this activity you will use test solutions to identify biomolecules in two sets of sample solutions (Group 1 and Group 2). In the first procedure (Procedure I ‐ Group 1) the biomolecules present are known for each sample solution (look under the Activity Form tab for details) and you will observe the reaction (color change) for each test solution. In the second procedure (Procedure II ‐ Group 2) you will use the results from Procedure I to determine the biomolecules present in the Group 2 sample solutions.

Procedure I Group 1: Known Sample Solutions

In this procedure you will observe the reaction (color change) when a test solution is added to a sample.

1. select Group 1 by clicking or tapping on its button

2. select Test Solution 1 by clicking on its button

3. click the Start Data Run button and monitor Sample Solutions A-E for color changes

Note: allow 5.00 seconds for the data run to complete ‐ do not interrupt the data run

4. record your observations in Data Table I

6. press the reset button and repeat steps 1-4 for each Test Solution

Procedure II Group 2: Unknown Sample Solutions

In this procedure you will observe the reaction (color change) when a test solution is added to a sample.

1. select Group 2 by clicking or tapping on its button

2. select Test Solution 1 by clicking on its button

3. click the Start Data Run button and monitor Sample Solutions A-E for color changes

Note: allow 5.00 seconds for the data run to complete ‐ do not interrupt the data run

4. record your observations in Data Table II

5. press the reset button and repeat steps 1-4 for each Test Solution

Post-Activity

Use Data Table I to determine the biomolecule classification for each sample solution in Group 2 (in Data Table II).

Learning Objectives

  • Write hypothesis statements based on knowledge of biological principles
  • Identify experimental variables such as the independent, dependent and control variables
  • Distinguish between qualitative and quantitative data
  • Determine the presence of amino acids, proteins, glucose, and starch using indicator solutions
  • Discuss how different biological molecules interact with distinct chemical test reagents
  • Discuss the functional aspects of different chemical functional groups in biological molecules
  • Recognize and identify chemical function groups in biological molecules

Conducting Experiments

The foundation of science knowledge is based on experimentation. Experiments are carefully designed to assure that results can be clearly interpreted. In conducting experiments, it is extremely important that all variables be very precisely defined, measured and controlled. In the laboratory experiments in this course, you will need to identify, measure and control specific variables like a scientist would do.

The first step of an experiment is to come up with a question based on an observation. For example, you might ask “Does the amount of nitrogen in the soil in my garden have an impact on the number of tomatoes on the vine?”. You would then develop a testable hypothesis statement. For example, “I hypothesize that the number of tomatoes in my garden will be low when the content of nitrogen in the soil is low.”

Independent variable

You will set the value of this variable (for example, the amount of nitrogen in the soil) it can be set to different values (for example, nitrogen levels could be low, medium, and high).

Dependent variable

The value of the variable will vary depending the value of the independent variable (for example, the number of tomatoes on the vine will be high when the amount of nitrogen is medium, but the number of tomatoes on the vine will be low when the amount of nitrogen is low and high). The value of this variable is the main experimental result. As part of a hypothesis statement, you would state how the independent variable will impact the dependent variable.

Control variable

You will set these values so that they do not change. By keeping these variables constant, you assure that they do not impact either the independent variable or the dependent variable (for example, if you set up three different test gardens for low, medium and high nitrogen soil levels, you will want to make sure that all three gardens receive the same amount of water and sunlight. In this case, water and sunlight would be the variables that you control.).

Experimental results

Experimental results can be either qualitative or quantitative. In the example above, the experimental result is quantitative because you can count the number of tomatoes; that is, you can quantify the result. If, for example, we defined the dependent variable as the appearance of blotches on the tomatoes then this could be regarded as a qualitative result because we are not quantifying the number of blotches nor the number of tomatoes with blotches. We are simply checking for the presence of blotches. Essentially, we are evaluating the quality of the result.

Biological Molecules

All matter is made of atoms; thus, living beings are also made of atoms and we speak of the chemistry of life. An examination of the periodic table of elements reminds us that chemical elements in certain groups on the left side of the periodic table interact with certain other elements on the right side of the periodic table; for example, sodium chloride NaCl (salt).

Interaction of the elements that form the basis of living organisms is also important. Biological molecules form the basis for the organelles, cells, tissues and organs and interact with elements and other biological molecules through arrangements of elements called functional groups. See the image below of a biomolecule with representative amino and carboxyl functional groups. Note that “R” represents a group of atoms attached to the functional groups; the R group is referred to as a “side chain.”

Sugars (saccharides) have hydroxyl functional groups and aldehyde functional groups. These aldehyde group of saccharides interacts with chemicals in a test solution called Benedict reagent. This test results in a change in color when a specific kind of sugar (called a reducing sugar) is present. Monosaccharides, such as glucose and fructose, are reducing sugars.

Proteins are composed of polymers of amino acids called peptides. There can be many amine/amino functional groups in proteins. These groups interact with chemicals in a test solution called Biuret Test reagent. Note that some peptides function as long-strand molecules rather than as proteins. The amino groups in long strands of peptides can also interact with chemicals in the Biuret Test solution.

Nutritionally speaking, we categorize the macromolecules as carbohydrates (sugars), lipids (fats), and proteins.

Note: Benedict and Biuret testing solutions are mentioned above only as examples. You will in fact use entirely different testing solutions for your lab work.

Orientation to the Biomolecules Lab Activities

Procedure I Overview

Group 1: Known Sample Solutions – In this procedure you will observe the reaction (color change) when different test solutions are added to a set of known sample solutions. This information will be used in the next procedure to determine the types of biomolecules present in a set of unknown sample solutions.

Procedure II Overview

Group 2: Unknown Sample Solutions – In this procedure you will observe the reaction (color change) when different test solutions are added to a set of unknown sample solutions. Using information from the previous procedure you will be able to identify the type of biomolecule present in each unknown sample solution.