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Molecules of Life (Team 4)

Page history last edited by Karen Huang 10 years, 2 months ago

A. Learning Objectives

In this lab, students will:

• identify the presence of various macromolecules due to their structural properties.

• determine the identity of unknown food products based on their molecular make-up.


B. Textbook Correlation: 

Please review  Sections 3.2-3.5 of Chapter 3: Organic Molecules when preparing for the lab.


C.  Introduction:

Cells are the basic unit of life.  In order to understand the nature of cells, we have to appreciate their chemical make-up.  The four most abundant elements of life include oxygen, carbon, hydrogen and nitrogen.  These elements make up 96% of your body and can be organized into molecules through chemical bonding.  An example of a molecule that is essential in supporting life is H2O, otherwise known as water.  Other examples of biologically important molecules include amino acids, fatty acids, monosaccharides, and nucleotides.  These four molecules are the basic building blocks of the macromolecules used to construct our cells.  There are four types of macromolecules found within all cells:  carbohydrates, lipids, proteins, and nucleic acids.  These organic (carbon-containing) macromolecules are organized into a functional unit we call cells.  In this exercise, we will analyze the properties of the following macronutrients (required in large amounts): water, carbohydrates, lipids, and proteins. 


D.  Unknown Food Project

Throughout your introductions, you have emphasized the importance of macronutrients on our health and discussed the food products that contain each type.  We often classify food groups based on their nutrient content.   The goal is to determine the identity of the four unknown food products based on the nutrient make-up of each.   While certainly these unknowns may have more than one of the nutrients listed below, each food products is representative of each class of macromolecules. 


To accomplish this goal, you will have to devise experiments to detect the presence of these nutrients.  Below is a list of materials that will be available:

1. Test Tubes

2.  Plastic droppers

3. Hot plate and beaker of water containing boiling chips

4. Distilled H2O

5. Known food products: glucose, starch, egg, and vegetable oil

6. Chemical reagents for testing.  In the list of reagents below, I have included the volumetric ratio of test substance/reagent for each and included the order by which materials should be added to their respective tubes:

     a.  Biuret reagent: 20 drops (1mL) test substance/10 drops (0.5mL) of reagent

     b.  Lugol's solution: 60 drops (3 mL) test substance/10 drops (0.5 mL) of reagent

     c.  Benedict's solution:  40 drops (2 mL) test substance/40 drops (2 mL) of reagent

     d.  Sudan reagent:  60 drops (3 mL) of water/60 drops (3 mL) of test solution/10 drops (0.5 mL) of reagent/40 drops (2 mL) of water


Your job is to research these reagents before lab to determine the appropriate use for each.  You also need to determine if there are any special condition necessary (i.e. heat, pH) that are necessary.  You also need to specify the negative and positive control for each experiment.


In the space provided below outline the experiment you will use to detect the presence of each nutrient in the four unknown food products.  After the experimental section, you will record your data and write a conclusion for each experiment (i.e. which nutrient(s) was present in each unknown). 


A.  Simple Carbohydrates:

Experimental Design (outline the procedure for identifying simple sugars HERE.  Make sure to include both a negative and positive control.

Simple carbohydrates are simple sugars, meaning they are monosaccharides or disaccahrides. Benedict's reagent can be used to test for glucose and many other simple sugars. If after adding Benedict's Reagent into the unknown substance, the solution turns green, yellow or red, then the unknown substance contains simple sugars. If after the addition of Benedict's Reagent, the unknown substance remains clear or is a little blue, then the test is negative for simple sugars. 




B.  Complex Carbohydrates:

Experimental Design (outline the procedure for identifying complex sugars HERE.  Make sure to include both a negative and positive control.): 

 Complex carbohydrates, also referred to as 'starchy' foods, are carbohydrates with three or more sugars. Lugol's solution is used to test for such starches, and will not detect simple carbohydrates. In the presence of complex carbohydrates, the iodine in Lugol's solution will react with the coil structure of the polysaccharide by staining the starch a dark blue/black color, indicating a positive result. However if there is no dark blue/black staining after Lugol's solution is added to a substance, then it signifies that there is a negative result for starches/complex carbohydrates.




C.  Proteins:

Experimental Design (outline the procedure for identifying proteins HERE.  Make sure to include both a negative and positive control.):  

Proteins are polymers of amino acids. Amino acids join together to form peptides through peptide bonds, which later through dehydration synthesis form polypeptides. The Biuret Reagent is used for detecting peptide bonds. This means that it can detect the presence of proteins in a substance since proteins are made up from peptide bonds. The Biuret Reagent can be added to an unknown substance and if the solution turns from blue to purple then it contains proteins however if it remains the same, that indicates that the substance is negative for proteins. 





D.  Fats:

Experimental Design (outline the procedure for identifying fats HERE.  Make sure to include both a negative and positive control.):   

With Sudan reagent you can test for lipids. They have a high affinity to fats. The unknown substance will react with the Sudan reagent and change colors if lipids are present. It will change to an orange-red and the more concentrated the color the more concentrated the lipids are in the sample. In a negative effect there will be no change or reaction and it will remain the same. We will use water as our negative control.

Another test we will preform is where you put 2 drops onto a brown paper bag or pieces of it. If the bag becomes translucent it means there are lipids in the solution placed onto it.






E. Results and Conclusions

Please embed the presentation on the lab using the instructions provided in the syllabus.



Hi Team 1 and Dr. Weber, Here is our VoiceThread for Lab 3, Molecules of Life. Enjoy~ :D





Color Before Heating

Color After Heating

a.      distilled water



b.      glucose



c.       lactose



d.      starch



e.      orange juice



f.        soda



g.      diet soda



h.      unknown substance A



i.        unknown substance B



j.        unknown substance C



k.       unknown substance D




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