LAB: Molecules of Life--- Carbohydrates
Student Name: ____________________________
Date:______
Background: Biologists today depend up chemistry for much of their understanding of life and life processes. It is important to
have an understanding of some chemical concepts important to living things. Carbohydrates, lipids and proteins are the 3
major groups of organic compounds found in living organisms. Carbohydrates are the focus for today. Carbohydrates are
generally used for energy or cell structures. Today you will be doing the following:

Build on information about water to infer ideas about carbohydrates. Construct 3-d models of
carbohydrates. Simulate dehydration reactions to join monosaccharides together to make disaccharides.
Determine molecular characteristics, such as molecular formulas and structural formulas, of carbohydrates.
Procedure: Work in pairs and pick up a model kit. Follow the key below for the pieces in the kit. Each student is to hand in
their own lab paper. Carbon (black) Oxygen (red) Hydrogen (white) Nitrogen (blue)
Part 1: WATER: The chemical formula of water is H2O. Be examining the formula, some information can be gathered.
Determine the following:
1.
2.
3.
4.
5.
6.
7.
What elements make up water? ______________________________________
What does the subscript number 2 following the “H” represent? _____________
Why doesn’t the have “O” have a subscript? _____________________________
How many molecules of water are represented by the following formula: 3H2O? ______
What is the molecular formula for water? ________________________________
What information can we determine from a molecular formula? ______________
Build a structural formula of water with the parts provided in your kit, and then draw the structural formula of
water in the space below:
8.
How is a structural formula different than a molecular formula?_________________
9.
What do the lines between the “O” and “H” represent? _______________________
----------------------------------------------------------------------------------------------------------------------------------------------------Part 2: CARBOHDYRATES: An important group of biological compounds are the carbohydrates. Carbohydrates contain
Carbon, Hydrogen and Oxygen. The many different types of carbohydrates have been grouped into 3 main categories:
monosaccharides, disaccharides and polysaccharides.
A.
Monosaccharides (single sugars)--- Study the structural formulas for the 3 monosaccharides shown in Figure 1 and
answer the questions that follow.
Figure 1
1.
2.
3.
4.
5.
How many atoms of C are there in each molecule of glucose? _____Fructose? _____ and galactose? ____
Write the molecular formulas for glucose__________ fructose___________ and galactose_______________.
Compare the number of hydrogen atoms to the number of oxygen atoms in each sugar. What is the ratio of hydrogen
to oxygen? (ie, how many H atoms are there for each O atom) _________
How does the ratio of “H” to “O” atoms in the sugars compare to the ratio of “H” to “O” atoms in water? (is it the
same, or is it different?) ______________________________
Now, in your group build a 3-D model of glucose and fructose using the pieces provided. (it might help to pull out the
pieces you need BEFORE starting) Show to Ms. D when you have them built: __________
B.
Disaccharides (double sugars): Two monosaccharide molecules can chemically join together to form a larger
carbohydrate called a disaccharide or double sugar. When a glucose joins with another glucose, a disaccharide
named maltose is formed. When a glucose joins with a fructose, a disaccharide named sucrose is formed. Complete
the following:
1.
2.
3.
4.
5.
Attempt to join your glucose and fructose together to make sucrose. In order to join them, there must be open
bonds. Is it possible to join the 2 sugars together? ____________
To join 2 sugars, a “dehydration reaction” must occur. A dehydration reaction is a loss of water. Remove an
“OH” from one of the sugars, and an “H” from the other sugar. Can you now join the 2 sugars together with the
open bonds? ___________
The “H” and “OH” that were removed from the 2 sugars can also bond together. When they join, you end up
with a molecule of ________________.
Show Ms. D your sucrose model for approval: _________________
Determine the molecular formula for sucrose. (Remember, you added 2 sugars together, but then removed one
water) Show your work:
Final molecular formula for sucrose: _________________________
6.
7.
8.
C.
Maltose is a disaccharide made of 2 glucoses. Explain why the formula of maltose would be EXACTLY the same
as sucrose_____________________________________________________________
What are the ratios of “H” to “O” in the disaccharides? ___________________ How does this ratio compare to
the monosaccharides and to water? ______________________
How many monosaccharides must bond in order to form a disaccharide molecule? __________
Polysaccharides (complex or “many” sugars): Complex sugars are formed when many single sugars are joined
together chemically. 2 common polysaccharides in biology are starch and cellulose. Do the following with another
group:
1. Join your disaccharides together to make a 4-carbohydrate chain. What must you remove in order to join the
sugars together? ____________ For the total of 4 sugars joined, how many total waters were formed? __________
2. Show Ms. D your completed 4-carbohydrate chain. ________________
ANALYSIS: Answer the following questions with your partner:
1.If 50 monosaccharides are joined together, how many waters would be formed? ____________
2. The word carbohydrate is derived from carbon and water (hydrate.) Explain why this combination correctly describes this
chemical group.
3. “Synthesis” means the “process by which simple compounds are united to form more complex materials.” Dehydration
means “loss of water.” Explain why chemists refer to the joining of monosaccharide molecules to form disaccharides as a
dehydration reaction.
4. Look up the term “Isomer” in your glossary. Explain why glucose, fructose and galactose are isomers of each other.
5. Complete the formulas for the following monosaccharides based on your knowledge of ratios:
a. C4H_ O_
b. C_ H10 O_
c. C_H_ O3