Name:_________________________________________________
LAB 6: Chemistry of Life: Carbohydrates, Triglycerides and Proteins
Background:
Today, scientists use a combination of biology and chemistry for their understanding of life and life processes. Thus, an
understanding of some chemistry of living things is necessary. Carbohydrates make up a large group of chemical compounds
found in cells. Carbohydrates are an energy source or are used in making cell structures. Triglycerides (fats), a type of lipid,
are present in all living organisms. These chemicals make up certain parts of your body. Fats are often stored when present in
excess and can be used as an energy source. Fats are an important part of our diet. Proteins make up the bulk of solid material
within your body and the bodies of other animals. Your muscle, skin, hair and inside organs are largely are largely protein.
Proteins are essential for growth and repair. They also make up some hormones which function in chemical control of the
body.
Objectives:
 Write a simple formula and read a structural formula for several carbohydrates
 Use models to construct the three main types of carbohydrates.
 Recognize that fat molecules are made up of two kinds of smaller molecules, glycerol and fatty acids.
 Use structural formulas and models of glycerol and fatty acids to determine how these molecules join to form fat
molecules.
 Recognize simple formulas for amino acids.
 Use models of different amino acids to construct a protein molecule.
Materials:
Pencil, paper models & scissors
Pre-Lab Questions: Water Model
1.
What elements make up water?
2.
What does the number 2 following H tell you?
3.
Why does the oxygen symbol, (O), not have a subscript?
4.
How many molecules of water are represented by the formula H2O?
5.
What information is contained in a simple formula? What is the simple formula of water?
6.
What is a structural formula? What is the structural formula of water?
7.
What do the lines between O and H in the structural formula of water represent?
8.
A paper model of water is shown below. We will use this way of representing water throughout the study of different
chemical compounds found in different living systems. Apply your knowledge of bond formation to explain why the
model shows water composed of an H atom and an OH group?
PART I: Carbohydrates
There are three different groups of carbohydrates. They are called monosaccharides, disaccharides, and polysaccharides.
“Saccharide” means sugar.
Group 1: Monosaccharides (single-molecule sugars)
A single sugar is called a monosaccharide.. The prefix –mono means one. However, the one molecule can have different
shapes due to a different arrangement of atoms. Three monosaccharides are glucose, fructose and galactose. Examine the
structural formula of these three sugars shown below and answer questions 1 to 6.
1.
What three chemical elements are present in the three monosaccharides shown?
2.
How many atoms of carbon are present in a molecule of:
Glucose? __________
3.
Galactose? __________
Add subscripts to the following to indicate the proper structural formula. Fill in the blanks by calculating the total
number of carbon, hydrogen and oxygen in each molecule.
Glucose: C___H___O___
4.
Fructose? __________
Fructose: C___H___O___
Galactose: C___H___O___
Are there two times as many hydrogen atoms as oxygen in a molecule of:
Glucose? __________
Fructose? __________
Galactose? __________
5.
Are there two times as many hydrogen atoms as oxygen atoms in a molecule of water? _________________
6.
Compare the structural formula of glucose to fructose:
Are they exactly the same shape?________________
Are they both monosaccharides? _________________
Group 2: Disaccharides
Two monosaccharide sugar molecules can join chemically to form a larger carbohydrate molecule called a double-sugar, or
disaccharide. The prefix “di-“ means two. By chemically joining a glucose molecule with a fructose molecule, a double sugar
called sucrose is produced.
7.
Do the glucose and fructose fit together easily to form a sucrose molecule? ___________________
In order to join the molecules, remove an –OH end from one molecule and an –H end from another. Cut along the dotted
lines. (Models fit together like puzzle parts.)
8.
Does removing the –H and –OH now allow the molecules to fit easily together? ___________________
9.
The –H and –OH ends that were removed can also fit together with each other to form a molecule. This new molecule
has a simple chemical formula of _______________ and is called ________________________________________.
10. Write the simple formula for sucrose by adding together the molecular formula s for glucose and fructose and then
subtracting a water (H2O). (Use formulas for this step, not the models.) __________________________________
Joining other monosaccharides in different combinations can make different disaccharide molecules. By chemically joining a
glucose molecule with another glucose molecule, a double-sugar called maltose is formed.
Cut out and attempt to join the two new glucose model molecules like puzzle pieces.
11. What must be removed from the glucose model molecules so that they easily fit together? ____________________________
12. Write the simple formula for maltose. ____________________________
13. a) How does the simple formula for sucrose compare to the formula for maltose? ______________________________________
b) Are there two times as many hydrogen atoms as oxygen atoms in a disaccharide? ________________________
c) How many monosaccharide molecules are needed to form one sucrose molecule? ________________________
d) How many monosaccharide molecules are needed to form one maltose molecule? ________________________
Group 3: Polysaccharides (many molecule sugars)
Just as double sugars were formed from two single sugar molecules, polysaccharides are formed when many single sugars are
joined chemically. The prefix “poly-“ means many. Starch, glycogen, and cellulose are the three most common polysaccharides in
biology. They consist of long chains of joined glucose molecules.
Construct a starch molecule by joining three glucose molecules. This model will represent only a small portion of a starch
molecule because starch consists of hundreds of glucose molecules.
14. What must be removed from the glucose model molecules in order to have them easily fit together?
_____________________________
The simple formula for a polysaccharide is written as (C6H10O5)n. The “n” equals the number of times the C6H10O5 group is
repeated. You can see this group as the middle glucose of your model. REMEMBER: The –H and –OH ends of the middle molecule
are missing.
PART II: Triglycerides
To better understand the chemistry of fats, it is helpful to study first the small molecules, which join to make up trigylcerides, or
fats. Fat molecules are made up of two small “building blocks” or chemical molecules. These molecules are called glycerol and
fatty acids.
Glycerol
The structural formula of glycerol is shown below.
Glycerol
1.
What elements are present in glycerol? ________________________________________________________
2.
Are there any elements in glycerol that are not in carbohydrates? _____________________
3.
What is the simple formula for glycerol? C___H___O___
4.
Are there two times as many hydrogen atoms than oxygen atoms in glycerol? __________________
Fatty Acids
The second kind of molecule that is part of a fat is a fatty acid. Many different kinds of fatty acids exist, but all are similar in
several ways. Butyric acid, caproic acid, and lauric acid are examples of fatty acids. The structural formula for these fatty acids is
shown below.
Butyric Acid
Caproic Acid
Lauric Acid
5.
What elements are present in all fatty acids?__________________________________________________________________
6.
What is the simple formula for butyric fatty acid? C___H___O___
7.
What is the simple formula for caproic fatty acid? C___H___O___
8.
What is the simple formula for lauric fatty acid? C___H___O___
9.
Note the end of butyric acid containing the oxygen atoms. This special arrangement of
carbon, hydrogen and oxygen is called a carboxyl group. Is the carboxyl group present
in all fatty acids? ______________
Carboxyl Group
10. a. List a similarity between glycerol and fatty acids.
b. Do fatty acids and glycerol both contain a carboxyl group? _______________
Combining Glycerol and Fatty Acids to Make a Triglyceride (Fat)
A fat molecule consists of one glycerol molecule and three fatty acid molecules joined.
Cut out the glycerol and fatty acid paper model. Cut along the solid lines only. Attempt to construct a fat molecules.
11. Will the fat molecules fit together as pieces in a puzzle? ________________
Remove three –OH ends from the glycerol molecule and three –H ends from the fatty acids. Now join the molecules to form a
fat.
12. a. How many glycerol molecules are needed to form a fat molecule? ______________
b. How many fatty acid molecules are needed to form a fat molecule? ______________
Join the leftover –H and –OH ends from your models.
13. What chemical substance is formed when the –H and –OH ends are joined? ___________________________________
Production of a fat molecule is a chemical reaction. A chemical shorthand way of expressing the formation of a triglyceride fat
is as follows.
Glycerol + Fatty Acid Molecules  Triglyceride Fat + Water
14. How many water molecules are formed when one fat molecule is produced? ___________________
Many fats exist in living things. Different combinations of fatty acid molecules result in this wide variety of fats.
15. A change in the type of fatty acid results in a different type of fat molecule. What molecule remains unchanged in all
fats? _______________________________________
PART III: Proteins
Proteins are complex molecules made up of smaller molecules called amino acids. There are about 20 different amino acids found
in nature. The element nitrogen (N) is present in all amino acids. Examine the structural formulas of the four representative
amino acids shown in Figure 1.
Glycine
Alanine
Valine
Threonine
1.
Name the four elements present in these amino acids. _____________________________________________________________________
2.
What is the simple formulaf or the amino acid:
Glycine: C___H___O___N___
Alanine: C___H___O___N___
Valine: C___H___O___N___
Threonine: C___H___O___N___
3.
How do the simple formulas for all of the amino acids differ? _____________________________________________________________
____________________________________________________________________________________________________________________________________
Note the upper right hand corner of each amino acid. These ends have a special arrangement of carbon, hydrogen and
oxygen atoms. This end arrangement is called a carboxyl group and looks like this:
Carboxyl Group
4.
Circle the carboxyl group on each structural formulas above. Note the upper left corner of each amino acid. These
ends have a special arrangement of nitrogen and hydrogen atoms. The end arrangement is called an amino group and
looks like this:
Amino Group
5.
Put a square around the amino groups on the structural formulas above.
6.
Do carbohydrates contain carboxyl groups? ______________ Amino groups? _________________
7.
How does the number of hydrogen atoms compare to the number of oxygen atoms in each amino acid?
____________________________________________________________________________________________________________________________
Cut out the four amino acid models. Attempt to join the amino acids.
8.
Can the amino acids easily join to form a protein molecule? _________________________
Join the molecules by removing as man –OH groups and –H groups as needed from the amino acids. All four amino acid
molecules can be joined in this manner to form a protein. Join them in the order valine-threonine-alanine-glycine.
Join the leftover –OH and –H ends.
9.
What chemical substance is formed when the –OH and –H’s are joined? _________________________
10. How many molecules of water are formed when four amino acids join? __________________________
11. What type of chemical compound is formed when the four amino acids join? ____________________________________
12. Describe the relationship between an amino acid molecule and a protein molecule:
______________________________________________________________________________________________________________________________
13. Construct two proteins different from the one you made above. List the order of amino acids here:
a.
______________________________________________________________________________________________________________________
b.
______________________________________________________________________________________________________________________
Figure 1: Sucrose + Water (formed from dehydration synthesis of fructose & glucose)
Figure 2: Maltose + Water (formed from dehydration synthesis of 2 glucose molecules)
Figure 3: Representation of Starch (formed from dehydration synthesis of 3 glucose molecules)
Figure 4: Triglyceride (fat) Molecule (made from dehydration synthesis of a glycerol and 3 fatty acids)
Figure 5: Representation of a Protein Molecule (made from dehydration synthesis of 4 amino acids)