Name ________________________
Biology 165 Lab Activity Sheet 2
Macromolecules: Carbohydrates and Lipids
The Structure of Carbohydrates (sugars) and Lipids (fats)
1. Using the octet rule, fill in the following table with the number of covalent bonds each atom
can make in a molecular compound based on its atomic number in parentheses:
CARBON (6)
OXYGEN (8)
HYDROGEN (1)
STUDENT ACTIVITIES:
Sharing a model kit with your table, work together to examine the structures of glucose sugar
and lipids (triglyceride and phospholipid).
A. MODELING GLUCOSE (C6H12O6) - A MONOSACCHARIDE:
Using the color codes below, build a model of glucose.
Model Color Codes:



BLACK - Carbon
RED - Oxygen
WHITE- Hydrogen
1
Instructor initials _________
GLUCOSE CONTINUED:
1. ANSWER THE FOLLOWING QUESTIONS:
a. Observe the arrangement of carbon (C) , oxygen (O), and hydrogen (H) atoms in your
glucose model.
b. On your model, do all atoms appear to make their maximum number of covalent
bonds?
YES
NO
c. Recall how partial charges develop on water molecules. Are there any areas in the
glucose model where partial charges should develop?
YES
NO
d. Glucose is a polar molecule. Label the atoms on the image above that exhibit partial
positive (δ+) and/or partial negative (δ‒) charges.
B. MODELING A LIPID (TRIGLYCERIDE) MOLECULE:
A triglyceride, or fat, molecule consists of three chains of carbon atoms with oxygen only on
one end. Each chain is a fatty acid. The three are connected through a molecule called glycerol.
Model Color Codes:



BLACK - Carbon
RED - Oxygen
WHITE- Hydrogen
2
Procedure:
a. On the figure above, circle the three carbon atoms of the glycerol.
b. Construct your model so that it contains three fatty acid chains.
Instructor initials _____


Note: the exact length of the fatty acid chains may vary among different groups’
models, there is no “absolute” fatty acid length. Each model, however, should
contain three fatty acids of the same length decided by the group.
Note the location of hydrogen atoms on the image and model. In figures, such
as the one above, the location of hydrogen atoms is often depicted as an emptyended stem.
1. ANSWER THE FOLLOWING QUESTIONS:
a. Consider how partial charges develop on water molecules – are there any areas in the
fat molecule where partial charges should develop?
YES
NO
b. How does this affect the behavior of oils in water?
c. Draw a box around the areas on the figure where oxygen atoms form double covalent
bonds. Find these on the model.
c. Draw an arrow on the figure to indicate where a double covalent bond occurs between
carbon atoms.
d. Compare the fatty acids with no carbon double covalent bonds to the fatty acid with the
double covalent bond. How are the shapes of the fatty acid molecules different?
e. How many hydrogens are attached to each of the carbons in a double bond? _______
f. How many hydrogens are attached to each of the carbons elsewhere in the chain?
_______
g. Triglycerides with fatty acid chains that have no double bonds between carbons are
referred to as saturated fats. The presence of double bonds between carbons causes
the triglyceride to be an unsaturated fat.
1. On the triglyceride figure above, circle and label the fatty acids that are
saturated and unsaturated.
3
C. MODELING A PHOSPHOLIPID:
The phospholipid is the primary molecule of all cell membranes. It is based on the triglyceride,
but has a phosphate group in place of the third fatty acid.
Model Color Codes:
a.
b.
c.
d.
e.
BLACK - Carbon
RED - Oxygen
WHITE- Hydrogen
PURPLE - Phosphorus
BLUE - Nitrogen
Procedure:
1. To convert a triglyceride into a phospholipid, remove
the third fatty acid from the glycerol molecule.
2. Attach the nitrogen/phosphorus “head” as depicted in
the image.
3. Phosphorus (P) attached to four oxygen molecules (O) is
known as a “phosphate group” and has the formula
PO4―. The negative charge indicates an extra electron;
it is on the oxygen atom lacking one of its covalent
bonds. Draw a (–) symbol on this oxygen at right.
Instructor initials: ______
4
4. ANSWER THE FOLLOWING QUESTIONS ABOUT PHOSPHOLIPIDS:
a. The phospholipid “head” is considered (circle one):
POLAR
NONPOLAR
b. The fatty acid “tails” are the same as in a
triglyceride. They are considered:
POLAR
NONPOLAR
c. Which do you predict will interact with water molecules, the “head” or the “tails”?
5