Cell Membrane Activity
Background:
If a cell membrane is viewed in cross section, it looks like the picture on the back of this paper. Both the
cell’s exterior and interior membrane face water. The shape of the cell membrane is of two layers of
phospholipids sandwiched together. How do these molecules make the cell membrane? How do these
molecules arrange themselves so that the cell membrane is held together?
It turns out that the phospholipid molecules contain two regions (see diagram below). The glycerol
“head” of the phospholipid molecule is polar and attracts toward water. This attraction is considered
water-loving or HYDROPHILIC. In contrast, the fatty acid “tail” of the phospholipid molecule is nonpolar and moves away from water. This is considered water-fearing or HYDROPHOBIC. Figure 1 below
is a phospholipid molecule.
] “head” (polar region)
] “tail” (non-polar region)
Several proteins are also included in a cell membrane, including marker proteins (with a carbohydrate
chain that acts like a name tag for the cell), channel proteins (which allow charged molecules to diffuse
between the cell interior and cell exterior), protein pumps (embedded in the cell membrane for structural
support, communication, metabolism and basic transport needs) and enzymes (these proteins may span
the entire membrane or partway into it and are ready to accept substrates/signals). Protein positions
within the cell membrane depend on their hydrophobic and hydrophilic regions.
Hydrophilic
Hydrophobic
Hydrophilic
Channel Protein
Enzyme
Protein Pump
Marker Protein with
carbohydrate chain
Directions: Follow the directions below to generate a fluid mosaic model of a generic cell membrane
cross section. Use the cell cross section on the back of this paper. Read all directions so that you can plan
your drawing before starting to draw and label. Use a pencil to start!
1. Using the Background information as a guide, label all regions which contain WATER.
2. Draw several (10-20) phospholipid molecules forming a lipid bilayer within the cell membrane
cross section.
3. Label the polar and non-polar regions of the cell membrane.
4. Label the hydrophilic and hydrophobic regions of the cell membrane.
5. Draw two of each protein shown/listed above and two enzymes using the diagram as a guide.
Decide which way each protein will face. Make sure to label each one.
6. Fill in the rest of the cell with phospholipids. Make sure there are NO SPACES between the
molecules in your membrane! If there are any spaces/holes your cell will leak all of its contents or a
bacteria/virus will enter and your cell will die! (earning you a 0).
7. Research 1-3 additional molecules that may be in a cell membrane. List the structure and function
of these under your membrane. Draw them within the membrane.
8. Color your drawing.
Name_________________________________________Date___________________Hour__________
Diagram of Cell Membrane in cross section.
Cell Exterior
Cell Interior
Additional cell membrane molecules: