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 non-polar 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.

Channel Protein EnzymeProtein PumpMarker 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: