Chapter 2 – The Living Cell Membrane 1. What are two functions of the cell membrane? • The two functions of the cell membrane are (1) to separate the cell’s protoplasm from the external environment and (2) to mediate what substances enter and leave the cell. 2. What would happen if something pierced the membrane? • If the cell membrane is pierced the protoplasm would ooze out of the cell. • In some cases it is possible for the membrane to seal itself again. 3. What would happen if cells could not exchange materials with their environment? • Cells need to receive nutrition and gasses from the external environment and excrete their wastes. • If they cannot exchange materials they would quickly either die of starvation or their metabolic wastes would poison them. 4. Describe the composition of the cell membrane. • The cell membrane is composed of 2 layers of phospholipid molecules. Each phospholipid molecule has a hydrophilic “head” and 2 hydrophobic “tails”. • The hydrophillic heads of one layer face the external environment and the heads of the second layer face the internal environment. • The hydrophobic tails are sandwiched between the hydrophillic heads. • A variety of proteins are embedded in the membrane. 5. Which parts of the cell are hydrophobic and hydrophillic? • The polar heads of the phospholipid molecules are hyrophillic. • The tails of the phospholipid molecules are hydrophoic. 6. How are phospholipids arranged in the lipid bilayer? • The tails of the phospholipids face one another and the polar heads face the internal and external environment. 7. What is a glycoprotein and what function do they perform for the cell? • Glycoproteins are proteins found embedded in the lipid bilayer that have a special sugar molecule attached. • They give the cell its unique identity. 8. Describe the three functions of membrane proteins. • Membrane proteins act as “gatekeepers” allowing substances in and out of the cell. • They act as receptor sites for hormones. • They also serve to identify the cell for cell to cell recognition. 9. How are liposomes used in medicine today? • Liposomes are used to treat cancer. • They can bind with the cell membrane and deliver cancer fighting drugs directly to the affected area. 10. What is gene therapy and how is it linked to liposomes? • Gene therapy is the process of introducing new genes into the DNA of a person’s cells to correct a genetic disease or flaw. • Liposomes can be injected with the corrected DNA and they can fuse the to the target (diseased) cell and deliver the corrected DNA.