Membrane Structure and Function

Key terms: You should be able to define these terms using an example where applicable.

phospholipid bilayer      pinocytosis                   proton pump                 hydrophobic

amphipathic                  hypertonic                   cotransport                   hydrophilic       

fluid mosaic model                                             solution                         exocytosis

Davson and Danielli      diffusion                        solvent                          endocytosis

Gorter and Grendle       osmosis                        solute                           phagocytosis

Robertson                    Singer and Nicholson    facilitated diffusion        hypotonic

receptor-mediated endocytosis                         active transport             isotonic

integral  proteins           concentration gradient   flaccid                          peripheral proteins

                                     selective permeability    bulk transport               

Na+/K+ pump             plasmolysis                   

turgid                            crenated                       familial hypercholesterolemia                            


Review questions.

1. Describe the function of the plasma membrane.

2. Describe the contributions that the following groups or individuals made to the development of  models describing the structure of the plasma membrane: Overton,  Langmuir, Gorter and Grendle, Davson and Danieli,  and Robertson.

3. What problems were there  with the Davson and Danielli  model of membrane structure?  Describe the Singer and Nicholson fluid mosaic model and describe how this model answered the problems of the Davson and Danielli model.

4. Describe what it means for a membrane to be fluid.  What factors contribute to fluidity.

5. Describe the experimental evidence that demonstrated that membrane protein as well as lipids move throughout the bilayer

6. Why must membranes remain fluid to work properly?  What role does cholesterol play in maintaining membrane fluidity?  How can cells adjust membrane composition to maintain fluidity when environmental temperature changes?

7. What are some functions of membrane proteins? Distinguish between the location and function of  peripheral and integral membrane proteins. 

8. What is meant by cell-cell recognition?  How is this important in the functioning of an organism?  What kind of membrane molecules are involved in cell-cell recognition? How is cell-cell recognition important in organ transplant operations?

9. Describe how the size and chemical composition of molecules determines whether a cell membrane is permeable to these molecules.  What role do transport proteins play in altering the normal permeability properties of a membrane?

10.Define diffusion in terms of a concentration gradient.  How does the second law of thermodynamics explain that diffusion is a spontaneous process?

11. What effect does addition of solute have on the free energy of water?  Referring to this effect, explain why water will move from hypotonic solution into a hypertonic solution if the two solutions are separated by a membrane.

12. Define osmosis and predict the direction of water movement based upon difference in solute concentration between the cell and the environment.

13. Using the terms turgid, crenated, lysis, flaccid, and plasmolysis,  (where appropriate) describe the result of placing an animal cell in each of the types of solution: hypertonic, hypotonic, and isotonic.  Do the same for a plant cell.

14. How does facilitated diffusion differ from simple diffusion?  In what ways are the carriers involved in this process similar to enzymes?  How is conformational change involved in one model that attempts to explain how facilitated diffusion occurs?

15. How does active transport differ from facilitated diffusion?  How are they similar? 

16. Using the following terms  (conformational change, ATP hydrolysis, phosphorylation, dephosphorylation); describe how the Na+/K+  pump works.  What is the purpose of this pump? 

17. Describe two specific instances of conformational changes that occur in the ATPase membrane protein during the operation of the Na+/K+ pump.  Describe what stimulates the specific conformational change and the result of the change.

19. Describe how a proton pump and  a  sucrose-H+ carrier molecule  are used in cotransport of sucrose into a cell..

20. Compare and contrast exocytosis and endocytosis.  Differentiate between the three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis.

21. Using LDL as an example, explain how receptor-mediated endocytosis works.  What is the consequence of defective LDL receptors?  What is this condition called.

22. Using diagrams and accompanying explanations, describe the structure of the cell membrane (what molecules it's made up of and how they arranged) according to the fluid mosaic model.   How does the structure of the cell membrane relate to its function?

26. What would be the effect on the cell's endomembrane system  if you gave it a drug that inhibited the process of exocytosis but not the process of endocytosis?

27.  Agree or disagree with the following statements.  Fully defend your answer.

A. The fact that plants actively transport solutes into their root cells from the soil helps to compensate for the fact that plant cells lack an internal skeleton to provide body support.


C. Diffusion is an illustrative example of the operation of the second law of thermodynamics.


E. The presence of proteins in the cell membrane is strictly related to the membrane's function of protecting the contents of the cell and holding the cell's contents in place.

F. The same basic law of science that explains  why molecules diffuse form one place to another explains why atoms bond to one another to form molecules.

G. A genetic defect that resulted in a drastically  decreased ability of a cell to synthesize unsaturated fatty acids would likely have more of an effect on an organism that lived  in an arctic environment than an organism that  lived in a tropical environment.

H. As the temperature of the surrounding environment gets lower, there may be an alteration in the chemical composition of the cell membrane.