All cells Eukaryote (plant and animal), prokaryote (bacteria and blue green algae) contain an outer cell membrane. In addition many of the structures inside of the cell are made up of unit membrane. In this lesson you will learn the chemical makeup and properties of membranes. 
 
 
Unit membrane:  
 
 

Membranes of all cells  have the same basic structure.  Membranes consist of a lipid bilayer in which are embedded globular proteins, many of which extend across the bilayer and protrude on either side. You may want to go back and review the molecular structure of lipids, and phospholipids which was discussed in miniunit Alpha. Click here. click  

 Even though the lipid bilayer provides the basic structure it has an impermeable nature; therefore,  the proteins are responsible for most membrane functions.  Most membranes are composed of 40 to 50 percent lipids and 60 to 50 percent protein.  Not only does the cell membrane consists of unit membrane but many of the cell's organelles consist of unit membrane. 

Read the pages indicated by B-4 and study behavioral objectives 2 and 3. 

 
           The figure above represents structures found in a unit membrane. Identify the lipid bilayer (light gray circular structures with two tails hanging in the center), various proteins (these may extend through the lipid bilayer or float on either surface), carbohydrate polymers (these may be attached to lipid molecules - glycolipids or to protein molecules - glycoprotein), cholesterol molecules (indicated by the letter E), cytoskeleton (indicated by F the cytoskeleton are actually protein attachments which extend into the cytoplasm). 
 

In your notes draw a figure showing the structure of unit membrane including the following structures: phospholipid bilayer (include the hydrophobic tails and hydrophilic heads), proteins (include both extrinsic and intrinsic), carbohydrates (glycolipid and glycoprotein), cholesterol, pores. The phospholipid layer makes the membrane impervious to water and polar molecules. In your notes explain hydrophilic heads and hydrophobic tails in relation to polar and nonpolar properties. You may want to go back and review nonpolar compounds (lipids) and polar compounds (water) in miniunit alpha.  In your notes fill in the table below indicating  four functions of the cell membrane. 
 

       Membrane Function                                            Describe how function 
                                                                                 is accomplished. 
 

isolation from environment
transport regulation
communication
identification

 

1.  What is meant by a fluid mosaic model? 

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Describe in your notes and give the function for each of the following structures found in the cell membrane listed below: These may be found in your reading assignment. 

    Phospholipid bilayer- include permeability to polar and nonpolar molecules. 
 
    Proteins - include transport of ions, specific molecules, water soluble molecules 
                 - include reception of molecules on the exterior of cell 
                 - include recognition 
 
                  Read the pages indicated by B-3 concerning the immune system. 

    Glycoprotein  - include where located and function 
 
    Cholesterol - include where located and function 
 
    Cytoskeleton - include where located and  function 
 

 2.  How does water pass across  the cell membrane? 

                  a)   through the phospholipid layer 
                  b)   through the cholesterol layer 
                  c)   through pores is the phospholipid layer 
                  d)   through glycoprotein 
                  e)   Both a and d 

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 3. Unit membrane consists of two phospholipid layers. 

           a) true            b) false 
 
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  4. Phospholipid molecules are bounded tightly together. 

            a)  true           b) false 

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  5. Which of the following is not true concerning membrane proteins? 

 a) Proteins located on the surface and extend through the membrane can float 
     through the phospholipid  bilayer. 
 b) Some of the proteins can receive  hormones which will trigger a cellular response 
     (speed up cellular respiration). 
 c) Some of the proteins can regulate which  molecules are allowed  to pass through 
     the phospholipid bilayer. 
 d) The function of protein in membrane is solely support. 

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6. Which  membrane structure indicated in the figure above  perform  the following 
    function? 
 "D" represents the structure it is sitting on, the gray round structure with two tails. 
     a) A                                         d) D 
     b) B                                         e) E 
     c) C                                         f)  F 

Identification tags for cell surface attachment. Your immune system can recognize Salmonella bacterium as a foreign invader and target it for destruction. 
 
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7. Which  membrane structure  indicated in the figure above  perform  the following  
   function? 
 "D" represents the structure it is sitting on, the gray round structure with two tails. 
     a) A                                         d) D 
     b) B                                         e) E 
     c) C                                         f)  F 

Act as a transport vehicle which transports water soluble molecules through the membrane. 

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8. Which  membrane structure  indicated in the figure above  perform  the following 
    function? 
    "D" represents the structure it is sitting on, the gray round structure with two tails. 
     a) A                                         d) D 
     b) B                                         e) E 
     c) C                                         f)  F 

Prevents polar ions such as K+ and Na+ from passing through but allows nonpolar ethanol alcohol pass through. 

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9. Which  membrane structure indicated in the figure above  perform  the following 
    function? 
 "D" represents the structure it is sitting on, the gray round structure with two tails. 
     a) A                                         d) D 
     b) B                                         e) E 
     c) C                                         f)  F 

Strengthen the phospholipid bilayer and make it more flexible and less fluid. 

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10. Which  membrane structure indicated in the figure above  perform  the following 
     function? 
 "D" represents the structure it is sitting on, the gray round structure with two tails. 
     a) A                                         d) D 
     b) B                                         e) E 
     c) C                                         f)  F 
 
Consists of protein filaments which anchor the cell's membrane to various structures in the cytoplasm. 

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You must answer the next question correctly to move to the next page. 

11. Which of the following statements is true due to the fluid nature of cell 
      membranes? 

    a ) Membranes can bud off vesicles and seal up again or fuse with vesicles and 
         smooth out again. 
    b ) Membranes are selectively permeable to certain molecules. 
    c ) Once the protein is established on a membrane it is permanently stationed 
         there. 
 

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