Lesson 4.2 Introduction to the chapter

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Introduction to the lesson

Although many molecules come together to make up the cell membrane, the basic structure is provided by the unique phospholipid molecule. In this lesson you will study the phospholipid molecule. As you go through the lesson, bear in mind the overall purpose of the cell membrane and try to think about why the phospholipid molecule is so well suited for its function.

Reading

Read the section “Drug runners” in your text book on p.73

Thinking it through

• Have you ever heard of a liposome before?
• How does a liposome’s method of drug delivery differ from a tablet?
• Why can a liposome be effective in destroying cancer cells?
• What other uses do liposomes have?
• What is similar between a liposome and a cell?

Introduction to cell membranes

Read the first paragraph underneath the introductory box on liposomes in your textbook (p.73).

Thinking it through

• Where are there membranes in the cell?
• Why is the study of these membranes important?
• What role do membranes play in the cell?
• The most common membrane is the cell surface membrane, which surrounds the outer perimeter of the cell, and the terms "cell membrane" and "cell surface membrane" are often used interchangeably. However, where else are membranes found inside the cell? Would the structure of the membrane that surrounds the nucleus, for example, be the same as the structure of the cell surface membrane?

Phospholopids

Read the section under the heading "Phospholipids" in your text book (p.73 and see Fig.4.2 on p.74).

Study Figure 4.2 on p.74 of your text book:

1. Look at the structure of the phospholipid.
   
   1. Notice the hydrophobic tails and the hydrophilic heads and their relationship with the water.
2. This is a cross section of a spherical micelle.
   
   1. Notice the hydrophilic heads facing outside and the hydrophobic tails facing inside.
3. This diagram shows a bilayer.
   
   1. Again notice the structure – the hydrophilic heads face outwards and the hydrophobic tails meet in the middle.
   2. Why do you think there needs to be bilayer when there is water both inside and outside of a cell or an organelle?

 Definitions and review