Membrane Structure 1

GeneralBiologyOnline

Ch. 8 Contents

General
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------------------Online--------------------------------------- Ch. 8 Membrane Structure and Function

1. Membrane Structure

1.1 Phospholipids are the basic building blocks of cell membranes. For a review of Ch. 5 phospholipids,

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The phospholipd above is represented by the symbol below: hydrophilic head & hydrophobic tail.

The basic structure of cellular membranes, shown below, is made of individual phospholipid molecules.

The membrane is "fluid," not ridged, and forms a "semi permeable" barrier around the cell. Semipermeable means small molecules such as oxygen, carbon dioxide and water can pass through the membrane, but larger polar molecules and ions require specific transport proteins (gates) to help them across. The image below (Fig. 8.9 a in text) shows two transport proteins allowing molecules to cross a plasma membrane. The protein on the left simply allows the molecules to diffuse across (passive transport). The molecule on the right uses ATP energy to pump molecules across the membrane (active transport). Active transport is required for molecules that must be moved against their natural diffusion gradient or concentration gradient.

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