The Plasma Membrane_{(1 of 9)}

• Transparent barrier for cell contents

• Contains cell contents

• Separates cell contents from surrounding environment

The Plasma Membrane_{(2 of 9)}

• Fluid Mosaic Model is constructed of:

  • Two layers of phospholipids arranged "tail to tail"

  • Cholesterol and proteins scattered among the phospholipids.

  • Sugar groups may be attached to the phospholipids, forming glycolipids.

Figure 3.2 Structure of the Plasma Membrane

Concept Link 1

• Remember, phospholipids are polar molecules: The charged end interacts with water, and the fatty acid chains do not (see Ch. 2, pg. 46). It is this property of polarity that makes phospholipids a good foundation for cell membranes.

The Plasma Membrane_{(3 of 9)}

• Phospholipid arrangement in the plasma membrane:

  • Hydrophilic ("water loving") polar "heads" on the inner and outer surfaces of the membrane.

  • Hydrophobic ("water fearing") nonpolar "tails" form the center (interior) of the membrane.

    • This interior makes the plasma membrane relatively impermeable to most water-soluble molecules

The Plasma Membrane_{(4 of 9)}

• Role of Proteins:

  • Responsible for specialized membrane functions:

    • Enzymes

    • Receptors for hormones or other chemical messengers

    • Transport as channels or carriers

The Plasma Membrane_{(5 of 9)}

• Role of Sugars:

  • Glycoproteins are branched sugars attached to proteins that abut the extracellular space.

  • Glycocalyx is the fuzzy, sticky, sugar-rich area on the cell's surface

Turn and Talk!

• Exploring the Plasma Membrane:

  • Share your understanding of the structure of the plasma membrane, including its composition and the role of the phospholipid bilayer.

  • Discuss the concept of selective permeability and how it relates to the plasma membrane. What types of molecules can pass through the membrane, and what factors influence their passage?

• Level 1 Volume

• Please submit on Schoology!

The Plasma Membrane_{(6 of 9)}

• Cell Membrane Junctions

  • Cells are bound together in three ways:

    • Glycoproteins in the glycocalyx act as an adhesive or cellular glue

    • Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion

    • Special cell membrane functions are formed, which vary structurally depending on their roles

The Plasma Membrane_{(7 of 9)}

• Main types of cell junctions

  • Tight junctions:

    • Impermeable junctions

    • Bind cells together into leak-proof sheets

    • Plasma membranes fuse like a zipper to prevent substances from passing through extracellular space between cells

The Plasma Membrane_{(8 of 9)}

• Main types of cell junctions

  • Desmosomes

    • Anchoring junctions, like rivets, that prevent cells from being pulled apart as a result of mechanical stress

    • Created by button-like thickenings of adjacent plasma membranes

The Plasma Membrane_{(9 of 9)}

• Main types of cell junctions

  • Gap Junctions (communicating junctions)

    • Allow communication between cells

    • Hollow cylinders of proteins (connexons) span the width of the abutting membranes

    • Molecules can travel directly from one cell to the next through these channels