The Plasma Membrane: A Transparent Barrier

The Plasma Membrane:

A Transparent Barrier that maintains Homeostasis.

By: Grecia Medina

Open Ended

• What can you remember about the membrane of a cell?

The Plasma Membrane_{(1 of 9)}

• Transparent barrier for cell contents

• Contains cell contents

• Separates cell contents from surrounding environment

Multiple Choice

What is the main purpose of the cell membrane?

• To separate the cell contents from the surrounding environment

• To interact with water through the polar heads of phospholipids

• To contain cell contents and regulate the movement of substances

• To arrange phospholipids 'tail to tail'

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.

Open Ended

• What is it mainly made up of? How does it interact with water?

Multiple Choice

What is the model that makes up the plasma membrane?

• The Foundation Model

• The Water Model

• The plasma membrane model

• The Fluid Mosaic Model

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

Multiple Choice

How is the plasma membrane arranged?

• In one layer, with the "polar tails" on the outside and the "nonpolar heads" on the inside.

• In one layer, with the "polar heads" on the outside and the "nonpolar tails" on the inside.

• In two layers, with the "polar heads" on the outside and the "nonpolar tails" on the inside.

• In two layers, with the "polar tails" on the outside and the "nonpolar heads" on the inside.

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

Multiple Choice

What is the role of proteins in the Plasma Membrane?

• To divide the DNA.

• Helps to breakdown carbohydrates.

• Gets water into the cell.

• • Responsible for specialized membrane functions

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

Multiple Select

What are the different types of cell junctions?

• • 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

• • Responsible for specialized membrane functions

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

Multiple Select

What are the three ways that cells are bound together?

• • Tight Junctions

• • Desmosomes

• • Gap Junctions

• • Connexons

Open Ended

• Why do phospholipids (which form the bulk of plasma membranes) organize into a bilayer, tail to tail, in a watery environment?

Open Ended

• The external faces of some membrane proteins have sugar groups attached to them. what are three roles these sugar-coated proteins play in the life of a cell?

Open Ended

• What is the special function of gap junctions? Of tight junctions?