Cells and Tissues (A&P)

Chapter 3 (August 20)

What are the 3 functions of the plasma membrane?

• transparent barrier

• contains cell contents

• separates cell contents from surrounding environment

What are the 4 components/parts of the plasma membrane?

• Phospholipids

• Cholesterol

• Proteins

• Sugars

What is the cell membrane structure and arrangement referred to as?

Fluid Mosaic Model

How are phospholipids arranged in the plasma membrane?

Arranged in 2 parts:

• Hydrophilic (water loving) Polar Heads

  • oriented on the inner and outer surfaces of the membrane

• Hydrophobic (water hating) Polar Tails

  • form the center (interior) of the membrane

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

Why is the plasma membrane impermeable to most water-soluble molecules?

It is made of hydrophobic tails (interior)

What is the function of cholesterol in the cell membrane?

It stabilizes the bilayer (sticks the layers together) and keeps it flexible

What is the function of membrane proteins in the cell membrane?

• Responsible for specialized functions

• Serve as enzymes

• Receptors for hormones

• Transport (channels/carriers)

What is the function of membrane sugars in the cell membrane?

• also called glycocalyx

• protection

• immunity to infection

• defense against cancer

• transport compatibility

• cell adhesion

• embryonic development

What is glycocalyx?

the fuzzy, sticky, sugar-rich area on the cell’s surface

What are the two components that make up glycocalyx?

• Glycoproteins

• Glycolipids

Glycoproteins (describe)

branched sugars attached to proteins that are found in the extracellular space

Glycolipids (describe)

lipids that contain one or more carbohydrate groups

How are cells bound together?

3 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-grove fashion

• special membrane junctions are formed, which vary structurally depending on their roles

What are the 3 types of membrane junctions?

• Tight junctions

• Desmosomes

• Gap Junctions

Tight Junctions (describe)

• impermeable junctions

• bind cells together into leak proof sheets

• prevent substances from passing through extracellular space between cells

Desmosomes (describe)

• anchoring junctions that prevent cells from being pulled apart as a result of mechanical stress

• created by button-like thickenings of adjacent plasma membranes

• form internal system of strong “guy wires”

Gap Junctions (describe)

• 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 connexon channels