The Plasma Membrane

The cell membrane functions as a semi- permeable barrier: The cell membrane functions as a semi- permeable barrier: allows a few molecules to pass through while preventing the passage of others either from the outside in or from the inside out allows a few molecules to pass through while preventing the passage of others either from the outside in or from the inside out

Membrane Structure The membrane is composed of a phospholipid bilayer The membrane is composed of a phospholipid bilayer Structure of a phospholipid: Structure of a phospholipid: polar head hydrophilic (like water) polar head hydrophilic (like water) two non-polar tails hydrophobic (fear water) two non-polar tails hydrophobic (fear water)

Phospholipids Phospholipids are aligned tail to tail so that the non-polar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. Phospholipids are aligned tail to tail so that the non-polar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. This layering is termed a bilayer and called a phospholipid bilayer in the case of the cell membrane This layering is termed a bilayer and called a phospholipid bilayer in the case of the cell membrane

The Fluid-Mosaic Model Fluid-mosaic model describes the fluid nature of the membrane and its composition Fluid-mosaic model describes the fluid nature of the membrane and its composition Fluid Portion Fluid Portion Membrane behaves like a fluid Membrane behaves like a fluid Due to the phospholipids Due to the phospholipids Consistency ranges from oil to a gel like semi- solid Consistency ranges from oil to a gel like semi- solid animation animation animation

The Fluid-Mosaic Model Mosaic Portion Mosaic Portion Just like a piece of mosaic tile art, the membrane contains several different structures that perform a variety of functions Just like a piece of mosaic tile art, the membrane contains several different structures that perform a variety of functions

The Fluid-Mosaic Model Other structures found in the membrane Other structures found in the membrane Proteins: involved in transporting materials inside and out of the cell Proteins: involved in transporting materials inside and out of the cell Carbohydrates:used to identify substances that come in contact with the cell Carbohydrates:used to identify substances that come in contact with the cell Cholesterol: a steroid used to help stabilize the membrane Cholesterol: a steroid used to help stabilize the membrane

The Fluid-Mosaic Model