The Plasma The Plasma MembraneMembrane

The Plasma MembraneThe Plasma Membrane

The cell membrane functions as a The cell membrane functions as a semi-permeable barrier: semi-permeable barrier: allows a few molecules to pass allows a few molecules to pass

through while preventing the passage through while preventing the passage of others either from the outside in or of others either from the outside in or from the inside outfrom the inside out

Membrane StructureMembrane Structure

The membrane is composed of a The membrane is composed of a phospholipid bilayerphospholipid bilayer

Structure of a phospholipid:Structure of a phospholipid: polar head polar head

hydrophilic (like water)hydrophilic (like water) two non-polar tails two non-polar tails

hydrophobic (fear water) hydrophobic (fear water)

PhospholipidsPhospholipids

Phospholipids are aligned tail to tail so Phospholipids are aligned tail to tail so that the non-polar areas form a that the non-polar areas form a hydrophobic region between the hydrophobic region between the hydrophilic heads on the inner and hydrophilic heads on the inner and outer surfaces of the membrane.outer surfaces of the membrane.

This layering is termed a bilayer and This layering is termed a bilayer and called a phospholipid bilayer in the case called a phospholipid bilayer in the case of the cell membraneof the cell membrane

The Fluid-Mosaic ModelThe Fluid-Mosaic Model

Fluid-mosaic model describes the Fluid-mosaic model describes the fluid nature of the membrane and fluid nature of the membrane and its compositionits composition

Fluid PortionFluid Portion Membrane behaves like a fluidMembrane behaves like a fluid

Due to the phospholipidsDue to the phospholipids Consistency ranges from oil to a gel like Consistency ranges from oil to a gel like

semi-solidsemi-solid animationanimation

The Fluid-Mosaic ModelThe Fluid-Mosaic Model

Mosaic PortionMosaic Portion Just like a piece of Just like a piece of

mosaic tile art, mosaic tile art, the membrane the membrane contains several contains several different different structures that structures that perform a variety perform a variety of functionsof functions

The Fluid-Mosaic ModelThe Fluid-Mosaic Model

Other structures found in the Other structures found in the membrane membrane Proteins:Proteins: involved in transporting involved in transporting

materials inside and out of the cellmaterials inside and out of the cell Carbohydrates:Carbohydrates:used to identify used to identify

substances that come in contact with substances that come in contact with the cellthe cell

Cholesterol:Cholesterol: a steroid used to help a steroid used to help stabilize the membranestabilize the membrane

The Fluid-Mosaic ModelThe Fluid-Mosaic Model