Plasma (Cell) Membrane

The plasma membrane provides a barrier

between the internal components of a cell

and its external environment.

Homeostasis

• The plasma membrane is the key to maintaining an equilibrium between internal and external conditions.

• Homeostasis is necessary to create conditions suitable for life.

A type of lipids called phospholipids

compose the primary components of the

cell membrane

The phospholipids in the plasma

membrane have a glycerol backbone,

two fatty acid chains, and a phosphate.

The two fatty acid tails of the

phospholipids are nonpolar, the head of

the phosphate is polar.

Water on the outside of the membrane is polar, which attracts the head

of the phosphate turning the tails inside

toward each other forming a bilayer.

Bilayer Structure

• Composed of a double layer (bilayer) of phospholipids

• Phospholipid is made up of hydrophilic and hydrophobic ends

The plasma membrane is

water insoluble in the middle. (no

Water)

Phospholipid bilayerPhospholipid bilayer

The plasma membrane is a bilayer of

phospholipids with proteins on the surface. The scattered proteins form a mosaic pattern.

The membrane is fluid because the

molecules can float side to side within the membrane.

Interactive Educational Animations

10. Cholesterol is found in the plasma membranes (highest in animal cells). It is a steroid. The human body produces 85% of the cholesterol its cells need.

Cholesterol

Cholesterol helps stabilize phospholipids because it prevents the chains of the fatty acid

in the phospholipids from sticking together.

Selectively Permeable

•The property of the membrane that allows some materials to pass through while keeping others out.