Cell Membrane

What cells have a cell membrane…• ALL cells have a cell membrane!– Prokaryotic and Eukaryotic

Cell Membrane’s Job…• Forms a boundary between a cell and the

outside environment• Controls the passage of materials into and out

of a cell

What is the cell membrane made of?

• A double layer of phospholipids–Hydrophilic Heads-”water loving”-are

exposed to water inside and outside the cell–Hydrophobic Tails-”water fearing”-

cannot be exposed to water

Phospholipid

The cell membrane also has…

• Molecules embedded within the phospholipid layers– Cholesterol molecules-provide strength for

membrane– Proteins-help materials cross the membrane– Carbohydrates-attach to membrane proteins and

serve as identification tags

Cell Membrane Structurecell membrane carbohydrate

chain

protein

protein channelcholesterolprotein

Fluid Mosaic Model

• Describes the arrangement of the molecules that make up the cell membrane

• Cell membrane is flexible, not rigid.• The phospholipids in each layer can move

from side to side and slide past each other.

http://youtu.be/Rl5EmUQdkuI

Property of the Cell Membrane

• Selective Permeability (semipermeable)–Cell membrane allows some, but not

all, materials to cross into or out of the cell.–Enables cell to maintain homeostasis

Concentration-number of particles present in a solution

Which side, outside or inside, has the highest/lowest concentration?

How do molecules move across the cell membrane?

• Several different ways molecules will move.– Some ways require the cell to use energy and

some do not.• How a molecule moves across the membrane

depends on:– Size – Polarity– Concentration inside the cell vs. outside the cell

Examples of materials moving across the cell membrane…

• Small nonpolar molecules move easily across the membrane

• Small polar molecules are transported via proteins

• Large molecules are moved in vesicles