Chapter 7.2

I. The Plasma Membrane Surrounds the
Cell.
 Boundary between the cell and its watery environment.
 the cell (ex: nutrients
Plasma and waste).
 Function: maintain homeostasis (balance) for the cell.

The Plasma Membrane is a selectively permeable membrane.
 Allows some molecules to enter and keeps others out
 Selective barrier (like a screen door, coffee filter)

 Composed of two layers of phospholipids, called the “phospholipid bilayer”.
Phospholipid molecule
Polar head
(includes phosphate group)
 Phospholipids are lipids with a phosphate attached to them.
Nonpolar tails
(fatty acids)

 The phosphate head is polar
(hydrophilic = loves water), so it interacts with the watery environment inside the cell and outside the cell.
 The fatty acid tails are nonpolar
(hydrophobic = afraid of water) so they avoid water.
Polar heads love water
Non-polar tails hide from water


Fluid because it moves like water http://www.stolaf.edu/people/gi annini/flashanimat/lipids/mem brane fluidity.swf
 Mosaic because the proteins make a pattern on the surface.
Carbohydrate chains
Proteins
Transport
Protein
Phospholipids

III. Other parts of the Plasma Membrane
1. Cholesterol – stabilizes the phospholipids and prevents the fatty acid tails from sticking together.

2.
Transport proteins – move needed substances and waste through the plasma membrane, they regulate which molecules enter and leave.

3.
4.
Inner surface proteins – give cell its flexibility
Carbohydrate chains – stick out from the surface of plasma membrane, identifies chemical signals and other cells.
Proteins
Carbohydrate chains
Transport
Protein
Phospholipids