1. Section 2 The Plasma Membrane
Chapter 7
Section 2
The Plasma Membrane

2. Plasma Membrane Remember from section 1 notes:
All cells have a plasma membrane
Both Eukaryotic & Prokaryotic

3. What is the plasma membrane?
A thin, flexible boundary between ALL cells and their environment that controls what can and cannot ENTER and EXIT
Maintains HOMEOSTASIS - the balance in the cell’s internal environment

4. Selective Permeability
The property of the plasma membrane that ALLOWS/PERMITS some substances to pass through while PREVENTING the passage of others
The control of how, when, and how much of these substances enter and leave a cell relies on the STRUCTURE of the plasma membrane

5. Selective Permeability
The plasma membrane is composed of a PHOSPHOLIPID bilayer, in which TWO layers of phospholipids are arranged tail-to-tail (which allows it to exist in a watery environment)
Each phospholipid consists of a “head” with TWO “tails”
The “head” is a PHOSPHATE which is polar – and is therefore ATTRACTED to water
The “tails” are FATTY ACID, which are nonpolar – and are therefore REPELLED by water

6. Selective Permeability
The fatty acid “tails” form the INTERIOR of the plasma membrane
The phosphate “heads” face the INSIDE and OUTSIDE of the cell

7. Selective Permeability
This arrangement allows the polar heads to be closest to the WATERY environments found inside and outside the cell and the nonpolar “tails” to be AWAY from the water
Therefore, water-soluble substances CANNOT move easily through the plasma membrane

8. Fluid Mosaic Model
A pattern created on the surface of the plasma membrane by PROTEINS, CARBOHYDRATES, and CHOLESTEROL moving with and among the phospholipids