1. CHAPTER 4 A VIEW OF THE CELL
I. Two basic cell types
A. Prokaryotes
1. Cells lacking internal , membrane-bound
structures
2. Mostly unicellular organisms
a. Composed of only one cell
B. Eukaryotes
1. Cells containing internal, membrane-bound
structures
2. Mostly multicellular organisms
a. Composed of more than one cell
3. Organelles
a. The membrane-bound structures w/in
eukaryotic cells

2. 4.5 The structure of membranes correlates with their function
I. Maintaining a balance
A. All cells must maintain a balance regardless of internal and external conditions
1. Homeostasis
B. How does the plasma membrane maintain homeostasis?
1. Selective permeability
a. Allowing some molecules into the cell while keeping others out
b. Think of it like the screen in your window
1. Fresh air comes in while bugs are kept out
II. Structure of the plasma membrane
A. Basic building block
1. Phospholipid
a. A lipid molecule that has a phosphate molecule attached to it
1. The phosphate
a. Makes the head of the molecule
b. Phosphates are polar/Hydrophilic
1. attracted to water

3. 2. The lipid
a. Makes the tail of the molecule
b. Lipids are nonpolar/Hydrophobic
1. Moves away from water
B. Phospholipid bilayer
1. Cells are surrounded by water
a. The phosphate allows the plasma membrane to interact with its watery env.
1. But it takes 2 layers of phospholipids
a. Why?
2. The 2 layers of phospholipids make a sandwich
a. The lipids form the interior of the membrane
b. The phosphates form the exterior of the membrane
c. A barrier is created that is hydrophilic on the outer surface and hydrophobic in the middle

4. 3. The bilayer is fluid
a. The phospholipid bilayer is not a rigid structure
1. The phospholipid molecules are able to move around w/in the plasma membrane
a. This allows the cell to be flexible
C. Membrane proteins
1. So how do things get into and out of the cell that cannot pass through the cell membrane?
a. Proteins molecules
2. 3 types of plasma proteins
a. Transport proteins
1. Channels or passageways through membrane
2. Think of them like locked doors
a. only molecules with a key can enter
b. each channel will only admit certain molecules

5. b. Receptor proteins
1. Conveys info from the external env. to the internal env. and visa versa
c. Marker proteins
1. Identifies cells as being one of yours
2. If a cell does not have this marker it will be destroyed