A. Functions of cell membranes

1. semipermiable barrier
2. site for chemical reactions
3. information reception
4. compartmentalization within cells

B. Fluid mosaic model - cell membranes are more fluid than solid

C. Components of cell membranes

1. phospholipid bilayer (lipids)
2. cholesterol (a lipid)
3. proteins
4. carbohydrates

D. Cholesterol affects the fluidity of cell membranes

E. Membrane proteins

1. integral
2. peripheral
3. some can move within the membrane

F. Membrane carbohydrates act as recognition sites.

1. they are hightly specific
2. one function - cells of one organism can recognize cells of another organism

G. Which molecules pass through membranes easily?

1. small hydrophobic molecules
2. water

H. Many hydrophobic substances cannot pass though cell membranes easily (many ions for example)

I. Passive transport

1. simple diffusion
2. osmosis
3. channel proteins
4. facilitated diffusion
a. carrier proteins
- uniport
- symport
- antiport
5. concentration gradient - allows passive transport to occur

J. Active transport

1. energy and carrier proteins required
2. substances are moved against their concentration gradient
3. primary - ATP is used directly
4. secondary - energy from other molecules moving down a concentration gradient is used
5. example - sodium-potassium pump

K. Endocytosis

1. phagocytosis
2. pinocytosis
3. receptor-mediated endocytosis
a. coated pits
b. clathrin

L. Exocytosis