1. 11/8/2011
Objective: Understand that the phospholipid bilayer is fluid and selectively permeable
Warm-Up: Define hydrophobic, hydrophilic, and amphipathic.

2. If you pour a bunch of amphipathic molecules into a beaker of water, how would they arrange themselves? Draw your hypothesis.

3. Cell Membranes

4. Membrane Structure The cell membrane is a phospholipid bilayer
Each phospholipid has a polar phosphate group (often called the “head”) and non-polar fatty acids (often called the “tails”)
The polar phosphate group is hydrophilic
The non-polar fatty acids are hydrophobic
The extracellular fluid and the intracellular fluid are both aqueous solutions
Define “extracellular” and “intracellular”

6. 11/11/2011
Objective: Describe the structure and function of the selectively permeable cell membrane
Warm-Up: How are organisms able to move solutes across the cell membrane against their concentration gradient?

7. Membrane Structure
Cell membranes also contain cholesterol molecules, which help stabilize the membrane
Transmembrane proteins
There are proteins that span the cell membrane, connecting the inside of the cell with the surrounding environment
These membrane proteins function as channels that allow certain molecules to pass through the membrane
There are also membrane proteins that act as receptors

10. Cell Membrane Function
Membranes act as a barrier between the internal and external environments of the cell
Membranes are fluid
Phospholipids float around within the membrane
Membranes regulate the flow of substances into and out of the cells
There are some molecules that can diffuse freely across cell membranes
Other molecules cannot diffuse across the membrane

11. Who’s Allowed In?
Generally, small, uncharged molecules can diffuse across the membrane
Oxygen, carbon dioxide
Small, uncharged, polar molecules can also diffuse freely
Water, glycerol
Large, uncharged, polar molecules cannot diffuse through the membrane
Glucose, amino acids, nulceotides
Ions cannot diffuse through the membrane
H+, Na+, K+, Ca2+, Cl-, etc

12. Selectively Permeable
Selectively permeable (sometimes called semi-permeable): describes a membrane that only allows specific kinds of substances to pass through
Think of the root word “permeate” to help you remember this one
“Large and charged”—molecules that are large and/or charged cannot diffuse freely across the selectively permeable cell membrane