1. I. MEMBRANE STRUCTURE AND FUNCTION
Chapter 7
I. MEMBRANE STRUCTURE AND FUNCTION
A. Membranes organize the chemical activities of cells by allowing things in and out
1. The plasma membrane exhibits selective permeability--screen
B. Phospholipids
1. Form a bilayer in water.
a. Why they are selectively permeable.
b. Nonpolar molecules
c. Polar molecules
2. Amphipathic molecule
a. the head (glycerol and phosphate) is polar
or hydrophilic.
b. the tail (the fatty acids) are nonpolar
or hydrophobic
C. Read about how Fluid mosaic model was developed (pg. 126)

2. C. The fluid mosaic model. 1. Mosaic… 2. Fluid…
a. Refers to the way the lipids and proteins behave in a membrane.
b. Molecules are not bonded together, so are free to shift.
c. Must remain "fluid" for membranes to function.
3. Some proteins are attached to the cytoskeleton and fibers in the extracellular matrix.
4. Most of the phospholipids have kinked tails…
5. Also contains cholesterol…
a. keeps the membrane from solidifying
b. keeps the membrane from being total liquid
6. Glycoproteins…protein with attached sugar on outside of
membrane.
Glycolipid…lipid with attached sugar on outside of membrane.
Fibronectin
Collagen
Integrin

3. Ways to keep membrane fluid
Hibernation animals increase cholesterol production

4. D. Proteins give the membrane function
1. Made in the rough ER
2. Functions of proteins in the membranes
a. Transport
b. Enzymatic activity
c. Signal Transduction (Receptor sites for signals)
d. Intercellular Joining
e. Cell-cell recognition
f. Attachment to cytoskeleton and extracellular matrix
3. Types of membrane proteins
a. Integral - inserted into the lipid bilayer.
b. Peripheral - not embedded in the lipid bilayer, but are attached to the membrane surface.
How do the integral proteins stick to the membrane?

5. D. Proteins give the membrane function
1. Made in the rough ER
2. Functions of proteins in the membranes
a. Transport
b. Enzymatic activity
c. Signal Transduction (Receptor sites for signals)
d. Intercellular Joining
e. Cell-cell recognition
f. Attachment to cytoskeleton and extracellular matrix
3. Types of membrane proteins
a. Integral - inserted into the lipid bilayer.
b. Peripheral - not embedded in the lipid bilayer, but are attached to the membrane surface.
How do the integral proteins stick to the membrane?
By the solubility of their amino acids.

6. Hydrophilic Amino Acids
Hydrophobic Amino Acids
Hydrophilic Amino Acids

7. 1. The lipid composition of the two layers is different.
E. Membranes are Bifacial (meaning, there is an inside and outside face)
1. The lipid composition of the two layers is different.
2. The proteins have specific orientations
3. Carbohydrates are found only on the outer surface
a. Branched oligosaccharides form glycolipids and glycoproteins on external surface.
b. Function - recognition of "self" vs "other”.
Question: On which side of a vesicle membrane are the carbohydrates?

8. Question: How do materials get across a membrane
Answer:
First, there are two problems.
1. The lipid bilayer is hydrophobic. Hydrophilic materials don’t cross easily.
2. Large molecules don’t cross easily. Too big to get through membrane.
So…. There are two mechanisms
1. Passive transport (diffusion, osmosis, facilitated diffusion)
2. Active transport (carrier mediated, endocytosis, exocytosis)

9. F. Transport proteins
1. Hydrophilic substances can avoid contact with the lipid bilayer by passing through these proteins.
2. “Channel Proteins”
a. Aquaporins
3. “Carrier Proteins”
4. These proteins are specific in what they transport.
a. glucose carrier protein is so specific that fructose can’t even flow through.
5. What determines the direction substances flow?

10. G. Diffusion: passive transport across a membrane
1. Definition
a. lungs
b. water
2. Passive transport
3. Concentration gradient…
a. 2 or more substances move independently of each other.
b. Solute/Solvent
c. Concentration
4. Equilibrium

12. 5. Factors that Effect Diffusion
a. Concentration
b. Temperature
c. Particle size
d. Mixing

13. H. Osmosis: passive transport of water
1. Definition
2. Tonicity: the ability of a solution to cause a cell to gain or lose water
a. Hypertonic
b. Hypotonic
c. Isotonic

14. GFP labeled Aquaporins
a. newly found channels for osmosis
GFP labeled Aquaporins

15. I. Osmoregulation
1. Definition
2. Animal cell versus Plant cell (why different?)
a. Flaccid
b. Turgid
c. shriveled and death

16. J. Facilitated Diffusion (carrier proteins and channel proteins)
1. Two types of channel proteins
a. open hydrophilic channels
b. gated channels (ion channels)
2. If protein not present…
3. Passive transport
4. Rate of diffusion

17. Facilitated Diffusion

18. 2. Against the concentration gradient.
K. Active Transport
1. Definition
2. Against the concentration gradient.
3. Steps: (see picture)
4. Examples:
a. Na+- K+ pump
b. Electrogenic or H pumps (CR & Ps)
c. Cotransport Movement of H+ that allows other materials to be transported into the cell as the H+ diffuses back across the cell membrane.
Example - Sucrose transport

20. Active Transport
Sodium Potassium Pump

21. Cotransport
A “pump” that is powered by ATP builds up a concentration gradient that is then used by another carrier protein to transport something else. The energy for the second transport is from the flow of the first substance down its concentration gradient.

22. L. Exocytosis and Endocytosis
1. Exo means outside
2. Kytos means cell
3. Exocytosis
4. Endo means inside
5. Endocytosis
Three types:
a. Phagocytosis
b. Pinocytosis
c. Receptor-mediated endocytosis

23. Exocytosis
Endocytosis

24. M. Bad membranes can cause more cholesterol to be in blood.
1. Our liver removes excess cholesterol from our blood.
a. receptor-mediated endocytosis
2. People with high cholesterol either do not have receptors or have low amounts of protein receptors on the membrane of liver cells.

25. Making Connections