Notes on Chapter 12

Use these notes as you read the text. These will not be collected, but as you write answers to these questions you will increase your comprehension, and you will be able to better articulate what you don't understand. Comments and suggestions are most welcome!

For pages 389-395, An introduction to membranes and their lipids.

Words that you should be able to define:

Micelle

Liposome

Bilayer

Important concepts:

Behavior of lipids in aqueous environments

What is the major driving force for the formation of micelles, liposomes and bilayers?

Transition temperature

Look at table 12-2, what generalizations can you make about fatty acid composition and the temperature that was used to culture E. coli?

Role of cholesterol in lipid fluidity

How does it increase fluidity?

How does it decrease fluidity?

Movement of lipids

What is the difference between lateral diffusion of a phospholipid and transbilayer diffusion? What is required for transbilayer diffusion?

For pages 395-407, Proteins in membranes and membrane fusion.

Words that you should be able to define:

Integral

Peripheral

Annexins

Hydropathy index

Fusion proteins

Integrins (CD18 is the beta subunit of an integrin, defects in this subunit cause leukocyte adhesion deficiency, page 404)

Type I, II, III, IV, V and VI integral proteins (Figure 12-14)

Important Concepts

How did the fusion of mouse cells with human cells show that proteins are able to laterally diffuse? (Look at figure 12-7). How were the proteins visualized?

The experiment on page 397, figure 12-9 will be discussed in class.

What is the difference between EA and IEA? Why does one label proteins that are inside the cell and the other only labels proteins on the outside of the cell? How are the labeled proteins detected? What other techniques are used to determine the location of a membrane bound protein?

What type of linkages/interactions hold proteins on membranes?

Secondary structure

What is the most common structural motif in membrane spanning proteins? What is the second most common? Can the hydropathy index be used to predict this second type of structure?

Membrane fusion

Give four examples.

What is required for membrane fusion? For the two specific examples that are given, invasion of HIV and invasion of influenza, look at the figures first (skip page 406 until after you have worked through the figures.) Why does the HIV virus only invade T lymphocytes and phagocytes? (This was one of the most interesting parts of this chapter.)

Pages 408-414 Transport across membranes I: Passive Transport, no energy required

Words that you should be able to define:

simple diffusion

selectively permeable

facilitated diffusion

membrane potential (either chemical or electrical)\

osmosis (revisit chapter 4, pages 92-93)

transporters

permeases

aquaporins

Important concepts: (This section will be presented in class.)

Why are the structures of most transporters not known?

What contributes to the thermodynamic barriers that impede membrane transport?

What driving forces allow passive diffusion to occur with transporters? (Clue: pages 92-93)

How are transporters analogous to enzymes?

How do tranporters differ from enzymes?

Give examples of locations of aquaporins?

How do they work? How is their proposed structure related to their function?

Where is the GluT1 glucose transporter found? How is the proposed structure of this transporter related to its function? How is it specific for glucose?

Michalis-Menton kinetics can be applied to transporters!

What is the value of K_t for D-glucose? For galactose? For L-glucose? What does K_t mean?

Comparison of Erythrocytes and Hepatocytes

The liver has GluT2 transporters and they have a K_t value of 66 mM. If blood glucose levels were 5 mM, which tissue would take up glucose? Make a graph of velocity of glucose uptake vs glucose concentration. Aren't you impatient to learn about the glucose transporters in muscle and adipocytes?? See box 12-2!

One last type of energy free (passive) transporters: Cotransport systems.

Look at figure 12-28 to see how the chloride-bicarbonate exchanger works to shuttle CO₂ out of the tissues, into the blood as bicarbonate and then out of the lungs.

Pages 415-431 Membrane Transport II: Active diffusion (Energy required!)