Membranes: Structure and Function 9/23

1. Membranes: Structure and Function 9/23 Significance of phospholipid bilayer protein content. Membrane permeability characteristics. Membrane lipid moieties and their significance. Blood typing and membrane lipids/carbohydrates. Membrane lipids as source of second messengers. Transmembrane hydrophathy plots of R-group function.

2. Term Paper Topics that become a title Do you have a specific topic related you want to be professionally? Example: Why does expression of high expression of chemokine receptor 4 result in osteosarcoma? Do you have some obscure disease and need to find out more about it? Example: What does my liver dysfunction cause early hypercholesterolemia and stroke? Did you read about something and just want to learn more because it is really cool? Example: What happens to Creatine Phosphate DeltaG in bear brain cells during hibernation? Did you receive a medical treatment and wonder how it worked? Example: How does cortisone treatment alter fibroblast transcription/translation during carpal tunnel syndrome treatment? Narrow topic as much as possible, but stil lbe sure it comes up with 20-50 hits in PubMed or Agricola….narrow focus = easier paper writing We will narrow this to a tentative title later…..

3. Most folks find it quite surprising to learn that sometimes a lipid bilayer can actually contain more “protein” that phospholipids and cholesterol. What are the functions of these proteins and why is it that something like an inner mitochondrial membrane NEEDS such a high protein content?

4. Permeability is a function of solute and membrane characteristics! How would these solute characteristics alter permeability of the solute? • Solute Size • Solute Charge • Solute Gradient • Environmental Temperature

5. How would these membrane characteristics alter permeability? FA -CH=CH- bonds: 2) FA chain length: 3) Presence of Cholesterol: 4) PL Density:

6. Cholesterol can decrease membrane permeability to H2O and Na+ by filling pockets (cavities) created by cis -CH=CH- bonds in PL fatty acid chains, and INCREASE the fluidity of the middle of the plasma membrane. Paradoxically it can also DECREASE membrane fluidity because the rings structure has less “flex” than a single hydrocarbon chain of a FA..

7. Carbohydrate “moieties” can also attach to the lipids of the PL bilayer: Glycolipids (via sphingosine without Pi) and GPI (glycophosphatidyl inositol) Sphingosine is base for carbohydrates and FA Tail

8. ABO Blood typing: how do you know what erythrocytes are yours and which should be destroyed? Larger slightly different polysaccharide moieties determine erythrocyte half life.

9. Why do we take “Ibuprophen” at the level of a plasma membrane?Some cells cleave specific lipids and use PL to generate hormones and other extra/intracellular signals. The formation of arachidonic acid (a committed step) is a classic for inflammation!

10. Proteins often have carbohydrates attached for use in: 1) Cell-cell recognition, 2) Receptor sites, and 3) Protection! This is VERY important physiologically and pathologically. There are two types of carbohydrate-protein linkage: O-linked or N-linked • N-asparagineO-usually Serine or Threonine • Polysaccharides linked by glycosidic bonds!(R-O-R) • Saccharides can form single or branched chains! Classic Functions: • Function in major histocompatability complexes: • Role related to cancer treatment: • Function of glycocalyx lining gut and endothelium: • Function for bacteria causing urinary tract infections : • Function for parasitic infection

11. How are carbohydrates attached to trans-, intergral or peripherally located proteins?Glycoproteins typically use either O- or N-linkages with either Straight or Branched Sugar Chains

12. Why are glycoproteins important if you are HIV positive? • Structure of HIV gp120 envelope glycoprotein in complex with the CD4 receptor and a neutralizing antibody • http://people.ucsc.edu/~bbaatar/

13. FIGURE 15 Freeze-fracture micrograph showing an RBC ghost membrane (G) adherent to a WGA-coated schistosomulum (S) after 3 h of incubation. The protoplasmic faces of the tegumental membranes are seen with the fracture plane passing generally through the intramembrane particle-poor outer membrane (P2) and occasionally exposing the intramembrane particle-rich inner membrane (P1). No alterations are seen in the area where the ghost is attached. The fracture was performed under mild etching conditions, s, spines; p, pits. x 22,000.(Caulfield and Cianci . JCB. 1985; 101: 158.

14. How do we IDENTIFY the classes of protein one finds associated with the plasma membrane based on their amino acid sequence? Remember that not ALL membrane proteins may be free to diffuse about the membrane, some may be anchored to a particular place.

15. We often study proteins by indirectly looking at the DNA they were transcribed/translated from. This is cheaper and easier than direct protein sequencing!

16. How do hydropathy analysis of a DNA sequence help us predict protein functions? Why is this useful? Human Genome Project and our proteins/diseases!

17. How do cells “limit” membrane protein mobility? • Typical cell fusion results: • Additional evidence for the Fluid Mosaic Model • Tags: fluorescent antibodies • Why must protein mobility sometimes be limited to a specific location? • Gap Junctions: • Enterokinase: • Na+/Glucose co-transporter: • Aquaporin: • Does this apply to prokaryotes? Why/WhyNot?

18. Are all the proteins associated with the PM floating freely about the PM? Certainly Not! Some proteins HAVE to be anchored in the cytosolic side to certain locations by the proteins actin, ankyrin, and spectrin!