2 Membranes

  1. What percent of the total cell volume can be attributed to MEMBRANES?

    the plasma membrane accounts for 10% of the cell volume

    Image Upload 1
  2. Membrane Chemical Composition: Take-home Message
    most membranes are a little less than half protein, a little less than half lipid, & have a small amount of carbohydrate (this can vary greatly depending on the function of the membrane)
  3. Notable Membrane Compositions
    • • Myelin: 79% lipid, 18% protein, 3% carbohydrate
    • - proteins are amphoteric (can conduct electricity) but lipids can’t; good way to protect electrical impulses from going astray

    • • Mitochondrial Inner Membrane: 76% protein, 24% lipid, <1% carbohydrate
    • - ox.phos enzymes & ion exchange proteins are necessary for ox.phos to occur
  4. List the classes of membrane lipids in order of abundance in most membranes:
    • 1. Phospholipids
    • 2. Sphingolipids
    • 3. Cholesterol
    • 4. Eicosanoids
  5. How are lipids distributed in the membrane?

    this is important because the outer leaflet is generally much more fluid than the inner leaflet, allowing lipid rafts to rapidly concentrate ligand-receptor pairs at specific sites on the membrane for internalization
  6. Eicosanoids
    made from the phospholipids in the plasma & make up a small, but important part of the plasma membrane; are precursors for major regulatory functions within the cell

    3 classes = Prostaglandins, Leukotrienes, Thromboxanes
  7. Prostaglandins
    induces uterine contractions (PGE2), carries out vasodilatation, platelet aggregation, vasoconstriction
  8. Thromboxanes
    induce platelet aggregation (TXA2) & vasoconstriction
  9. Leukotrienes
    • induce vasodilation & bronchoconstriction in asthma (LTC4, LTD4, LTE4) & are components of SRS-A [slow reacting substance of anaphylaxis, discovered in individuals suffering from anaphylaxis]
    • • create problem of suffocation during anaphylaxis & an asthma attack
  10. Phospholipids
    • provide the major structure for the plasma membrane

    • have hydrophilic head + fatty acids that make up the hydrophilic interior of the PM (usually 16-18 Cs long)

    • are capable of FUSING (energetically favorable process)

    Image Upload 2
  11. What are the components of the phospholipid head?
    1. Polar head groups (Choline)

    2. Phosphate group

    3. Glycerol group
  12. HIV & the Fusogenic Property of Phospholipids
    • lipid membranes can rapidly & spontaneously fuse with one another (eg. lipid vesicles can fuse with membrane-bound organelles or with the PM)

    • HIV has a viral coat protein that’s recognized by CD4 receptor on T-cells, macrophages, & other cell types

    • when CD4 positive cells bind HIV, a rapid fusion of the viral coat lipids with the host cell membrane occurs

    • this results in entry of the viral capsid & nucleoproteins into the host cell cytoplasm where replication of the viral genome ensues

    • viral glycoprotein recognized by CD4 is inserted into the infected cell PM

    • this infected cell can now fuse with other CD4 positive cells, even in the absence of external virus

    • resulting multi-nucleated syncytium is incapable of rendering a proper immune response
  13. What two viruses utilize the fusogenic properties of phospholipids (aka cell membranes) to spread?

    Measles [cells infected with measles can fuse with healthy cells resulting in the spread of the virus]
  14. What’s the do sphingolipids & phospholipids have in common & how do they differ?
    they are structurally similar & perform similar functions in the plasma membrane, but sphingolipids DO NOT have fusogenic properties
  15. Sphingolipids
    • made up of 2 straight chained FAs; they have no (cis) double bonds, are fully saturated

    • also have different head groups than phospholipids

    • 2nd most numerous type of membrane lipid in the PM after phospholipids
  16. What happens if the cell does not dispose of sphingolipids properly?
    different types of lysosomal storage diseases result
  17. Diseases of Sphingolipid Metabolism
    Image Upload 3

    • each caused by a single enzyme defect

    • to “fix” can either replace enzyme or break down whatever protein is being built up
  18. Tay-Sachs Disease
    caused by a deficiency in Hexosaminidase A that disrupts sphingolipid breakdown resulting in buildup of GM2 ganglioside

    causes mental retardation, blindness & early death
  19. Gaucher’s Disease
    caused by a deficiency in Glucocerebrosidase

    Glucocerebroside builds up

    causes hepatosplenomegaly, mental retardation & long bone degeneration

    can be treated with enzyme replacement therapy
  20. Fabry’s Disease
    α-Galactosidase A deficiency results in ceramide build up in lysosomes

    characteristics include a skin rash & kidney failure

    can be treated with enzyme replacement therapy
  21. Niemann-Pick Disease
    sphingomyelinase deficiency

    sphingomyelin builds up

    results in mental retardation, hepatosplenomegaly
  22. GM1 Gangliosidosis
    GM1 Gangliosidase deficiency

    GM1 ganglioside builds up

    results in mental retardation, bone malformations, hepatomegaly
  23. Factors Affecting Membrane Fluidity
    • 1. Double Bonds
    • 2. Acyl Chain Length
    • 3. Temperature
    • 4. Cholesterol
  24. Double Bonds effect on Fluidity
    • More double bonds: increased fluidity (kinkier)

    • Fewer: decreased fluidity (more rigid)
  25. Acyl Chain Length effect on Fluidity
    • Shorter: MORE fluid

    • Longer: less fluid
  26. Temperature effect on Fluidity
    • higher temp: more fluid

    • lower temp: less fluid
  27. *Cholesterol effect on Fluidity*
    • more cholesterol: LESS fluid

    • less cholesterol: more fluid

    just remember cholesterol has an inverse relationship with fluidity (the more C, the less fluid, the less C, the more fluid)

  28. Walking (Mycoplasma) Pneumonia
    • mycoplasma bacteria enters the lungs & attaches to the base of respiratory cilia where it extracts cholesterol from the plasma membrane surrounding the cilia

    • this causes the cilia membrane to become limp & incapable of beating, which results in mucous accumulation in the respiratory tract & provides a rich environment for mycoplasma to thrive

    • secondary bacterial pneumonia often sets in with untreated mycoplasma pneumonia, as proper cilia function is an important part of the body’s ability to combat pathogenic organisms

    • most common pneumonia in humans (+ pigs!)
  29. Lipid Rafts
    specialized cholesterol & sphingolipid-rich microenvironments in the membrane that move rapidly in a leaflet

    • are major functional organizers of the membrane, bringing lipids & proteins together
  30. What are lipid rafts critical for?
    1. signal transduction

    2. endocytosis

    3. rapid re-organization of the membrane for extracellular matrix modification & motility
  31. How many amino acids (AAs) does it take to span a membrane?

    • AAs are almost all hydrophobic in the middle membrane-spanning segment

    Image Upload 4
  32. Band 3 Protein
    • • the anion exchanger in RBCs
    • • has 14 membrane spanning sections
    • • has oligosaccharides that can help it stick to the ECM
    • • on the N-term site it has binding sites that anchor it
    • • knows when to start exchanging anions
  33. What are 3 functions of carbohydrates on the cell surface?
    • 1. blood-type antigens
    • 2. pathogen recognition sites
    • 3. reservoir for cytokines/growth factors
  34. Toxoplasmosis
    • • toxoplasma is a pathogen found in cat feces that has the potential to cause severe birth defects in unborn children
    • • protozoan binds to certain cells in the body based on the glycoproteins expressed on those cells
  35. Coccidiosis
    coccidia recognize specific carbohydrates on the intestinal epithelial cell surface

    • a major cause of very serious GI problems in countries that have issues with water/food supply
Card Set
2 Membranes
Cell Bio Exam 1