2 Membranes

50%

the plasma membrane accounts for 10% of the cell volume

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)

• • 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

• 1. Phospholipids
• 2. Sphingolipids
• 3. Cholesterol
• 4. Eicosanoids

ASYMETRICALLY

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

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

induces uterine contractions (PGE₂), carries out vasodilatation, platelet aggregation, vasoconstriction

induce platelet aggregation (TXA₂) & vasoconstriction

• 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

• 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)

1. Polar head groups (Choline)

2. Phosphate group

3. Glycerol group

• 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

HIV

Measles [cells infected with measles can fuse with healthy cells resulting in the spread of the virus]

they are structurally similar & perform similar functions in the plasma membrane, but sphingolipids DO NOT have fusogenic properties

• 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

different types of lysosomal storage diseases result

• each caused by a single enzyme defect

• to “fix” can either replace enzyme or break down whatever protein is being built up

caused by a deficiency in Hexosaminidase A that disrupts sphingolipid breakdown resulting in buildup of GM2 ganglioside

causes mental retardation, blindness & early death

caused by a deficiency in Glucocerebrosidase

Glucocerebroside builds up

causes hepatosplenomegaly, mental retardation & long bone degeneration

can be treated with enzyme replacement therapy

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

sphingomyelinase deficiency

sphingomyelin builds up

results in mental retardation, hepatosplenomegaly

GM1 Gangliosidase deficiency

GM1 ganglioside builds up

results in mental retardation, bone malformations, hepatomegaly

• 1. Double Bonds
• 2. Acyl Chain Length
• 3. Temperature
• 4. Cholesterol

• More double bonds: increased fluidity (kinkier)

• Fewer: decreased fluidity (more rigid)

• Shorter: MORE fluid

• Longer: less fluid

• higher temp: more fluid

• lower temp: less fluid

• 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)

AT BODY TEMPERATURE

• 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!)

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

1. signal transduction

2. endocytosis

3. rapid re-organization of the membrane for extracellular matrix modification & motility

~20-25

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

• • 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

• 1. blood-type antigens
• 2. pathogen recognition sites
• 3. reservoir for cytokines/growth factors

• • 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

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