Q: What are the 3 major membrane lipids? A: Phospholipids, glycolipids and cholesterol Q: Phospholipids can be derived from which 2 alcohols? A: Glycerol or Sphingosine (a more complex alcohol) Q: What does a phosphoglyceride consist of? A: Glycerol backbone, two fatty acid chains, and a phosphorylated alcohol and a sugar Q: What are the most common fatty acid chains in phospholipids and glycolipids? A: 16- and 18- carbon chains Q: How are fatty acid chains attached to glycerol? A: They form esters with the hydroxyl groups at the C-1 and C-2 positions of glycerol Q: What happens to the C-3 hydroxyl group in phospholipids and what is the by-product? A: C-3 hydroxyl is esterified to phosphoric acid & the by-product is phosphitidate (a small amount remains in membranes) Q: What happens to phosphitidate in membranes? A: The phosphate group becomes esterified to the hydroxyl group of one of the following acids: serine, ethanolamine, choline, glycerol or inositol. Forming PS, PE, PC, PG or PI. Q: What usually covers the outer leaflet of eukaryotic plasma membranes? A: Sphingolipids Q: How was the work sphingolipid derived? A: "Sphingo" is Greek for "to strangle" and it refers to the "strangling" of axon by myelin Q: What are the three major components of spingolipids? A: 1)sphingoid backbone that is amide-bound to a 2)saturated fatty acid forming ceramide and 3)a polar head group Q: What are the potential sphingolipid head groups in higher eukaryotic cells and what are they called when bound? A: glucose (glucosylceramide), galactose (galactosylceramide) and phosphocholine (sphingomyelin) Q: What is a plasmalogen? A: Phospholipid with an a,ß-unsaturated ether-linked alcohol at the C-1 of glycerol Q: What enzyme cleaves the C-2 fatty acid off of Phosphytidyl Choline (PC)? A: Phospholipase 2A Q: What is PC called if it is lacking the 2-C fatty acid? A: Lyso-PC Q: Are phospholipid head groups usually arranged symmetrically in plasma membranes? A: No, depending on the head group they usually have a preferred orientation ie. poimting into or out of the cell. Q: What are sugar-containing lipids called? A: Glycolipids Q: In animal cells what are glycolipids derived from? A: Sphingosine backbone with one or more sugars attached (primariely to the hydroxyl group) Q: What is the simplest glycolipid? A: Cerebroside, containing a single sugar residue Q: What compose ABO blood group antigens? A: Glycospingolipids Q: How many sugar residues can glycolipids have? A: Complex glycolipids (ie. ganliosides) can contain branched chains with up to 7 sugar residues. Q: Describe a ganglioside: A: Gangliosides are cabohydrate-rich sphingolipids with an oligosaccharide chain containing at least one ACIDIC sugar attached to ceramide Q: Where are the highest concentration of gangliosides found? A: In the nervous system, especially the gray matter, where the constitute ~6% of the gray matter Q: Where are gangliosides degraded? A: In lysosomes Q: What is the result of mutations that cause the inability to remove specific sugars from glycolipids? A: A variety of lysosomal storage diseases Q: How are glyceryl ether phospholipids synthesized? A: Start with dihydroxyacetone phosphate, acylation by a fatty CoA yields a 1-acyl derivative which exchanges for a long change alcohol to forman ether at C-1 Q: What kind of molecule is platlet-activating factor (PAF)? A: An ether phospholipid (1-alkyl-2-acetyl ether analogue of PC) Q: What does platlet -activating factor do? A: Subnanomolar concentrations induce agregation of platlets and dilation of blood vessels Q: What allows platlet-activating factor to diffuse between cells or into serum A: The presence of an acetyl group rather than a long-chain acyl group at C-2 Q: Is cholesterol important in membranes? A: Yes, plasma membranes of eukaryotic cells are usually rich in cholesterol Q: Phosphatidate (diacylglycerol 3-phosphate) is a common intermediate in what two pathways? A: the synthesis of phosphoglycerols and triacylglycerides Q: Name the 2 possible ways for synthesizing glycerol 3-phosphate used in the sythesis of phosphatidate (diacylglycerol 3-phosphate). A: It is mainly formed fromv the reduction of dihydroxyacetone phosphate, but a small amount is formed from phosphorylating glycerol Q: How is phosphatidate (diacylglycerol 3-phosphate) synthesized from glycerol 3-phosphate (G3P)? A: G3P is acylated by fatty acid CoA to lysophosphatidate which is acylated by fatty acid CoA to form phosphatidate Q: In most phosphatidates is are the fatty acids saturated or unsaturated? A: Usually fatty acids attached to C-1 are saturated, while fatty acids attached to C-2 are unsaturated Q: CDP-diacylglycerol is the activated indermediate in the synthesis of what? A: Some phosphoglycerides Q: How is CDP-diacylglycerol formed? A: Phosphatidate attaches to CTP and the combined moiety (ding) reacts with the hydrozyl group of an alcohol (eg. ethanolamin, serine or inositol) Q: In phosphoglyceride synthesis does CTP activate the lipid or the alcohol? A: It can activate either Q: Phosphatidyl serine can form what other 2 phosphidyl's? A: Phosphatidyl ethanolamine and phosphatidyl choline Q: Where does the choline in phosphatidyl choline come from in mammals? A: From the diet Q: How is phosphatidyl choline formed? A: Choline is phosphorylated by ATP to phosphorylcholine which reacts with CTP to form CDP-choline, then the phosphocholine is transferred to DAG to form phosphatidyl choline (ethanolamine is formed using analogous pathways just substituting ethanolamine for choline) Q: What is used to form plasmogens and other ether phospholipids? A: Dihydroxyacetone phosphate (DHAP) Q: What is the first committed step sphingolipid biosynthesis? A: Synthesis of the sphingoid backbone (condensation of palmitoyl-CoA (palmitate) and serine to form 3-ketodihydrosphingosine) Q: Where does sphingoid backbone formation take place in higher eukayotic organisms? A: On the cytosolic surface of the ER Q: Subsequent to long chain synthesis of sphingo lipids 3-ketodihydosphingosine is reduced to dihydrosphingosine, which has what characteristic bond? A: It has a trans-double bond between C-4 and C-5. Q: The N-actylation of a sphingoid backbone with saturated fatty acid forms what? A: Ceramide Q: Where do head group substituents attach to ceramide? A: C-1 Q: How many sphingolipid species do mammals make and how do they differ? A: Mammals make hundreds and they differ in precise head group modification Q: What is the most prevalent sphingolipid and what is its head group? A: Spingomyelin (18 C) which has a choline head group (transferred on by PC) Q: What is the Yin Yang relationship of sphingomyelin synthesis A: Ceramide (a pro-apoptotic molecule) reacts with PC to form sphingomyelin and DAG (a pro-growth molecule) Q: What is the most potent lipid signaling molecule currently known? A: Platlet activating factor (PAF) Q: What are the effects of platlet activating factor (PAF) A: 1. Activates platlets, neutrophils and monocytes 2. Binds GPCR's which leads to protein kinase C activation in WBC 3. Causes WBC's to adhere and migrate through epithelium Q: What inactivates platlet activating factor (PAF) A: PAF acetylhydrolase (lyso-PAF) Q: Biological membranes are composed of which two lipids A: Phospholipids and glycolipids Q: Membrane proteins are not rigid, they can diffuse a distance of ___ in one minute A: Several microns Q: What two characteristics of lipid bi-layers can make a membrane more fluid A: Short FA chains and cis double bonds Q: What is the phospholipid/choleterol ratio in eukaryotic membranes A: 1:1 Q: Cholesterol makes a lipid bilayer more rigid (less fluid), at the same time it prevents the hydrocarbon chains from doing what A: Crystallizing Q: Describe the asymmetrical distribution of phosholipdis in a bilayer A: PS, PI, PE face the cytoplasm; PC and sphingomyelin face the outer surface Q: Flipases, Flopases and scrambleases are what type of transporters A: Flip and Flop ATP dependent; scramble is ATP independent Q: How can you remember which direction flipase and flopase work A: flIp goes In: flOp goes Out Q: Name some functions of ABC transporters A: transport of lipids, bile salts, toxic compounds and peptides for antigen presentation Q: What are the two classes of resistance of anticancer drugs A: Those that impair delivery and arise in the cancer cell itself Q: What is the basis of multi drug resistance A: After a cell requires resistance to a drug it can develop resistance to strucurally and mechanically unrelated drugs, this results from expression of ATP-dependent efflux pumps with broad drug specificity Q: There is a infrequent mechanism of multi drug resistance, what is it A: activation of DNA repair or cytochrome p450 Q: Name 6 alterations in cell phys. that lead to cancer A: 1. self-sufficency in growth signals 2. insensitivity to growth-inhibition signals 3. evasion of apoptosis 4. limitless replcation potential 5. sustiaoned angiogenesis 6. tissue evasion and metastasis Q: The apoptotic program is generally present in which cells A: All of them dog Q: How long does apoptosis take and what happens to the cellular "debri" A: 30-120 minutes; the debris is taken up by nearby cells Q: What are the ultimate molecular "executioners" of the cell and what type of protein are they A: Caspases which are cysteine proteases Q: What type of lipids are most affected in tumor cells? A: Glycolipids and phosphlipids, whith ether-linked lipids found abundantly in metastatic variants. Q: Are lipids uniformly distributed within biological membranes? A: No, biological membranes contain a variable number of lipid rafts, making them non-uniform. Q: What is a lipid raft? A: Membrane microdomains enriched in cholesterol and glycosphingolipids, but deficient in glycerol phospholipids. Q: What are likely functions of rafts and caveolae? A: Probably involved in signal transduction, endocytosis, and cholesterol trafficking. Q: What is a caveolae? A: Small, flask shaped invaginations found as single entities or grape-like clusters. Q: What type of proteins are found in caveolae? A? Caveolin-1, GPI-linked proteins, and numerous cell signaling proteins. Q: What is a clathrin coated vesicle? A: Large protein complexes that form vasket like lattices on the inner surface of plasma membranes. Q: What is the function of clathrin coated vesicles? A: Mediate sorting/selective transport of membrane bound proteins between the trans Golgi and the plasma membrane. Q: What is the sequence in the formation of CCV's? A: Phosphatidylinositol 4,5 PO4 recruits adapter proteins which recruit clathrin. Q: How does cholera toxin enter a cell? A: Bind glycolipids that associate with lipid rafts at cell surface. Carried retrograde to the golgi and ER. Partially unfolds so that it is targeted to the proteasome, but upon entering cytosol refolds and avoids destruction. Q: What lipids can be added to proteins co- or post-translationally that target them for insertion into the cell membrane? A: Myristate, palmitate, farnesyl, geranylgeranyl, and Glycosylphosphatidylinositol GPI. Q: What processes target G-protein coupled receptors for insertion in the cell membrane? A: Covalent attachment of palmitate or prenylation near the COOH-terminus. Q: What is Ras? A: A signal transducing G-protein that plays central roles in the control of cell growth. Q: How is Ras activated? A: Ligand stimulated activation of the cell surface receptor associated tyrosine kinase activates Ras. Q: How does Ras function? A: Activated Ras stimulates a cascade of serine/threonine kinases to initiate transcriptional activations of genes. Q: How is Ras post-translationally modified? A: By prenylation, a process that involves the addition of a 15-carbon farnesyl isoprenoid moiety. Q: What is thought to be the purpose of Ras prenylation? A: Thought to facilitate membrane targeting. Essential for Ras function. Q: What treatment is available for cancers involving mutant Ras function? A: Inhibitors of the enzyme that catalyzes Ras farnesylation. Q: What is the fate of proteins attached to the lipid glycosylphosphatidylinositol? A: Proteins with the attached phospholipid, associated sugars, and ethanolamine are destined for the cell surface. Q: Prion diseases may present as genetic, infectious, or sporadic disorders, all of which involve modification of what protein? A: The prion protein (PrP) Q: Give one example of a prion disease in cows, in sheep, and in humans. A: Bovine spongiform encephalopy (Mad Cow Disease is a type of BSE), scrapie of sheep, and CJD of humans. Q: Prions are composed exclusively of what? A: Modified PrP called PrPSc (Sc superscripted), which is devoid of nucleic acid. Q: What secondary protein structure is found in abundance in PrPSc but not in PrPC (normal)? A: Beta sheets. Q: How does PrPSc affect PrPC to cause disease? A: Transgenic studies argue that PrPSc acts as a template upon which PrPC is refolded into a new PrPSc molecule through a process facilitated by another (unknown?) protein. Q: What mechanism/action can prevent formation of PrPSc? A: Redirecting the cellular isoform of prion protein (PrPC) to clathrin-coated pits (vs. causitive targeting of PrPSc to calveolae-like domains by GPI anchors). Q: Efficient formation of the scrapie isoform (PrPSc) of prion protein requires targeting of PrPSc to where by what anchors? A: GPI anchors (to which the PrP protein precursor becomes attached, see p.25 of slides) targets PrPSc to calveolae-like domains of the plasma membrane.