BMB 462 Lecture 2 Outline of Last Lecture I. Definition of a LipidII. Structure and function of fatty acidsIII. Structure and function of triacylglycerolsOutline of Current Lecture I. Introduction to Membrane lipidsa. Basic Structureb. Basic propertiesII. Classes of Membrane lipidsa. Glycerophospholipidsb. Galactolipids/Sulfolipidsc. Sphingolipidsd. Sterolse. IsoprenoidsIII. Lipase activityIV. Lipid SignalingCurrent LectureConcepts to remembers from previous courses/lectures:- Organic chemistry structures (specifically glycerol, fatty acid, esters)- Charged groups vs. Net charge- EntropyMembrane lipids form a bilayer containing a hydrophobic interior contained by 2 hydrophilic barriers separating the hydrophobic interior of the membrane from the aqueous environment and cell/organelle interior.-The shape of a single membrane phospholipid is more cylindrical than a fatty acid; free phospholipids in solution can fold back along themselves to form a double layer liposome (as opposed to a micelle)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The bilayer forms because hydrophobic areas in water force the water molecules to make a structured cage around the molecules – water does not like structured arrangements, it prefers to be disorganized and to have higher entropy.Separating the hydrophobic side of phospholipids from water allows an increase in entropy.- To be a membrane lipid, there needs to be a polar and a nonpolar endI. Introduction to Membrane Lipidsa. Basic structure includes:i. Amphipathic – molecules that contain both hydrophobic/nonpolar and hydrophilic/polar portions1. The polar head group (can be Phosphates/phosphodiesters, sugars/hydroxyl groups, etc)2. Hydrophobic portion (fatty acid tails of Carbons and Hydrogens, Isoprene derivatives, etc)ii. Variety of combinations from diverse head groups and tails available; see Classes of Membranesiii. Backbone made of either glycerol or sphingosineb. Basic Properties: The amphipathic nature and shape of phospholipids allows the formation a lipid bilayer.i. The hydrophilic head is exposed to the aqueous environmentii. The hydrophobic tails are buriediii. Lipids in a membrane are held together via Van der Waals interactions, and similar loosely connected forces, not covalent bonding.II. Classes of Membranes:a. Glycerophospholipidsi. Contain a glycerol backboneii. Fatty acids are attached via ester bonds to Carbon 1 and Carbon 21. Carbon 1 can be bond with an ether linkage; there is a lot more diversity with this bond in plants than in mammals/prokaryotesiii. The polar head group is attached to Carbon 3 with a phosphodiester bondiv. Different fatty acids and head groups change the properties of the lipids (i.e. solubility in organics or aqueous solvents, polarity, etc)v. Carbon 1 is often saturated while Carbon 2 is typically the one with one or more double bonds (mono- or poly-unsaturated)vi. Glycerophospholipids are a major component in the membrane and can be used as a precursor for signal molecules1. Refer to chart on pg. 8 in the class notes for names and structures of different types of glycerophospholipids. Key derivatives include phosphatidylethanolamine (PE), phosphatidylcholine (PC),phosphatidylserine (PS), and Phosphatidylinosiol 4,5-bisphosphate(PI)b. Galactolipids & Sulfolipidsi. These structures are mostly found in plants1. Plants have trouble making phosphate but have the ability to make plenty of galactose. Plant cells would have a shortage of phosphates if they used phospholipids for all membranes (i.e. the membranes of grana in chloroplasts)ii. Structure1. Glycerol backbone2. Fatty acids linked to Carbons 1 and 2 via ester bonds3. Head group attached to Carbon 3 via glycosidic linkagesiii. Properties1. Different fatty acids and head groups change the properties of the lipids (i.e. solubility in organics or aqueous solvents, polarity, etc)2. Carbon 1 is often saturated while Carbon 2 is typically the one with one or more double bonds (mono- or poly-unsaturated)iv. Function1. Abundant in chloroplasts (galactolipids and sulfolipids are the most abundant membrane lipids)2. Compensate for the phosphate limitation in plants.c. Sphingolipidsi. Structure1. Built on the amino alcohol ‘sphingosine’a. Amino group on Carbon 2b. Hydroxyl group and a trans double bond in the sphingosinestructure on Carbon 3c. A fatty acid is attached to the nitrogen on Carbon 2 via an amide bondd. Polar head group attached to Carbon 1ii. Properties1. Different fatty acids and head groups change the properties of the lipids (i.e. solubility in organics or aqueous solvents, polarity, etc)a. Look at table on pg. 9 in the class notes for the structures of different polar head groups and the names of different sphingolipidsiii. Functions1. Though sphingolipids, like ganglioside GM2, are small portion of the components in membranes, they help identify cells for cell to cell communication2. Key for cell recognition (i.e. determining ABO blood type)3. Sphingolipids are prevalent in the myelin sheath and other neuronal membranes4. Though sphingolipids are very low in concentration, problems withturn over/break down are seriousa. i.e. an inability to break down gangliosides results in Tay Sachs disease.d. Cholesterol (an Isoprenoid)i. Structure1. A steroid nucleus formed of 4 rigid, fused rings that are planar in structure.2. Hydrocarbon tail3. Hydroxyl group on Carbon 34. Root structure is Isoprene (there are no fatty acids)ii. Properties1. Amphipathic (the hydrocarbon rings and the tail are hydrophobic; the OH- is polar)2. Rigid (due to the rings)a. Rigidity has implications on how cholesterol behaves in membranes by impacting membrane fluidityi. Membranes without cholesterol have a sharp transfer to liquid state when temperature increasesii. Cholesterol maintains fluidity over a higher range oftemperatures (the rings keep the phospholipids from packing in as close so the membrane stays more fluid at low temps; the rigidity of the rings adds stability to the membrane at higher temps because it cannot rotate like fatty acids do)b. Cholesterol is a hormone/signaling precursor (i.e. testosterone, estradiol)c. Cholesterol is a bile acid precursor (i.e. taurocholic acid)i. Bile acid cells form complex micells that work to break up lipids so they can be digested.e. Isoprenoidsi. Like cholesterol, other molecules are formed from an
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