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Lecture 17

MBIO 2360 Lecture 17: Lecture 17 – MBIO
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Department
Microbiology
Course
MBIO 2360
Professor
Mc Kenna Sean
Semester
Fall

Description
Lecture 17 – MBIO/CHEM 2360 Common Fatty Acids  Saturated:  Note, COOH carbon is number 1  0 refers to the number of double bonds  C2:0 - acetic  C10:0 - capric  C12:0 -lauric  C16:0 - palmitic  -26% of human fat  C18:0 - stearic  5% of human fat  Unsaturated - all cis  9C16:1 - palmitoleic  9c18:1 - oleic  46% of human fat  9,12C18:2 - linoleic  6,9,12C18:3 - gamma-linolenic  9,12,15C18:3 - alpha - linolenic  The first number refers to the location of the double bond Properties of Fatty Acids 1. pKa about 4.5-5 1. at pH 7, the carboxyl group is deprotonated 2. Melting point 1. Increases with the increasing chain length and decreases as number of double bond increases 2. There properties are important in membrane structures where fluidity or stiffness is determined by composition 2. Solubility 1. Fatty acids are water-soluble up to c6 and then only in non-polar solvents 2. Amphipathic 1. Charged head group and a hydrophobic tail 2. Structure 1. Formation of micelles  Because fatty acids are amphipathic, in an aqueous environment, the hydrophobic components interact with each other and they hydrophilic component interacts with the water for form micelles o Draw Lipids  Fatty acids are a component of many lipids  Two main types o Storage lipids - neutral  How we store fat in the body - for energy o Membrane lipids - polar Storage Lipids  The simplest lipids constructed from fatty acids are the neutral triacylglycerol fats (also called triglycerides) o These are esters of glycerol with fatty acids  Uses ester linkages o Mono, di, and tri acylglycerols occur, but the most widespread are the triacylglycerols (3 fatty acyl units)  Draw glycerol  And draw triacylglycerol  R1 2 and 3 can all be the same  Tristearoylglycerol (tristearin) where R=c18  They can also be different Properties and some functions of triacylglycerols 1. Melting point variation is similar to those of single fatty acids, increasing with chain length and with decrease unsaturation 2. Triglycerides are the most abundant family of lipids: the fats and oils 1. Fats are less unsaturated and oils more unsaturated 2. Energy storage, fall cells (adipocytes), oil seeds (canola, sunflower) 1. Since the C is more reduced than in carbohydrate, fat has about 2 times as much energy per unit mass 2. Insulation - stored under the skin in seals, walruses, penguins, and humans 3. Buoyancy - sperm whales change their buoyancy at different depths as spermacetic oil density changes with temperature Fatty Acid composition of some triglycerides  A liquid fat has a lot more unsaturated fat  Harder fat has more saturated fat Soap  Draw  TAG - triacylglycerol  This process is called saponification - soap-making o The fatty acid products form micelles in water, which can carry oil in their interiors and still be soluble in water o This is how soap works to remove greasy dirt  Intestinal lipases catalyze enzymatic hydrolysis of TAGs Membrane Lipids (Polar) 1. Glycerophospholipids  Derivatives of phosphatidic acid  Diacylglycerolphosphate  Glycerol backbone, 2 fatty acids, and a phosphate  The phosphate is on the 3rd Carbon on the glycerol  One of the O on the phosphate as another group on it - a head group  Draw The most Common head groups  -CH2-Ch2-NH3+ - phosphatidylethanolamine  -CH2-Ch2-N+(CH3)3 - phosphatidylcholine (lecithin)  Formula - phosphatidylserine  When X= ethanolamine or choline, the compound is zwitterionic,  When X=serine, the net charge is -1  Phospholipids are amphipathic compounds, with both polar and non-polar functions, so they form a bilayer due to the hydrophobic effect  This allows them to assemble into membranes  Phosphatidyl choline  Draw  Results in the molecules having a polar head and a nonpolar tail  Curved bilayers can form vesicles and liposomes  Micelle - individual units are wedge-shaped  The head group is much bigger than the tail  Bilayer - individual units are cylindrical  Liposomes - have an aqueous cavity  Specific pho
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