Lipids: What do you need to know? o Classification of major lipid groups o Structure of fatty acids o Physical properties of fatty acids o Structure & function of triacylglycerols o Chemical reactions of triacylglycerols o Compare phospholipids & glycolipids o Composition & properties of membrane lipids o Structure & function of cholesterol o Compare & contrast 3 types of cellular membrane transport o Compare & contrast some steroid hormones o Structure & function of bile acids o Compare & contrast 3 types of eicosanoids o Structure & function of biological waxes Fats and oils are the most widely occurring types of lipids. Thick layers of fat help insulate polar bears against the effects of low temperatures.

A lot of structural variety is represented by lipids. They are typically: - insoluble in H 2 O - soluble in NP solvents

Lipid Categories (based on function) Energy Storage –Triacylglycerols (fats) Membrane structure –Phospholipids, Sphingoglycolipids, cholesterol Emulsification –Bile acids Messenger molecules –Steroid hormones; eicosanoids Protective coating –Biological waxes

Lipid Building Blocks - Fatty Acids (F.A.) Fatty Acids = monocarboxylic acids –Straight chains Long: C 12 -C 26 Medium: C 8 & C 10 Short: C 4 & C 6 –Saturated (SFA) –Monounsaturated (MUFA) –Polyunsaturated (PUFA) Usually </= 6 double bonds –Almost always known by common names

All of these are 18 carbon chains

Various formulas can be used to draw the long chains: e.g. 14 carbons long

Structural Notation for F.A. F.A. With 18 C atoms and 1 double bond (MUFA). F.A.-COOH endMethyl end SFA no ∆ notation no  notation MUFA usually ∆ 9  -3 or  -9 PUFA generally ∆ 9,12,(15)  -3 or  -6

Physical Properties Water solubility decreases with increasing # C atoms MP increases with increasing # C atoms MP decreases with increasing unsaturation –Straight chains pack well –Bent chains don’t pack well Four 18-carbon fatty acids, which differ in the number of double bonds present.

Compounds with double bonds, or rings: Observe attached groups lying above or below plane of double bond or ring. "cis" groups on same side. "trans" groups are across. Different isomers have different physical and sometimes different chemical properties. Quick review of cis/trans isomerism:

Cis pattern creates bent molecules. This affects the intermolecular bonding If there is more than one double bond, they occur at three-carbon intervals. -C=C-C-C=C- This is called the divinylmethane pattern.

Space-filling models of four 18-carbon fatty acids, which differ in the number of double bonds present. Note how the presence of double bonds changes the shape of the molecule.

Common names derive from a common source of the compound or the source from which it was first isolated. e.g.Palmitic acid is found in palm oil Oleic acid - a major part of olive oil (oleum) Stearic (from Greek word for “solid”) acid is solid at room temperature. Spiders (Arachnids) contain arachidonic acid.

In IUPAC system, carboxyl carbon is number one. All bonds reference the carboxyl carbon. e.g. a double bond between 9 th and 10 th C is at the 9-carbon + a Greek name cis- 9- hexadecanoic acid (16 carbons) These names are awkwardly long so aren’t used as commonly as some of the other systems

Essential fatty acids: alpha-linolenic acid (ALA, an omega-3) and linoleic acid (an omega-6) Human body needs, but cannot manufacture, them. When sufficient quantities are supplied in the diet, the body can make enough Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to create the eicosanoids that form our metabolic "thermostat" system Also affect brain development and function. Lack of these can cause: Depression, ADHD, Alzheimers, & Inflammation

Triacylglycerols = Triglycerides = Triesters Adipoctyes are the body’s triacylglycerol- storing cells. Simple mixed

Triple esterification reaction between glycerol and 3 molecules of stearic acid (18:0 fatty acid). Three molecules of water are a by-product of this reaction. Dehydration synthesis (condensation rxn) of a simple Triacylglycerol (triglyceride)

Fats vs. Oils Fats: typically are solids at room temp. –Mostly SFAs –Generally from animals Warm-blooded organisms Fluid at warmer temperatures Oils: typically are liquids at room temp. –Lots of MUFAs and PUFAs –Generally from plants More kinks in the chain, the more fluid the oil. Makes cell membranes flexible and permeable, allowing nutrients in & waste products out.

Lipids & your Diet General population correlation –High triglyceride intake = increased risk of heart disease & certain cancers But... Inuit...,etc. “Good” vs. “Bad” fats –SFA = “Bad” –MUFA = “Good” cold water fish (  -3 FA) –PUFA  -3 = “Good”  -6 = “Bad”