Lipids 1. Storage Lipids 2. Structural Lipids in Membranes 3. Working with Lipids

Storage Lipids Fatty Acids - Structure Fatty Acids - Physical Properties Triacylglycerols - the simplest Lipids Triacylglycerols in Energy Storage Thermal insulation Triacylglycerols in food Waxes

Fatty Acid Structure Carboxylic Acids (COOH is C1) hydrocarbon tails (C4 - C36) Saturated fatty acids N:0 Unsaturated Fatty acids Double bonds specified by (Δ n ) Branched or unbranced

Fatty Acid Structure Carboxyl group (COOH) forms the acid. “R” group is a hydrocarbon chain.

A Representative Fatty Acid

Saturated Fatty Acid Unsaturated Fatty Acid

Fatty Acids - Physical Properties Solubility Longer chains more hydrophobic, less soluble Double bonds increase solubility Melting points Depend on chain length and degree of unsaturation Double bonds- low melting temp Ex: At room temperature (25 C), the saturated fatty acids from 12:0 to 24:0 have a waxy consistency, Whereas, unsaturated fatty acids of these lengths are oily liquids.

Triacylglycerols Glycerol head group HO-CH 2 -CH(OH)-CH 2 - OH Ester linkage from each hydroxyl to Fatty acid Carboxylate charge is lost TAGs more hydrophobic than FAs

Synthesis of a Fat

Triacylglycerols in Energy Storage & Thermal insulation In eukaryotic cell: TG as oily droplet in cytosol-metabolic fuel. Vertebrates: adipocyte cell (fat cell) store large amount of TG Oil in seeds, plants: providing energy and biosynthetic precursors for seed germination. Adipocyte cell and germinating seed containing Lipases that hydrolyze the ester linkages to release Fatty Acids

Triacylglycerols in Energy Storage & Thermal insulation Advantages using TG as stored fuels over carbohydrates: Concentrated source of energy –Energy derived from oxidation reactions –More completely reduced state yields 2x the energy/g as Carbohydrates

Triacylglycerols in Energy Storage & Thermal insulation TG as insulator: In some animals, triacylglycerols stored under the skin serve not only as energy stores but as insulation against low temperatures. Ex: Seals, penguins, other warm-blooded polar animals, hybernating animals (bears) etc.

All C bonded to H No C=C double bonds long, straight chain most animal fats solid at room temp. contributes to cardiovascular disease (atherosclerosis) = plaque deposits Saturated fats Triacylglycerols in food

Unsaturated fats C=C double bonds in the fatty acids plant & fish fats vegetable oils liquid at room temperature the kinks made by double bonded C prevent the molecules from packing tightly together Triacylglycerols in food

Saturated vs. unsaturated saturated unsaturated

Triacylglycerols in food Vegetable Oils (ex. Olive oil) :  unsaturated, liquids at room temperature.  converted industrially into solid fats by catalytic hydrogenation, which reduces some of their double bonds to single bonds.

Waxes Esters of long chain fatty Acids with long chain alcohols Higher melting points Hydrophobic

Summary Lipids are water insoluble Common Fatty Acids have carbon atoms (an even number) Triacyl glycerols primary storage fats in food.

Structural Lipids in Membranes Glycerophospholipids Ether Lipids Galactolipids and Sulfolipids in Chloroplasts Archael "Extremophile" Lipids Sphingolipids Lipid Degradation in Lysosomes Sterols Summary Some common types of storage and membrane lipids.

Summary Polar Lipids major constituent of membranes Glycerophospholipids are charged depending on constituents Galactolipids are abundant in chloroplasts Archaebacteria have extreme lipids Sphingolipids are built on a sphingosine framework Sterols have a polycyclic aromatic ring structure

Phospholipids Structure: – glycerol + 2 fatty acids + PO 4 PO 4 negatively charged It’s just like a penguin… A head at one end & a tail at the other!

Phospholipids Hydrophobic or hydrophilic? – fatty acid tails = hydrophobic – PO 4 = hydrophilic head – dual “personality”

Phospholipids in water Hydrophilic heads attracted to H 2 O Hydrophobic tails “hide” from H 2 O – can self-assemble into “bubbles” bubble = “micelle” can also form bilayer early evolutionary stage of cell? bilayer

Why is this important? Phospholipids create a barrier in water – define outside vs. inside – cell membranes

Phospholipids & cells Phospholipids of cell membrane – double layer = bilayer – hydrophilic heads on outside in contact with aqueous solution outside of cell and inside of cell – hydrophobic tails on inside form core – forms barrier between cell & external environment

Phosphatidylcholine, with choline as polar head group, is another glycerophospholipid. It is a common membrane lipid. Phosphatidylinositol, with inositol as polar head group, is one glycerophospholipid. In addition to being a membrane lipid, phosphatidylinositol has roles in cell signaling. Sphingolipids are derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group.

Sterols Have 4 fused rings Cholesterol is the major sterol in vertebrates Steroid Hormones –Testosterone, Estrogen

Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic. Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail.

Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids. The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.

Cholesterol Important cell component – animal cell membranes – precursor of all other steroids including vertebrate sex hormones – high levels in blood may contribute to cardiovascular disease

Cholesterol helps keep cell membranes fluid & flexible Important component of cell membrane

From Cholesterol  Sex Hormones What a big difference a few atoms can make!

Working with Lipids Lipid Extraction Adsorption Chromatography Gas Liquid Chromatography Specific Hydrolysis Mass Spectrometry