Lipids

Generally hydrophobic/ amphipatic. Water-insoluble organic compounds. Do not form large covalent polymers. They tend to associate with each other through noncovelent forces. Polar (hydrophilic) head Nonpolar (hydrophobic) hydrocarbon tail.

Large portion of their structure is hydrocarbon.

energy storage signalling formation of membrane structures

Contain fatty acids: triacylglycerols, glycerophospholipids, waxes, prostaglandins. Do not contain fatty acids: steroids.

the partitions that divide compartments from one another and separate the cell from its surrounding.

selective membrane permeability. establish order by compartmentation. allow free energy to be stored in the form of concentration gradients.

rarely found free in solution, they are either in complex with soluble protein transporters, or part of higher order assemblies that sequester the hydrophobic surface area from the surrounding aqueous environment. (associate to form water-soluble structures, such as micelles, vesicles, and bilayers).

Noncovalent interactions between lipid molecules. Interaction between nonpolar tails by hydrophobic effect. van der Waals interaction between the hydrocarbon regions of the molecules.

The polar, hydrophilic head groups of membrane lipids associate with water, allow the formation of surface monolayers, bilayers, micelles, and vesicles.

A hydrophilic carboxylate group at one end of the hydrocarbon chain, which contains typically 12-24 carbons.

Saturated fatty acid Unsaturated fatty acid

the carbons of the tail are all saturated with hydrogen atoms. No double bonds. e.g. Stearic acid.

single C-C bonds. molecules fit closely together in a regular pattern. Strong attractions between fatty acid chains. High melting points (solid at room temperature).

contain one or more double bonds. liquid at room temperature. e.g. oleic acid.

long saturated chains can pack closely together, thereby increasing the number of van der Waals contacts to form regular, semicrystalline bonds. Longer chains, higher melting points, more solid.

the bends imposed by one or more cis double bonds make the molecule pack less regular, thus more dynamic.

cis- trans-

cis double bond inserts a bend into the hydrocarbon chain.

Each single bond in the hydrobarbon chain is free to rotate.

They are synthesized by sequential additions of a two carbon precursor.

hydrocarbon chains are linear in most fatty acids. Some fatty acids contain branches or even cyclic structures.

20 carbons. 4 cis-double bonds Double bonds at C5, C8, C11, C14

location of C=C bonds: 'omega carbon' w-carbon: the last C atom in the chain. a-carbon: -COO- carbon.

double bond at the third C atom from the w carbon.

Average pKa: 4.5 Fatty acids are weak acids. RCOOH <-> RCOO- + H+ These acids exist in the anionic form (RCOO-) at physiological pH.

due to the hydrophilic charge and the long hydrophobic tail.

monolayers of fatty acid. the carboxylate groups immersed in water and the hydrocarbon tails out of water.

spherical. The hydrocarbon tails cluster together within the structure and the carboxylate heads are in contact with the surrounding water.

the micelles will form around the oil droplets and emulsify them.

they contain carbon in a reduced form and will therefore yield a large amount of energy on oxidation.

They are hydrophobic, fat stores are also anhydrous, whereas glycogen is hydrated. A gram of stored fat yields much more metabolic energy than a gram of stored carbohydrate.

triacylglycerols or triglycerides

triesters of fatty acids and glycerol.

triacylglycerols with the same fatty acid esterified at each position.

contain a mixture of fatty acids, often including unsaturated ones.

Hydrogenation of unsaturated fat oils is used commercially to convert them to firmer fats, which can be used as butter substitutes such as margarine, or to stabilize them against spoilage.

high percentage of oleic acid, which is a monounsaturated fatty acid with one cis double bond.

oxidative cleavage of the double bonds in fats yields volatile aldehydes and carboxylic acids, which contributes to the rancid odor of spoiled fats.

Hydrogenation reduces double bonds to single bonds, but may convert cis double bonds to trans double bonds.

esterification with glycerol diminishes the hydrophilic character of the head groups of the fatty acids.

animal cells specialized for fat storage. Almost the entire volume of each cell is filled by a fat droplet.

Energy production: fat is oxidized to generate ATP. Heat production: some specialized cells oxidize triacylglycerols for heat production. Insulation: thermal insulation.

fats hydrolyzed with strong bases such as NaOH, KOH, producing soap. The fatty acids are released as either sodium or potassium salts, which are fully ionized.

a long chain fatty acid is esterified to a long-chain alcohol. Only has a weakly hydrophilic head group attached to two long hydrocarbon chains (one fatty acid chain, one alcohol chain).

hydrophobic. water-insoluble. High melting points.

protective waterproof coating on leaves, fruits, animal skin, fur, feathers and exoskeletons.

A double tail yields a roughly cylindrical molecule, such cylindrical molecules can easily pack in parallel to form extended sheets of bilayer membranes with the hydrophilic head groups facing outward into the aqueous regions on either side.

major class of naturally occuring phospholipids (lipids with phosphate-containing head groups). The phosphate is esterified to both glycerol and another compound bearing an -OH group. Make up a significant fraction of the membrane lipids.

it has no stereocenter until it is derivitized.

pro-S or pro-R (based on the stereochemistry of the product that results from derivatization of one or the other of these groups.

glycerophospholipids with two fatty acid groups esterified to C1 and C2 of glycerol 3- phosphate

L-glycerol-3-phosphate or D-glycerol-1-phosphate, depending on which carbon is designated as #1.

assign C1 to the pro-S carbon of the glycerol. Following this convention, all glycerophospholipids can be considered to be derivatives of sn-glycerol-3-phosphate.

acyl side chains derived from the fatty acids. often saturated.

acyl side chains derived from the fatty acids. often unsaturated.

hydrophilic R3 head group. Confers the greatest variation in properties among the glycerophospholipids.

a function of the charge (if any) on the R3 group in combination with the negatively charged phosphodiester in the head group.

long-chain hydrophobic tail.

the addition of only one fatty acid.

the class of spingolipids where a fatty acid linked via an amine bond to the NH2 group. Consist of sphingosine (a long-chain amino alcohol) and a fatty acid.

sphingosine (a long-chain amino alcohol), a fatty acid, phosphate, and a small amino alcohol. Have polar and nonpolar regions. Similar to phospholipids.

Modification of sphingolipid by addition of groups to the C1 hydroxyl of sphingosine. phosphocholine group attached to the C3 hydroxyl.

phospholipids sphingolipids glycosphinogolipids.

lipids containing saccharide groups.

cerebrosides (monoglycosyl ceramides) and gangliosides (anionic glycosphingolipids containing one or more sailic acid residues.

glycoglycerolipids. constitutes about half the lipid in chloroplast membrane. also abundant in archaea.

steroids. precursor for many of the steroid hormones and bile salt. Weakly amphiphatic substance due to the hydroxyl group at one end of the molecule.

Has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus.

include a number of important hormones (e.g. sex hormones). Important in cell signaling.

3 cyclohexane rings. 1 cyclopentane ring no fatty acid.

chair conformation. This makes cholesterol a bulky, rigid structure. The cholesterol molecule tends to disrupt regular packing of fatty acid tails in membrane structure.

affect membrane stiffness and permeability. Modulates the fluidity of mammalian cell membranes.

signaling molecules derived from lipids, which are derived from arachidonic acid.

These are potent activators of a wide range of physiological functions, including inflammation, blood clotting, blood pressure regulation, and reproduction.

for cell storage or transport in blood.

fatty acid is esterified to C3 OH of cholesterol.

very water-insoluble and must be complexed with phospholipids or amphipatic proteins for transport.

Carboxyl group react with OH to form ester bond. Hydroxl group gone, no polarity, therefore more hydrophobic.

synthesized in the liver from cholesterol. stored in the gallbladder. secreted into the small intestine. have a polar and nonpolar region. mix with fats to break them apart. emulsify fat particles to provide large surface area.

chemical messengers in cells. produced from cholesterols. include sex hormones such as testosterone and estrogen.