Lipids

What is the average pKa of fatty acids?

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

What is the differences between waxes and fats?

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).

What are the characteristics of 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.

What is the structure of cholesterol

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

What is hydrogenation for?

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.

What is R1

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

What is R2

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

What effects does cholesterol have on the membrane

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

What are adipocytes?

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

How does the sn system in naming

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.

How is trans fat formed?

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

What is saponification?

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.

How does cholesterol convert to cholesterol esters

fatty acid is esterified to C3 OH of cholesterol.

Why is cholesterol converted to cholesterol esters

for cell storage or transport in blood.

What are phosphatidates

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

Which polar lipid compound is the most abundant

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

What do olive oil contain?

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

What are the possible structures of the hydrocarbon chains?

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

What is R3

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

What are the features of waxes?

hydrophobic. water-insoluble. High melting points.

What are steroids?

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

What is glycosphingolipids

lipids containing saccharide groups.

What are the features of cellular membranes

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

What are eicosanoids?

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

Why can you yield more energy from fat than carbohydrate?

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.

Why do most naturally occurring fatty acids have an even number of carbon atoms

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

What is the net charge on a phospholipid?

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

What is w-3 fatty acid?

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

What are fats called

triacylglycerols or triglycerides

Why do fatty acids behave like amphipathic substances when dissolved in water?

due to the hydrophilic charge and the long hydrophobic tail.

What are the functions of lipids

energy storage signalling formation of membrane structures

Why are triacylglycerols water insoluble?

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

What is included in glycosphingolipids?

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

What is the conformation of the fused cyclohexane rings in cholesterol

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

What are steroid hormones?

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

What does cis-double bond do to the hydrocarbon chain?

cis double bond inserts a bend into the hydrocarbon chain.

What are the two orientations of double bonds in unsaturated fatty acids?

cis- trans-

What are mixed fats?

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

What is unsaturated fatty acid?

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

What gives the rancid odor of spoild fats?

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

What are the three major membrane lipids

phospholipids sphingolipids glycosphinogolipids.

How to define the carbon atoms in the two -CH2OH groups

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

What are waxes for?

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

Where can you find lipids in living organisms

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).

What are the features of saturated fatty acids?

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).

What is micelles?

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

What do sphingolipids contain

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

What is cholesterol

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.

What does the nomenclature of the fatty acid 20:4c^5,8,11,14 tell you.

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

What is the structure of a steroid nucleus

3 cyclohexane rings. 1 cyclopentane ring no fatty acid.

How does lipid form the bilayer membrane?

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.

What is the structure of fatty acid.

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

Why is cholesterol ester more hydrophobic than cholesterol?

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

What are the types of lipids

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

Can the bonds in hydrocarbon chain rotate?

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

What are the functions of fat storage in animals?

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

What can R-glycerol phosphate also be described

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

Why are lipids hydrophobic?

Large portion of their structure is hydrocarbon.

What is sphingomyeline.

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

What are the interactions that hold lipid molecules in water together?

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

What are the two types of fatty acid

Saturated fatty acid Unsaturated fatty acid

How do lipids form membrane in aqueous solutions?

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

What is the importance of eicosanoids?

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

Why is glycerol an example of a prochiral molecule?

it has no stereocenter until it is derivitized.

How do nutritionists name fatty acids?

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

Why are saturated fat solid at room temperature.

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.

What is the structure of sphingolipids?

long-chain hydrophobic tail.

What are glycerophospholipids?

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.

What is formed at the air-water interface

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

What are bile salts?

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.

What is required to make sphingolipids suitable as a membrane lipid?

the addition of only one fatty acid.

Why are unsaturated fat liquid at room temperature?

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

What is saturated fatty acid?

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

what are ceramides

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.

What will happen if fatty acids are mixed with water and an oily substance?

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

What are membranes

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

Why are long hydrocarbon chains of fatty acids efficient for energy storage?

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

What are simple fats?

triacylglycerols with the same fatty acid esterified at each position.

What are triacylglycerols formed of?

triesters of fatty acids and glycerol.

Why does cholesterol ester help transport

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