Terms in this set (80)
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.
Why are lipids hydrophobic?
Large portion of their structure is hydrocarbon.
What are the functions of lipids
formation of membrane structures
What are the types of lipids
Contain fatty acids:
triacylglycerols, glycerophospholipids, waxes, prostaglandins.
Do not contain fatty acids: steroids.
What are membranes
the partitions that divide compartments from one another and separate the cell from its surrounding.
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.
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 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.
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 structure of fatty acid.
A hydrophilic carboxylate group at one end of the hydrocarbon chain, which contains typically 12-24 carbons.
What are the two types of fatty acid
Saturated fatty acid
Unsaturated fatty acid
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 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 unsaturated fatty acid?
contain one or more double bonds.
liquid at room temperature.
e.g. oleic acid.
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.
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 are the two orientations of double bonds in unsaturated fatty acids?
What does cis-double bond do to the hydrocarbon chain?
cis double bond inserts a bend into the hydrocarbon chain.
Can the bonds in hydrocarbon chain rotate?
Each single bond in the hydrobarbon chain is free to rotate.
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 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 does the nomenclature of the fatty acid 20:4c^5,8,11,14 tell you.
4 cis-double bonds
Double bonds at C5, C8, C11, C14
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.
What is w-3 fatty acid?
double bond at the third C atom from the w carbon.
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.
Why do fatty acids behave like amphipathic substances when dissolved in water?
due to the hydrophilic charge and the long hydrophobic tail.
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 is micelles?
The hydrocarbon tails cluster together within the structure and the carboxylate heads are in contact with the surrounding water.
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.
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.
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.
What are fats called
triacylglycerols or triglycerides
What are triacylglycerols formed of?
triesters of fatty acids and glycerol.
What are simple fats?
triacylglycerols with the same fatty acid esterified at each position.
What are mixed fats?
contain a mixture of fatty acids, often including unsaturated ones.
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 do olive oil contain?
high percentage of oleic acid, which is a monounsaturated fatty acid with one cis double bond.
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.
How is trans fat formed?
Hydrogenation reduces double bonds to single bonds, but may convert cis double bonds to trans double bonds.
Why are triacylglycerols water insoluble?
esterification with glycerol diminishes the hydrophilic character of the head groups of the fatty acids.
What are adipocytes?
animal cells specialized for fat storage. Almost the entire volume of each cell is filled by a fat droplet.
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 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.
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 features of waxes?
High melting points.
What are waxes for?
protective waterproof coating on leaves, fruits, animal skin, fur, feathers and exoskeletons.
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 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.
Why is glycerol an example of a prochiral molecule?
it has no stereocenter until it is derivitized.
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 phosphatidates
glycerophospholipids with two fatty acid groups esterified to C1 and C2 of glycerol 3- phosphate
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.
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.
What is R1
acyl side chains derived from the fatty acids.
What is R2
acyl side chains derived from the fatty acids.
What is R3
hydrophilic R3 head group.
Confers the greatest variation in properties among the glycerophospholipids.
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 the structure of sphingolipids?
long-chain hydrophobic tail.
What is required to make sphingolipids suitable as a membrane lipid?
the addition of only one fatty 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 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 sphingomyeline.
Modification of sphingolipid by addition of groups to the C1 hydroxyl of sphingosine.
phosphocholine group attached to the C3 hydroxyl.
What are the three major membrane lipids
What is glycosphingolipids
lipids containing saccharide groups.
What is included in glycosphingolipids?
cerebrosides (monoglycosyl ceramides) and gangliosides (anionic glycosphingolipids containing one or more sailic acid residues.
Which polar lipid compound is the most abundant
glycoglycerolipids. constitutes about half the lipid in chloroplast membrane.
also abundant in archaea.
What is cholesterol
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 is the structure of cholesterol
Has methyl CH3- groups, alkyl chain, and -OH attached to the steroid nucleus.
What are steroids?
include a number of important hormones (e.g. sex hormones).
Important in cell signaling.
What is the structure of a steroid nucleus
3 cyclohexane rings.
1 cyclopentane ring
no fatty acid.
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 effects does cholesterol have on the membrane
affect membrane stiffness and permeability.
Modulates the fluidity of mammalian cell membranes.
What are eicosanoids?
signaling molecules derived from lipids, which are derived from arachidonic acid.
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 cholesterol converted to cholesterol esters
for cell storage or transport in blood.
How does cholesterol convert to cholesterol esters
fatty acid is esterified to C3 OH of cholesterol.
Why does cholesterol ester help transport
very water-insoluble and must be complexed with phospholipids or amphipatic proteins for transport.
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 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 are steroid hormones?
chemical messengers in cells.
produced from cholesterols.
include sex hormones such as testosterone and estrogen.
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