CHE 350 Lecture Notes - Lecture 13: Spectrin, Phylloquinone, Glycolipid
Lipids = not polymeric, but they aggregate this is how they perform their central function as
the structural matrix of biological membranes
Lipids = largely hydrophobic and only sparingly soluble in water. In general, they perform 3
basic biological functions
1. Lipid molecules in the form of lipid bilayers are essential components of biological
membranes
2. Lipids containing hydrocarbon chains serve as energy stores
3. Many intra- and intercellular signaling events involve lipid molecules
1 | Lipid Classification
A – The Properties of Fatty Acids Depend on Their Hydrocarbon Chains
Fatty acids = carboxylic acids with long-chain hydrocarbon side groups
In higher plants and animals, the predominant fatty acid residues are those of the C16 and
C18 species – palmitic, oleic, linoleic, and stearic acids
Fatty acids with <14 or >20 carbon atoms are uncommon
Fatty acids have an even number of carbon atoms because they are biosynthesized by the
concatenation of C2 units
Majority of fatty acid residues of plant/animal lipids = unsaturated (double bonds)
oOften polyunsaturated (two or more double bonds)
oBacteria fatty acids rarely polyuns, commonly branched, hydroxylated, or
contain cyclopropane rings
Usually first double bonds b/w C9 and C10 counting from the carboxyl C atom
oCalled ∆9- or 9-double bond
In polyuns fatty acids, double bonds tend to occur at every third carbon atom so NOT
conjugated
oImportant polyuns fatty acids are ω-3 or ω-6 (OMEGA) fatty acids ID’s the last
double-bonded carbon atom counted from the methyl terminal (ω, omega, end
terminal) end of the chain
Fatty acid double bonds almost always have cis configuration
oPuts a rigid 30 degree bend in hydrocarbon chain
oUnsaturated fatty acids pack together less efficiently than saturated fatty acids
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Reduced Van der Waals forces of unsaturated fatty acids cause melting
points to decrease with the degree of unsaturation
More unsaturation = more reducing of forces = lower MP
oFluidity of lipids containing fatty acid residues likewise increases with the degree
of unsaturation of the fatty acids
More unsaturation = more fluidity
Trans fats = cardiovascular disease
oDouble bonds in unsaturated fats slowly reacts w/ oxygen in air to yield aldehydes
and carboxylates of shorter chain length, whose increased volatility = gross smell
oIncrease stability by partially hydrogenating (treat with H2 in presence of metallic
catalyst at high temp and pressure [from org 1])
Eliminates some double bonds, increases melting temp
Converts some cis bonds to trans double bonds = trans fats
oEating a lot of trans fats = large increase in cardiovascular disease via increasing
levels of cholesterol in the blood
Saturated fatty acids = fully reduced, saturated with H’s
oHighly flexible, assumed a wide range of conformations due to relatively free
rotation around C-C bonds.
oLowest energy conf is the fully extended con, least amount of steric interference
b/w neighboring methylene groups
oMelting points of saturated fatty acids increases w/ molar mass
B – Triacylglycerol’s Contain Three Esterified Fatty Acids
Fats and oils that occur in plants and animals are largely triacylglycerol’s (triglycerides)
oNonpolar, water-insoluble, fatty acid triesters of glycerol
Function = energy reservoirs in animals = most abundant class of lipids even though they
aren’t components of cellular membranes
Triacylglycerols differ according to the identity and placement of their three fatty acid
residues
o–ate ending –oyl ending
Fats are a highly efficient form in which to store metabolic energy
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oTriacyls are less oxidized than carbs or proteins so they yield more energy per
unit mass on complete oxidation
oSince they’re nonpolar, they’re stored in anhydrous form, whereas glycogen binds
about twice its weight of water under physio conditions fats provide about six
times the metabolic energy of an equal weight of hydrated glycogen
oIn the human body, adipose (fat tissue) = surviving starvation for 2-3 months =
LONG TERM energy. Body’s glycogen supply functions as SHORT TERM
energy, provides for body’s energy needs for less than a day. Fat also = warmth.
C – Glycerophospholipids (Phosphoglycerides) Are Amphiphilic
Major lipid components of biological membranes
Also originates from glycerol made from glyercol-3-phosphate
oC1 and C2 positions esterified with fatty acids
oPhosphoryl group is linked to another polar group usually (X)
oGlycerophospholipids are therefore amphiphilic molecules with nonpolar
aliphatic (hydrocarbon) “tails” and polar phosphoryl-X “heads”
Simplest glycerophospholipids X = H
oThey are phosphatidic acids – present in only small amounts in biological
membranes
The ones that commonly occur in bio membranes, the head groups are derived from polar
alcohols
oSaturated C16 or C18 fatty acids usually occur at the C1 position of the
glycerophospholipids, and the C2 position is often occupied by an unsaturated
C16-C20 fatty acid.
Individual ones are named by the identities of the fatty acid residues.
Phospholipases Hydrolyze Glycerophosphos
oChemical structures of glycerophosphos can be determined from the products of
the hydrolytic reactions catalyzed by phospholipases (enzymes)
oPhospholipases make lysophospholipids, which are powerful detergents that
disrupt cell membranes = lysing cells
oEnzymes that act on lipids must gain access to portions of the lipids that are
buried in a nonaqueous environment
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Document Summary
Lipids = not polymeric, but they aggregate this is how they perform their central function as the structural matrix of biological membranes. Lipids = largely hydrophobic and only sparingly soluble in water. A the properties of fatty acids depend on their hydrocarbon chains. Fatty acids = carboxylic acids with long-chain hydrocarbon side groups. In higher plants and animals, the predominant fatty acid residues are those of the c16 and. C18 species palmitic, oleic, linoleic, and stearic acids. Fatty acids with <14 or >20 carbon atoms are uncommon. Fatty acids have an even number of carbon atoms because they are biosynthesized by the concatenation of c2 units. Majority of fatty acid residues of plant/animal lipids = unsaturated (double bonds: often polyunsaturated (two or more double bonds, bacteria fatty acids rarely polyuns, commonly branched, hydroxylated, or contain cyclopropane rings. Usually first double bonds b/w c9 and c10 counting from the carboxyl c atom: called 9- or 9-double bond.
