Fatty acids play key roles in metabolism as fuels, for energy storage and transport, and as components of cell membranes. They are classified by their level of saturation. Saturated fatty acids have no double bonds while unsaturated fatty acids have one or more double bonds. The structure of fatty acids consists of a carboxyl end, alpha and beta carbons, and an omega methyl end. Fatty acids are broken down through beta-oxidation to produce acetyl-CoA for energy. They can also undergo lipid peroxidation or saponification.

1. Fatty acids
 Fatty acids, both free and as part of complex lipids,
play a number of key roles in metabolism
1. major metabolic fuel
2. storage and transport of energy
3. as essential components of all membranes
4. gene regulators

2.  In addition,
1. dietary lipids provide polyunsaturated fatty acids
that are precursors of powerful locally acting
metabolites, i.e. the eicosanoids.
2. As part of complex lipids, fatty acids are also
important for thermal and electrical insulation,
and for mechanical protection.

3.  Moreover, free fatty acids and their salts may
function as detergents and soaps owing to their
amphipathic properties and the formation of
micelles.

4. Structure of fatty acids
 Fatty acids are synthesized from linear acetogenins
of acetate pathway
 Fatty acids are carbon chains with a methyl group at
one end of the molecule (designated omega, ω) and
a carboxyl group at the other end.

5.  The carbon atom next to the carboxyl group is called the α
carbon, and the subsequent one the β carbon
 The systematic nomenclature for fatty acids may also
indicate the location of double bonds with reference to the
carboxyl group (Δ).

6.  CH3 – (CH2 )n CH2 – CH2 – COOH
ω β α
 Fatty acids may be named according to systematic or
trivial nomenclature.
 One systematic way to describe fatty acids is related to
the methyl (ω) end. This is used to describe the position
of double bonds from the end of the fatty acid.

7. Classification
 Fatty acids are classified depending on the saturation
01) Saturated fatty acids
 Saturated fatty acids are ‘filled’ (saturated) with hydrogen –
no double bonds
 Most saturated fatty acids are straight hydrocarbon chains
with an even number of carbon atoms.
 The most common fatty acids contain 12–22 carbon atoms.

8. Unsaturated fatty acids
 Monounsaturated fatty acids have one carbon–
carbon double bond, which can occur in different
positions.
 The most common monoenes have a chain length of
16–22 and a double bond with the cis configuration.

9.  This means that the hydrogen atoms on either side of the
double bond are oriented in the same direction.
 Trans isomers may be produced during industrial
processing (hydrogenation) of unsaturated oils and in the
gastrointestinal tract of ruminants.

10. Short chain saturated fatty acids
 Bad smell
 Fluids
 Present in milk fat (C4-C10)
 Easily digestible
Long chain saturated fatty acids
• Solid at room temperature
• Most common in animal and plant fats
• Less easily digestible

11.  The presence of a double bond causes restriction in
the mobility of the acyl chain at that point.
 Cis fatty acids are thermodynamically less stable
than the trans forms.
 The cis fatty acids have lower melting points than
the trans fatty acids or their saturated counterparts.

12.  In polyunsaturated fatty acids (PUFAs) the first double
bond may be found between the third and the fourth
carbon atom from the ω carbon; these are called ω-3 fatty
acids.
 If the first double bond is between the sixth and seventh
carbon atom, then they are called ω-6 fatty acids.
 The double bonds in PUFAs are separated from each
other by a methylene grouping.

13.  PUFAs, which are produced only by plants and
phytoplankton,are essential to all higher organisms,
including mammals and fish.
 ω-3 and ω-6 fatty acids cannot be interconverted,
and both are essential nutrients.
 PUFAs are further metabolized in the body by the
addition of carbon atoms and by desaturation
(extraction of hydrogen).

14.  Mammals have desaturases that are capable of removing
hydrogens only from carbon atoms between an existing
double bond and the carboxyl group .
 β-oxidation of fatty acids may take place in either
mitochondria or peroxisomes.

15. Physical properties
 Fatty acids are poorly soluble in water in their
undissociated (acidic) form, whereas they are
relatively stable as potassium or sodium salts
 Thus, the actual water solubility, particularly of
longer-chain acids, is often very difficult to determine
since it is markedly influenced by pH

16.  Fatty acids are easily extracted with nonpolar solvents from
solutions or suspensions by lowering the pH to form the
uncharged carboxyl group.
 In contrast, raising the pH increases water solubility through
the formation of alkali metal salts, which are familiar as
soaps.
 Soaps have important properties as association colloids and
are surface active Agents.

17. Physical Properties of Saturated Fatty Acids
Saturated fatty acids have:
 Molecules that fit closely together in a regular pattern
 Strong attractions (dispersion forces) between fatty acid
chains
 High melting points that makes them solids at room
temperature.

18. Physical Properties of Unsaturated Fatty Acids
Unsaturated fatty acids have:
 Nonlinear chains that do not allow molecules to pack closely
 Weak attractions (dispersion forces) between fatty acid chains
 Low melting points and so are liquids at room
temperature

19. Triacylglycerols
 Triacylglycerols (also called triglycerides) are tri-fatty acid
esters of glycerol
 Triacylglycerols are the major form of fatty acid storage in
plants and animals
 Triacylglycerols can be classified as fats or oils
- fats are solid at room temperature and most come from
animals
- oils are usually liquid at room temperature and come from
plants (palm and coconut oils are solids at room temperature)

21.  Hydrogenation converts alkenes to alkanes
 So, hydrogenation of unsaturated oils produces saturated
fats
 Hydrogenation is typically carried out by bubbling H2 gas
through the heated oil, in the presence of a metal catalyst
(such as nickel or platinum)
 Unsaturated oils are usually only partially hydrogenated, so
that the product is not completely saturated, giving a soft
semisolid fat such as margarine
Hydrogenation of Unsaturated Oils

22. Pt
CH2 O C
O
(CH2)16CH3
CH2 O C
O
(CH2)16CH3
CH O C
O
(CH2)16CH3
+3H2
CH
CH2
O C
O
(CH2)7CH CH(CH2)7CH3
O C
O
(CH2)7CH CH(CH2)7CH3
CH2 O C
O
(CH2)7CH CH(CH2)7CH3

23. Cis and Trans Unsaturated Fatty Acids
 Natural unsaturated fatty acids have cis double bonds
 When unsaturated vegetable oils are hydrogenated to form
more saturated oils (as in margarine), some of the cis fatty
acids are isomerized to trans fatty acids

24.  Trans fatty acids are much more linear than cis fatty acids,
so their melting points are higher and studies have shown
that trans fats may act similarly to saturated fats and could
contribute to heart disease and some cancers

26. Nomenclature of fatty acids
Systematic name:
SATURATED: parent hydrocarbon + oic
e.g. C18: Octadecanoic acid
UNSATURATED: with one double bond: + enoic
e.g. C18: Octadecenoic acid
with two double bonds: + dienoic
e.g.C18: Octadecadienoic acid
with three double bonds: + trienoic
e.g. C18: Octadecatrienoic acid

27. Saturated
Common Systematic
 C16:0 Palmitic n-Hexadecanoic
 C18:0 Stearic n-Octadecanoic
Unsaturated
Common Systematic
 C16:1(9) Palmitoleic cis-9-Hexadecenoic
 C18:2(9,12) Linoleic cis-9,trans-12 -
Octadecadienoic
 C18:3(9,12,15) Linolenic all cis-9,12,15-
Octadecatrienoic

28.  UNSATURATED – counting from
carboxy end methyl (ω) end:
 C16:1(9) Palmitoleic 16:1, n-7 (ω7)
 C18:1(9) Oleic 18:1, n-9 (ω9)
 C18:2(9,12) Linoleic 18:2, n-6 (ω6)
 C18:3(9,12,15) Linolenic 18:3, n-3 (ω3)
 C20:4(5,8,11,14) Arachidonic 20:4, n-6 (ω6)

30. Availability
 Over half of the fatty acid residues of plant and animal lipids
are unsaturated and are often polyunsaturated.
 Bacterial fatty acid residues are rarely polyunsaturated but
are commonly branched, hydroxylated, or contain
cyclopropane rings.

31.  Unusual fatty acids such as hydroxy fatty acids also occur
as components of the oils and waxes (esters of FAs and long
chain alcohols) produced by certain plants.

32.  There are more than 100 different FAs in nature
and most FAs have an even number of carbon atoms
(mainly due to the mechanism of biosynthesis-the
concatenation of C2 units)
 Mainly present in the form of esters (not free)

33.  In higher plants and animals, the predominant FA residues
are those of the C16 and C18 species(palmitic, oleic,
linoleic, and stearic acids).
 FAs with less than 14 and more than 20 carbonatoms are
uncommon

34. BRANCHED FAs
 Of plant origin, not synthesized in mammalian
organisms
 E.g. Phytanic acid (in cow milk) – oxidation product
of phytol(part of chlorophyl)
3,7,11,15 Tetramethylhexadecanoic acid
– In sebaceous glands

35. – Failure to degrade phytanic acid - Refsum disease:
– deposits of the phytanic acid can be found in the nervous
system –neurological disorders of cerebellum, periferal
nerves,eyes
– Prevention: phytanic acid-free food

36. Metabolism of fatty acids
 Lipolysisis carried out by lipases.
 Once freed from glycerol, free fatty acids can enter
blood and muscle fiber by diffusion.
 Beta oxidation splits long carbon chains of the fatty
acid into acetyl CoA, which can eventually enter the
TCA cycle – generates energy

37. Briefly, β-oxidation or lipolysis of free fatty acids is
as follows:
 Dehydrogenation by acyl-CoA dehydrogenase,
yielding 1 FADH2
 Hydration by enoyl-CoA hydratase

38.  Dehydrogenation by 3-hydroxyacyl-CoA dehydrogenase,
yielding 1 NADH
 Cleavage by thiolase, yielding 1 acetyl-CoA and a fatty acid
that has now been shortened by 2 carbons (acyl-CoA)

39.  This cycle repeats until the FFA has been completely
reduced to acetyl-CoA or, in the case of fatty acids with
odd numbers of carbon atoms, acetyl-CoA and 1 mol of
propionyl-CoA per mol of fatty acid.

40. Lipid peroxidation
 Lipid peroxidation refers to the oxidative degradation of
lipids.
 It is the process in which free radicals "steal" electrons from
the lipids in cell membranes, resulting in cell damage.
 This process proceeds by a free radical chain reaction
mechanism.

41.  It most often affects polyunsaturated fatty acids, because
they contain multiple double bonds in between which lie
methylene bridges (-CH2-) that possess especially reactive
hydrogens

42.  As with any radical reaction, the reaction consists of
three major steps: initiation, propagation, and
termination.

43.  If not terminated fast enough, there will be damage
to the cell membrane, which consists mainly of
lipids.
 Phototherapy may cause hemolysis by rupturing red
blood cell membranes in this way.
 In addition, end-products of lipid peroxidation may
be mutagenic and carcinogenic.

44.  For instance, the end-product malondialdehyde reacts with
deoxyadenosine and deoxyguanosine in DNA, forming
DNA adducts to them

45. Oxidation of Unsaturated Oils
 Fats and oils can become rancid in two ways:
- bacterial ester hydrolysis
- air oxidation of alkenes
 Oxidation of fatty acid alkenes involves cleavage of the
double bonds to form short-chain carboxylic acids
 These oxidation products are foul-tasting and smell badly
OH
O
O2 or O3
OH
O
+
OH
O
HO
O

46.  Fats and oils contain ester groups which can be hydrolyzed
with aqueous acid, aqueous base (saponification) or enzymes
 The hydrolysis products are glycerol and three fatty acids
 When triacylglycerols containing short-chain fatty acids are
hydrolyzed the carboxylic acid products (such as butanoic
and hexanoic acids) are foul-smelling and foul-tasting
(rancid)
HC
H2C
H2C
O C (CH2)14CH3
O
O C
O
(CH2)14CH3
O C (CH2)14CH3
O
H3O+
or
lipase
HC
H2C
H2C
OH
OH
OH
+ HO C (CH2)14CH3
O
3

47. Saponification
 When a triacylglycerol is hydrolyzed with a strong base the
process is called saponification
 The products of saponification are glycerol and fatty acid salts
(soap)
- NaOH is used with saturated fats to produce hard soaps
- KOH is used with unsaturated fats to produce softer, more
liquid soaps
HC
H2C
H2C
O C (CH2)14CH3
O
O C
O
(CH2)14CH3
O C (CH2)14CH3
O
HC
H2C
H2C
OH
OH
OH
+ O C (CH2)14CH3
O
3
NaOH
Na
(Soap)

48. Uses of fatty acids
 Fatty acids are widely used as inactive ingredients in drug
preparations, and the use of lipid formulations as the carriers
for active substances is growing rapidly.
 The largest amount of lipids used in pharmaceuticals is in
the production of fat emulsions, mainly for clinical nutrition
but also as drug vehicles.

49.  Another lipid formulation is the liposome, which is a lipid
carrier particle for other active ingredients.
 In addition, there has been an increase in the use of lipids
as formulation ingredients