Lipids are a diverse group of hydrophobic organic molecules crucial for energy, structural components of membranes, and various biological functions. They are classified into simple, complex, and derived lipids, with fatty acids, triglycerides, and phospholipids playing significant roles in metabolism and cell structure. Eicosanoids and antioxidants like vitamin E are also important, as they contribute to cellular processes and protect against oxidative damage.

1. LIPID CHEMISTRY
Dr.Charles / Dr Ayyub

2. Introduction
• Lipids are heterogeneous group of water
insoluble (hydrophobic) organic molecules
• They are fats, oils, steroids and waxes
• Insoluble in water, but soluble in non-polar
solvents such as ether, chloroform
• They are important dietary constituents
providing (a) high energy value ( 1 g = 9
kcal) (b) Fat soluble vitamins and (c)
Essential fatty acids

3. Biological importance of Lipids
• Important dietary compounds (Essentitial
fatty acids) and storage form of energy
(Triglycerides)
• Structural components of biomembranes
(phospholipids and cholesterol)
• Providing insulation against changes in
external temperature (subcutaneous fat)
• Giving shape and contour (outline) to the
body
• Protecting internal organs by providing a
cushioning effect (pads of fat)

4. Contd..
• Metabolic regulators (steroid hormones and
prostaglandins)
• Acting as surfactant, detergents and
emulsifying agents (amphipathic lipids)
• Acting as electric insulators in neurons
• Helping in absorption of fat soluble vitamins
(A,D,E, & K)
• With proteins and carbohydrates, they form
important cellular constituents (lipoproteins,
glycolipids)

5. Classification of Lipids
• Lipids are classified into simple, complex and
derived lipids
1.Simple lipids: Esters of fatty acids (FA) with
various glycerol
a. Fats: esters of FA with glycerol (TAG)
b. Waxes: esters of FA with higher
molecular weight alcohols
2. Complex Lipids: Esters of FA containing groups
in addition to an alcohol and a FA
a. Phospholipids: Esters of FA with
alcohol and phosphoric acid.
In glycerophospholipids the alcohol is glycerol
In sphingophospholipids the alcohol is sphingosine

6. Classification contd…..
b. Glycolipids are lipids with carbohydrates
and sphingosine
c. Others complex lipids are lipoproteins
3.Derived Lipids: These include FA, glycerol,
steroids, some alcohols, fatty aldehydes
and ketone bodies.
Acylglycerols (glycerides), cholesterol &
cholesterol esters are termed neutral lipids
because, they are uncharged.

7. LIPIDS

8. A. Fatty acids (FA)
• FA are aliphatic carboxylic acids. Their
chain may be saturated (no double bond)
or unsaturated (contain one or more
double bond)
• Saturated FA end in -anoic ( eg., octanoic)
• Unsaturated FA end in –enoic
(eg.,decaenoic acid or oleic acid)
• Carbon are numbered from the carboxyl
carbon (carbon no 1).
• The carbon atoms adjacent to the carboxyl
carbon (carbon 2,3,4) are also known as
α,β,γ respectively.

9. FA contd…
• The terminal methyl carbon is ‘ω’ or ‘n’
carbon. The position of double bond is
usually indicated by Δ. Δ9 indicates double
bond between 9 and 10 carbon atom or
ω9 indicates the double bond on the ninth
carbon counting from the ω carbon.
9(ω)8 7 6 5 4(γ)3(β)2(α)1
CH3CH2CH2CH2CH2CH2CH2CH2COOH

10. FA contd…
FA may be subdivided into
• Monounsaturated FA containing one double
bond
• Polyunsaturated FA (PUFA) containing two or
more double bonds.
• Linoleic acid (2 double bonds) and Linolenic
acid (3 double bonds) are essential FA because
they cannot be synthesized by the body and
have to be supplied in the diet.
• Eicosanoids are derived from eicosa
(20 carbon) polyenoic fatty acids. Examples are
Leukotrienes (LT) Lipoxins (LX), Prostaglandins
(PG) and Thromboxanes (TX).

11. FA contd…
• Geometric isomerism
occurs at the double
bond depending upon
the orientation of
atoms or groups. If
atoms are on the
same side it is cis
isomer, if on the
opposite side it is
trans isomer. (Fig).
• Naturally occurring
FA are cis isomers.

12. FA contd…
• Triacyl glycerols
(triglycerides) are the
main storage forms of
FA
• The TG are esters of the
trihydric alcohol, glycerol
and fatty acids.
• Cerebronic acid and
ricinoleic acid are
hydroxy fatty

13. Saturated FA of physiological & nutritional
significance

14. Unsaturated FA of significance

15. Few properties of FA
• Melting point: The short and medium chain
FA are liquids, whereas the long chain FA are
solids at 250 C
• The melting and boiling points increase, with
increase in chain length
• The unsaturated FA have lower melting
points compared to saturated FA with the
same chain length
• Unsaturation decreases the melting points of
FA

16. Few properties of FA contd
• Lipid peroxidation: In vitro, lipid peroxidation
leads to rancidity (unpleasant smell).
• In vivo, the membrane lipids are more liable
to attack by free radicals and damage the
membrane, causing cancer, inflammatory
diseases, atherosclerosis or aging.
• Lipid antioxidant prevent the lipid peroxidation
• Vitamin E is an important antioxidant in the
human body
- C = C-O
– O peroxide

17. B.Phospholipids (PL)
• Phospholipids are the main lipid constituents of
membranes.
• Take part in lipoprotein metabolism
• PL are derivatives of phosphatidic acid.
• The phosphate is esterified with the –OH of a
suitable alcohol (glycerol).

18. PL contd….
1. Phosphatidyl choline (lecithin).
• Lecithin is phosphoacylglycerol containing
choline and represent body’s store of
choline.
• Choline is important in nerve transmission
as acetylcholine and serves as surfactant.

19. 2.Phosphatidyl ethanolamine and
3.Phosphatidyl serine
• Phosphatidyl ethanolamine
(cephaline) and
Phosphatidyl serine found
in most tissue differ from
lecithin only in that
ethanolamine or serine
replaces choline

20. 4.Phosphatidyl inositol
• Phosphatidyl inositol is
a precursor of second
messengers
• Phosphatidyl inositol
4,5 bisphosphate is a
constituent of cell
membrane
• Upon stimulation by an
hormone it is cleaved
into diacylglycerol and
inositol triphosphate
IP3.

21. 5.Cardiolipin
• Cardiolipin is a major lipid of mitochondrial
membrane.
• It is composed of two phosphatidic acids
(diphosphatidylglycerol)

22. 6.Plasmalogen
• Plasmalogen occurs in brain and muscle
• Resemble Phosphatidyl ethanolamine but
posses an ether link on carbon 1 instead of ester
link found in acylglycerols

23. 7.Sphingomyelins
• Sphingomyelins are found in nervous tissue and
brain
• Consists of FA, phosphoric acid, choline and
complex amino alcohol, sphingosine
• No glycerol is present
• Sphingosine with FA is known as ceramide

24. C.Glycolipids
• Glycolipids are made
up of lipids and
carbohydrates.
• They are widely
present in the body,
particularly in brain
• They provide the outer
layer of membranes
• Galactosyl ceramide is
shown in the figure
• Gangliosides are
glycosphingolipids
containing one or more
sialic acid. N acetyl
neuraminic acid is the
main sialic acid.
(NANA).

25. Structure of Gangliosides (GM2)

26. D.Steroids
• Precursors for many important steroids
such as, bile acids, adrenocortical
hormones, sex hormones and D vitamins
• All the steroids have a similar cyclic
nucleus resembling phenanthrene (rings
A,B, & C) to which a cyclopentane ring D
is attached. The carbon positions are
numbered as shown in the figure.
• Cholesterol is the best known steroid,
because of its association with
atherosclerosis (thickening of blood
vessels supplying the heart)

27. Steroids contd…
• If a compound has
one or more hydroxyl
groups and no
carbonyl or carboxyl
groups, it is called a
sterol and the name
ends as ‘ol’. Eg.,
cholesterol and
ergosterol
(Precursor of D
vitamin)

28. Eicosanoids
• These are compounds derived from eicosa
(20C) polyunsaturated arachidonic acid.
• They comprise:
1. Prostanoids:- prostaglandins (PGs),
prostacyclins (PGIs), Thromboxanes (TXs)
2. Leukotrienes (LTs)
3. Lipoxins (LXs)
• They are produced locally, have their action
locally and have short half life
• Their biologic actions are mediated by
plasma and nuclear membrane

29. Examples of eicosanoids

30. Lipids- Oil: water interface
• Fatty acids, phospholipids, sphingolipids,
bile salts and to lesser extent cholesterol
are amphipathic (have both polar &
nonpolar groups).
• They become orient at oil-water interface
with the polar groups at water phase and
non-polar groups at oil phase to form
membranes, micelles, liposomes and
emulsions.
• Phospholipids are the most common lipids
present in the membranes

31. Membrane / Micelle

32. Model of membrane structure