This lecture file is meant for students pursuing MBBS, BDS, Nursing and/or higher education in Biochemistry.

1. “You are what you eat !”
Thursday, June 9, 2016
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Rajesh Chaudhary

2. Department of Biochemistry, NGMC, ChisapaniThursday, June 9,
2016
Rajesh Chaudhary 2

3. Biomedical importance and function
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 Phospholipids and Sterols are major structural elements of
cell membrane.
 Role as enzyme cofactor.
 Electron carrier.
 Light-absorbing pigment.
 Hydrophobic-anchor for proteins.
 Emulsifying agent in digestive tract.

4. Categories of biological lipids
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Eight major categories of Biological lipids

5. Lipids Vs. Fatty acids Vs.
Triacylglycerol
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 Simplest lipid constructed from Fatty
acids are Triacylglycerol, also
referred to as TG, Fat or Neutral
fat.
How are ester link formed?

6. Triacylglycerol (TG)
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 Examples of simple TG: Tripalmitin,
Tristearin, Triolein.
Types of Triacylglycerols
Simple Complex

7. Triacylglycerol (TG)
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1. Triglycerides as storage
form of energy in
Eukaryotes and higher
vertebrates
2. Role of Lipases

8. Triacylglycerol (TG)
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 What is the advantage of having TG as a stored
fuel rather than polysaccharide such as Glycogen
and Starch?
 1. The carbon atom of fatty acid are more reduced
than glycogen and starch, thus, gives more energy.
 (A gram for gram)
 2. TG are hydrophobic thus unhydrated. Therefore,
organisms don’t have to carry extra weight of water.

9. Classification of Lipids
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 1. Simple lipids
 Examples: Fats and Waxes.
 2. Complex lipids
 Examples: Phospholipids (glycerophospholipids, sphingophospholipids)
 Glycolipids: glycosphingolipids
 3. Precursor and derived lipids
 Examples: fatty acid, glycerol, steroids, fatty aldehydes, ketone
bodies.
Simple lipids Complex lipids

10. Classification of Lipids
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 Fatty acids are aliphatic carboxylic acid.
 Are either: 1. Saturated and 2. Unsaturated
 1. Saturated: doesn’t contain double bond
 2. Unsaturated: contains double bond
2. Unsaturated
 2.1. Monounsaturated (E.g.: Oleic acid)
 2.2. Polyunsaturated (E.g.: polyethenoid, polyenoic acids)
 2.3. Eicosanoids (E.g.: Prostanoids, Lipoxin and Leukotrienes)

11. Nomenclature
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 Saturated acids ends in “-anoic” acid.
 Example: Octanoic acid
 Unsaturated acids with double bonds end in
“-enoic” acid.
 Example: Octadecenoic acid

12. Examples of saturated, monounsaturated
and polyunsaturated fatty acids
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Mono unsaturated fatty acid (Oleic acid, C18:1)
A saturated fatty acid (Palmitic acid, C16)
A polyunsaturated fatty acid (Linoleic acid, C18:2)

13. Basic rules of nomenclature in Lipids
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 1. Carbon atoms are named from the carboxyl carbon. (Carbon No.
1)
 2. The rest of the carbon following are named as: 2,3,4… and so on
– also known as “a”, “b”, “g” and so on….
 3. For polyunsaturated fatty acids: The no. of carbon is named
from the opposite side of the carboxyl carbon and given the no.
(Carbon No. 1) – and called “omega (w)”.
 Delta (D) is used for indicating the position and number of
double bonds.

14. Nomenclature
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Fatty acids are hydrocarbon derivatives (Length: C4 to C36).

15. Monounsaturated fatty acids
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 … acids containing one double bond.
Figure. Oleic acid. n-9 is equivalent to w9.

16. Examples
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 Palmitic acid: abbreviated form  16:0
 Oleic acid: 18:1
 Most commonly occurring fatty acids have even
no. of carbon chain  12 – 24.

17. Common pattern of location of
double bonds in Fatty acids
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 In most monounsaturated fatty acids, double bond is
between C9 and C10. (D9)
 Other double bonds of polyunsaturated fatty acids
(PUFA) are at D12 and D15.
 Exception: Arachidonic acid
 In most naturally occurring PUFA have cis-configuration.
 Trans-FA are produced by fermentation in rumen of
ruminants.

18. Key convention on Polyunsaturated
Fatty Acids (PUFA)
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 Double bond between the 3rd. And 4th. Carbon atom
from methyl end is of special importance in human
nutrition.
 Alternative nomenclature is used for PUFA rather than
conventional one.
 1. Carbon atom to the most distant site from the carboxylic
terminal gets the name “w” – the carbon no. 1.
 Example: Omega-3 fatty acid.

19. Key convention in PUFAS
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 Example: Omega-3 PUFA (a-linolenic acid)
(ALA; 18:3(D9,12,15))
(EPA; 20:5(D5,8,11,14,17) (DHA; 22:6(D4,7,10,13,16,19)
An imbalance in
𝑂𝑚𝑒𝑔𝑎−6 𝑓𝑎𝑡𝑡𝑦 𝑎𝑐𝑖𝑑
𝑂𝑚𝑒𝑔𝑎−3 𝑓𝑎𝑡𝑡𝑦 𝑎𝑐𝑖𝑑
 Cardiovascular diseases
Optimal ratio is 1:1 to 4:1, but North American diet contains
10:1 or 30:1.

20. Key convention in PUFA
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 The length and degree of
unsaturation affects the
melting point of
unsaturated fatty acids.
 The most stable
conformation is the fully
extended form.

21. Geometric isomerism of D9, 18:1 fatty
acids (Oleic and Elaidic acids)
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 Effect of temperature on
structure of lipids (Higher Vs.
Lower)?
 Presence of acyl chains on
same side vs opposite side
around carbon containing
double bond
Arachidonic acid

22. Physical and Physiologic properties
of Fatty acids
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 Melting point of even numbered carbon fatty acids
increase with chain length and decrease according
to unsaturation.
 Triacylglycerol containing three saturated fatty acids
of 12 carbons or more Vs. if, fatty acid residues
are 18:2.
 Membrane lipids are liquid at room temperature.

23. Structural Lipids in Membranes
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 What are the structural lipids in membrane?
 1. Glycerophospholipids (2 fatty acids + glycerol) –
hydrophobic region
 2. Galactolipids & Sulfolipids (2 fatty acids + 1 glycerol) but
lacks Phosphate
 3. Archael tetraether lipids (2 alkyl long chain + ether-linked to
glycerol @ both ends)
 4. Sphingolipids (1 fatty acids + fatty amine (Sphingosine))
 5. Sterol

24. Phospholipids Vs. Glycolipids
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 In Glycerophospolipids and some Sphingolipids, a
polar head group is joined to hydrophobic moiety
with phosphodiester linkage – these are called
“Phospholipids”.
 But, some Sphingolipids lacks “Phosphate” group
but can be simple sugar or complex oligosaccharides
at their polar end – known as “Glycolipids”.

25. Some common types of storage and
membrane lipids
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26. Glycerophospholipids
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1. The fatty acids in the “glycerophospholipids” can be any of wide variety.
2. Distribution of molecular species is specific for different organisms, different
tissues of the same organism, and different glycerophospholipids in the same
cell or tissue.
3. In general, glycerophospholipids contain C16 or C18 @ C-1 and a C18 or
C20 @ C-2.

27. Glycerophospholipids
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 … called “Phosphoglycerides”.
 2 fatty acids + 1st. And 2nd. Carbon of glycerol.
 Glycerol is Prochiral.
 No asymmetric carbon atom.
 Some glycerophospholipids have ether-
linked fatty acids.

28. Glycerophospholipids
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1
2
… released from leukocyte called
“basophils” and stimulate platelet
aggregation and release of
serotonine (a vasoconstrictor)

29. Sphingolipids
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 … 4th. Large class of membrane lipids.
 … contains one polar head and two non-polar tails.
 Doesn’t contain “glycerol”.
 3 subclasses of Sphingolipids
 1. sphingomyelins
 2. neutral glycolipids
 3. and, gangliosides
Ceramide

30. Sphingolipids
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 Sphingolipids at cell surface are
sites of biological recognition.
 Many of these are specially
prominent in the plasma
membranes of neurons.
 Carbohydrate moieties of certain
sphingolipids define the human
blood groups.
NOTE: Phospholipids and Sphingolipids are
degraded in lysosomes.

31. Sterols
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 … structural lipids
present in the
membrane of most
eukaryotic cells.
 Cholesterol is one
major sterol.

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