Lipids are a diverse class of organic compounds that include fats, waxes, sterols, and fat-soluble vitamins. They are insoluble in water but soluble in organic solvents. Lipids serve important biological functions like energy storage, structural components of cell membranes, and signaling molecules. The main classes of lipids are fatty acids, triglycerides, phospholipids, sterols, and fat-soluble vitamins. Lipids are broken down and absorbed in the small intestine after digestion. They provide the most efficient form of stored energy in the body.

1. Definition
Classification
Biological Importance
Physiological Importance
S.M. KHALEDUR RAHMAN
Graduate student
Department of Biochemistry
Kagawa University School of Medicine
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2. Dietary sources of Lipids
 Animal Sources
Dairy products- Milk, butter, ghee
Meat and Fish, Pork, eggs
 Vegetable Sources
Cooking oils- Sunflower oil, Mustard oil,
Ground nut oil
Fats from other vegetable sources
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3. organic substances relatively insoluble in
water but soluble in organic solvents
like chloroform, ether and benzene
In 1815, Henri Braconnot classified lipids in two categories,
suifs (solid fats or tallow) and huiles (fluid oils). In 1823,
Michel Chevreul developed a more detailed classification,
including oils, fats, tallow, waxes, resins, balsams and volatile
oils (or essential oils)
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4. Lipids
•Like carbohydrate, lipids are composed of carbon,
hydrogen and oxygen
•Unlike carbohydrate, they do not contain multiple
hydroxyl groups for hydrogen bonding, and
therefore are insoluble in water
• Lipids include a large variety of molecules:
- fatty acids
- triglycerides
- waxes
- eicosanoids
- steroids
- fat soluble vitamins 4

5. • Insoluble in water
•Wide range of functions: insulate and protect
internal organs, signaling molecules, energy
• Most efficient form in which energy is stored in the
body
•Excess glucose, lipids and proteins are stored in
adipose cells
General info on Lipids…
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6. Simple lipids
Complex lipids
Derived lipids
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7. They are esters of fatty acids with various alcohols
Neutral fats or Oils
Alcohol is
GLYCEROL
Waxes
Alcohol other
than glycerol
H2C OH
HC OH
H2C OH
glycerol
• Also called
‘Glycerin’
• Trihydric alcohol
as it contains
three hydroxyl
groups
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8. Esters of Fatty acidswith
the alcohol GLYCEROL
Uncharged
Triglyceride (Neutral fat)
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9. Esters of Fatty acids
with higher molecular
weight monohydric
alcohols
EXAMPLES
 Lanolin
 Bees wax
 Palm wax
 Sperm whale oil
 Synthetic spermaceti
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10. Lipids: diverse class of molecules
1)Energy and storage – fatty acids,
triacyl-glycerides, waxes
2)Membrane structure –
phospholipids, glycolipids, sterols
3)Signaling, cofactors and pigments –
Eicosanoids, sterols, fat soluble vitamins
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11. Energy & storage Lipids
• Fatty Acids
• Triacylgerols
• Waxes
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12. •Long chain, even number carboxylic acids, typically
between 12 and 26 carbons
•Insoluble in water
•Some contain double bonds
 Saturated fatty acids have no double bonds
 Unsaturated fatty acids have at least one double
bond
Fatty Acids
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13. Properties of Saturated
Fatty Acids
 Contain only single C–C bonds
 Closely packed
 Strong attractions between chains
 High melting points
 Solids at room temperature
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14. Properties of Unsaturated
Fatty Acids
 Contain one or more double C=C bonds
 Nonlinear chains do not allow molecules
to pack closely
 Few interactions between chains
 Low melting points
 Liquids at room temperature
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15. Common Fatty Acids
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16. Subclassified according to the type of prosthetic
group
Phospholipids Glycolipids Lipoproteins
These are esters of fatty acids with alcohol
containing additional prosthetic groups
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17. They
frequently
have nitrogen
containing
bases
contain an alcohol, two fatty
acids, and a phosphate ester.
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18. Phospholipids
may be
classified on
the basis of the
type of alcohol
present
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19. Sphingolipids
Some involved in
signal transduction
& cell surface
recognition
One fatty acid joined
to sphingosine
Examples:
Sphingomyelin
Glycosphingolipids
Gangliosides
Sphingomyelin-
animal cells,
especially myelin
• Polar or charged group is
attached to the third
carbon of glycerol
– Basis for
nomenclature
• Most abundant lipid in
biological membranes
Glycerophospholipids
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20. Glycerophospholipids Sphingophospholipids
 Phosphatidylcholine
 Phosphatidyl
ethanolamine
 Phosphatidyl serine
 Phosphatidyl inositol
 Plasmalogens
 Cardiolipins
 Sphingomyelins
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21. • Functions
Components of cell membrane, mitochondrial membrane and
lipoproteins
Participate in lipid absorption and transportation from intestine
Play important role in blood coagulation
 Required for enzyme reaction- especially in mitochondrial electron
transport chain
Act as reservoir of second messenger- Phosphatidyl Inositol
Act as cofactor for the activity of Lipoprotein lipase
Phospholipids of myelin sheath provide insulation around the nerve
fibers
Dipalmitoyl lecithin acts as a surfactant
Food sources : Egg yolks, liver, soybeans, peanuts
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22. Membranes
• Complex lipids form the membranes around
cells and small structures within cells.
• In aqueous solution, complex lipids spontaneously
form into a lipid bilayer, with a back-to-back
arrangement of lipid monolayers.
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 Polar (hydrophilic) head groups are in
contact with the aqueous environment.
 Nonpolar (hydrophobic) tails are buried
within the bilayer
 The arrangement of hydrocarbon tails in
the interior can be rigid (if rich in
saturated fatty acids) or fluid (if rich in
unsaturated fatty acids).

23. Lipids in Membranes: Fluid Mosaic Model
Polar heads and nonpolar tails
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24. FATTYACID + ALCOHOL[SPINGOSINE] +
CARBOHYDRATE WITH NITROGEN BASE
Examples
Cerebrosides
Gangliosides
Complex lipids that contain a carbohydrate
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25. Chylomicrons
Very low-density lipoprotein (VLDL)
Low density lipoprotein (LDL)
High density lipoprotein (HDL)
Lipid with
prosthetic
group
PROTEIN
A lipoprotein is a biochemical assembly
whose primary purpose is to transport
hydrophobic lipid (also known as fat)
molecules in water, as in blood plasma or
other extracellular fluids.
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26. Lipoproteins
Cholesterol, along with fats, are transported by lipoproteins
VLDL (very low-density lipoproteins)- transport
triglycerides
LDL (low-density lipoproteins)- transport cholesterol
from liver to tissues
HDL (high-density lipoproteins)- transport cholesterol
from tissues to the liver for elimination
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27. Lipoproteins
Schematic presentation of a low-density lipoprotein
They have a single-layer
phospholipid and
cholesterol outer shell,
with the hydrophilic
portions oriented outward
toward the surrounding
water and lipophilic
portions oriented inward
toward the lipid's
molecules within the
particles. 27

28. Examples
Fatty acids Steroids Cholesterol VitaminA
and D
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29. Essential Fatty Acids (EFA)
• Omega-3:
– Eicosapentaenoic acid(EPA)
– Docosahexaenoic acid(DHA)
–Alpha-linolenic acid (ALA)
• flaxseed--most, canola (rapeseed), soybean,
walnut, wheat germ
• body can make some EPA and DHA from ALA
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30. Omega-3 Fatty Acids
• Associated with:
– anti-inflammatory, antithrombotic,
antiarrhythmic, hypolipidemic, vasodilatory
properties
• Inflammatory conditions
• Ulcerative colitis, Cardiovascular disease
 Type 2 diabetes
 Renal disease
 Mental function
 Growth and development
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31. Essential Fatty Acid Deficiency
• Classical symptoms include:
– growth retardation, reproductive failure, skin lesions,
kidney and liver disorders, neurological and visual
problems
• People with chronic intestinal diseases
• Depression caused by omega-3 deficiency
– inadequate intake alters brain activity
• Attention Deficit Hyperactivity Disorder
– lower levels of omega-3 causes more behavioral
problems
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32. Steroids
A group of plant and
animal lipids that have
this tetracyclic ring
structure.
•cholesterol, bile acids,
vitamin D, and many
hormones
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33. Cholesterol
Cholesterol is the major sterol in animal tissues
• Synthesis
– Made mainly in the liver
• Food sources
– Found only in animal foods
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34. Cholesterol is the most abundant steroid in the human
body, and the most important one.
 It is a component in plasma membranes in all
animal cells.
 It is the precursor of all steroid hormones and bile acids.
 Major factor in the development of atherosclerosis
 Transported by lipoproteins
Cholesterol
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35. Bile Salts
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Bile salts, the oxidation products of cholesterol.
Synthesized in the liver, stored in the
gallbladder, and secreted into the intestine
where they emulsify dietary fats and aid in
their absorption and digestion

36. --derivatives of 20-carbon fatty acids
--affect cells where they are made
--have different effects in different cells
--cause muscles to contract and relax
--helps in regulating blood pressure, blood clot formation
and immune response
--participate in immune response to injury and infection,
producing fever, inflammation, and pain
--include; prostaglandins, thromboxanes,
leukotrienes
"Eicosanoid" is derived from a Greek word
“eicosa” meaning "twenty”
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37. Prostaglandins & Leukotriene
They are not stored in tissues as such but are
synthesized from membrane-bound 20-carbon
polyunsaturated fatty acids, in response to specific
physiological triggers.
One such polyunsaturated fatty acid is arachidonic acid
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38. Triglycerides
• Structure
– Glycerol + 3 fatty acids
• Functions
– Energy source
• 9 kcals per gram
• Form of stored energy in
adipose tissue
– Insulation and protection
– Carrier of fat-soluble vitamins
– Sensory properties in food
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39. Triglycerides
Food sources
– Fats and oils
• butter, margarine, meat, baked goods,
snack foods, salad dressings, dairy
products, nuts, seeds
– Sources of omega-3 fatty acids
• Soybean, canola, walnut, flaxseed oils
• Salmon, tuna, mackerel
– Sources of omega-6 fatty acids
• Vegetable oils
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40. Triacylglycerols: stored fat
• Insulation - seals, penguins
• Energy– Hibernation
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41. Lipid Digestion
• In the Mouth
– hard fats begin to melt; lingual lipase
• In the Stomach
– gastric lipase breaks into Single Chain Fatty
Acids
• In the Small Intestine
– release of Cholecystokinin; bile-emulsifier; fat
drawn into surrounding watery fluids; then
intestinal lipases removes each triglyceride
fatty acid and leave glycerol
• Bile Routes
– reabsorbed or trapped by dietary fiber
Recommended 30% of
daily diet
-10% monounsaturated
-10% saturated
-10% polyunsaturated
Most efficient form in
which energy is stored in
the body: 9 kcal/ gram as
opposed to carbohydrate
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42. 42

43. Precursor of many steroid hormones, vitamin D
Bile acids help in absorption of fat soluble vitamins
Fats serve as surfactants by reducing surface tension
Improve food taste and medication palatability
Lipoproteins serve to transport lipids
Storage form of energy
Structural component of cell membrane
Act as thermal insulator
Protection of internal organs
Act as electric insulators in neurons
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44. Sleep Induction
Lipids in Physiology
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45. 45

46. Function as antibacterial
Soap making. Deodorants, foundation creams,
hand lotions, hair straightening products, and
shaving creams.
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47. 1. What is a polyunsaturated fatty acid?
2. What are the properties of unsaturated FA?
3. What are the functions of lipoproteins?
4. What molecules react to form a triglyceride?
5. How lipid molecules are digested?
6. What are the major functions of lipids? HOMEW
ORK
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48. THANKS TO ALL
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