Lipids of physiologic significance following the curriculum of Medical Biochemistry for MBBS course

1. Dr. Farhana Atia
Assistant Professor
Department of Biochemistry
Nilphamari Medical College, Nilphamari
Bangladesh
Biomolecules: Lipids

2. Lipids
 Lipids are heterogeneous group of compounds
that are related more by their physical than by
their chemical properties
 They contain C, H, O ± P, N & S
 They have common properties of being
1. Insoluble in water
2. Soluble in nonpolar solvents as ether and
benzene
3. Associated with fatty acids and utilized by
living organisms

3. Biomedical Importance
 Major source of energy for the body (High caloric value=
9.3 Kcal/g)
 Important dietary constituent, fat soluble vitamins &
essential fatty acid are contained in the fat of natural
food
 Fat is stored in adipose tissue
 Serve as thermal insulator in subcutaneous tissues &
around certain organs
 Act as electrical insulator, allowing rapid propagation of
depolarization waves along myelinated nerves
 Combination of lipid & protein (LP) serve as the means
of transporting lipid in blood

4. Biomedical importance
 Provide hydrophobic barrier that permits partitioning of
the aqueous contents of cells & subcutaneous
structures
 Some fat soluble vitamins have regulatory or coenzyme
function
 Prostaglandins & steroid hormones play a major roles in
the control of the body’s homeostasis
 Have essential role in nutrition & health
Imbalance of lipid metabolism may lead to some major
clinical problems
Atherosclerosis
Obesity
Diabetes Mellitus

5. Lipids: Classification
1. Simple lipid: Esters of FA with various alcohol
 Fat: Esters of FA with glycerol. [Oil- in liquid state]
 Waxes: Esters of FA with HMW monohydric alcohol
2. Complex lipid: Containing groups in addition to
alcohol & FA
(1) Phospholipids: Containing a phosphoric acid
residue
 Glycerophospholipid [alcohol- glycerol]
 Sphingophospholipid [alcohol- sphigosine]
(2) Glycolipids (glycosphingolipid): Contain FA,
Sphingosine & carbohydrate
(3) Other: Sulpholipid, Aminolipid, Lipoproteins

6. Lipids: Classification
3. Derived lipid : Formed from hydrolysis of both
simple and complex lipids.
 Fatty acid
 Glycerol
 Steroids
 Other alcohol
 Fatty aldehyde
 Ketone body
 Hydrocarbon
 Lipid soluble vitamins
 Hormones

7. LIPID
S
Simple
FATS
WAXES
Complex
GLYCO
LIPIDS
PHOSPHO
LIPIDS
GlyceroPL
SphingoPL
Other CL
DERIVED
HYDROLYSI
S OF
COMPOUND
LIPIDS
F.As
ALCOHOLS
ASSOCIATED
WITH LIPIDS
STEROIDS
FAT SOLUBLE
VITAMINS

8. Fatty acids
(Aliphatic carboxylic acid)
 Long hydrocarbon chain with a polar carboxyl group
at its end.
 Amphipathic molecule
Polar / hydrophilic: COO⁻
Nonpolar / hydrophobic: Long HC chain
 Present in body
Mainly as esters in natural fat & oils
Unesterified/ FFA [transported in plasma]
 Natural FA: usually even number of C atom (14-24)

9. Fatty acids: Nomenclature
 FAs are named after corresponding hydrocarbon
 Numbering of C atom
• From carboxyl carbon (no. 1) - 2, 3, 4 α, β, γ
• Terminal methyl carbon- ω / n
 Number & position of double bond
• ∆⁹: between 9/10 C
• ω9: On 9th counting from ω C
• 3 series of FA family: ω9, ω6, ω3

10. Fatty Acids: Classification
1. Saturated FA: No double bonds
 Palmitic acid (16C), Stearic acid (18C), Lauric
acid (12C)
 Source: Animal & plant fat, coconut oil, butter,
nutmeg, cinnamon, palm kernel, waxes
2. Unsaturated FA : One or more double bonds
3. Eicosanoids : Derived from eicosa (20-carbon)
polyenoic fatty acid.

11. Unsaturated Fatty acids
1. Monounsaturated FA: one double bond.
• Oleic acid (18:1;9)
• Source: nearly all fats, high in olive oil
2. Polyunsaturated FA (PUFA): 2/more double bonds.
• Linoleic (18:2;9,2)
• α-Linolenic (18:3;9,12,15)
• Arachidonic (20:4;5,8,11,14)
• Cervonic (22:6;4,7,10,13,16,19)
• Source: Corn, peanut, cotton seed, soy bean,
linseed oil, Fish oil (cod liver, salmon oil),
phospholipids in brain

12. Fatty Acids: Classification
Eicosanoids: Comprises-
 Prostanoides
Prostaglandins/ PGs
Prostacyclins/ PGIs
Thromboxanes/ TXs
 Leukotreins/ LTs
 Lipoxins/ LXs
PGs exist in all mammalian
tissue
Synthesized in vivo
According to Chain length
fatty acids are-
Short chain FA: 2-10
carbon.
Acetic acid (2C), butyric
acid (4C)
Long chain FA: >10
carbon.
Palmitic (16C), stearic
(18C)

13. Essential fatty acids
 Polyunsaturated fatty acids
 Human body is unable to synthesize
 Must be supplied in diet
 Linoleic acid, ω₆ FA , ( AA  Prostaglandins)
 α-Linolenic acid, ω₃ FA (Important for growth &
development)
 Arachidonic acid, (ω₆ FA), become essential if
linoleic acid is absent in diet

14. Essential fatty acids
 Maintain fluidity of membrane structure
 Deficiency rare, occur in
• Infant on formula diet
• On IV nutrition exclusively for long time
 Result in
• Scaly dermatitis (icthyosis)
• Hair loss
• Visual abnormality
• Neurologic abnormality
• Poor wound healing

15. ω₆/n₆ Family
 From vegetable oil: nuts,
avocado, olive, soy bean,
sesame, cotton seed, corn
 ↓plasma cholesterol
 ↓ LDL, also ↓HDL
 Excess intake (↑PUFA)
oxidation of FA ↑free
radicals
Cancer
Inflammatory Disease
Atherosclerosis
Aging
ω₃ / n₃ Family
 From plants: linseed oil
 Fish oil (DHA & EPA)
 Have anti-inflammatory
effect. So beneficial in
 cardiovascular disease
 Cancer
 Rheumatoid arthritis
 Alzheimer disease
 In infant- helps in brain
development

16. Eicosanoids
 Prostaglandins & related compounds, thromboxanes &
leukotriens are collectively known as eicosanoids
 Origin: PUFA with 20C
 Extremely potent compounds, elicit a wide range of
responses
• Physiologic [inflammatory]
• Pathologic [hypersensitivity]
 Functionally compared to hormone, but
 Produce in small amount in all tissue
 Act locally
 Not stored, extremely short half life
 Action mediated by plasma mem. G protein coupled receptor

17. Synthesis of eicosanoids
Diet (EFA)Linoleic acid Arachidonic acid
Incorporated into membrane bound PL
LXs
PGE₂

18. Functions of Eicosanoids
PGF₂α
 Produce by- most tissue
 Vasoconstriction
 Contraction of smooth
muscle
 Uterine contraction
PGE₂
 Produced-most tissue, kidney
 Vasodilatation
 Relax smooth muscle
 Used to induce labour
PGI₂
 Produced in endothelium
 Vasodilatation
 Inhibit platelet aggregation
TXA₂
 Produced by platelets
 Promote platelet
aggregation
 Vasoconstriction
 Mobilize IC calcium
 Contraction of smooth
muscle

19. LTA₄
 Produce- leukocytes, platelets,
mast cell, heart & lung vascular
tissue
LTC₄/ LTD₄/ LTE₄
 Contraction of smooth muscle
 Broncho-constriction
 Vasoconstriction
 ↑vascular permeability
 Make up slow reacting
substances [SRS] of anaphylaxis
 Involved in pathophysiology of
asthma
LTB₄
 ↑ chemotaxis of
PMN leukocytes
 Release of lysosomal
enzyme
 Adhesion of WBC
LXs
 Anti-inflammatory
role
 Immuno-regulatory
function

20. Triacylglycerol
 Esters of trihydric
alcohol and fatty acids
 Glycerol : Alcohol with
3 OH groups
 Main storage forms of
fatty acids
 Thermal insulator

21. Phospholipids
 Esters of fatty acids, which contain an alcohol &
one or more fatty acids and a phosphoric acid
residue.
 They frequently have nitrogen containing bases
(choline) & other substituents
 Glycerophospholipid
[alcohol- glycerol]
 Sphingophospholipid
[alcohol- sphigosine]

22. Glycerophospholipids Sphingophospholipids
 Phosphatidylcholine (lecithin)
 Most abundant PL in membrane
 Acetylcholine
 Dipalmitoyl lecithin (surfactant)
 Phosphatidyl ethanolamine
(cephalin)
 Phosphatidyl serine
 Phosphatidyl inositol (2nd
messenger)
 Plasmalogens (Brain, heart)
 Cardiolipins (mitochondria)
 Spingomyelins
 Component of cell
membrane, nervous
tissue and myelin
sheath
 Play role in cell
signaling & apoptosis
 Ceramide:
combination of
sphingosine plus fatty
acid

23. Biomedical Importance of Phospholipids
 They are main lipid constituents of cell membrane
 Provide arachidonic acid for eicosanoids
 Surfactant- prevent adherence of inner surface of lung
 Play an important part in cell signaling & membrane
trafficking
 Keep cholesterol in solution (in bile)
 Play role in apoptosis (programmed cell death)
 Acetylcholine is important in nervous transmission
 Cardiolipin- decrease level cause heart failure,
hypothyroidism
 Plasmalogens may have a protective effect against reactive
oxygen species

24. Glycolipids
 Glycosphingolipids
 Contain a fatty acid, sphingosine, and carbohydrate
 Widely distributed in every tissue (particularly in brain)
 Example: Cerebrosides, Gangliosides
Biomedical Importance
 Component of biological membrane
 Present in brain, other nervous tissue & myelin
 Cell surface receptor (glycocalyx)
 Cellular communication, cell-cell recognition
 Receptors for hormone & bacterial toxins (cholera toxin)

25. Steroids
 Derived lipid
 Complex molecule consisting of four
fused carbon ring (17C)
 Phenanthrene nucleus: Three 6-
carbon ring (A,B, C)
 Cyclopentane: D ring
 10, 13: methyl; 17: side chain
 Common cyclic ring called “steroid
nucleus”/
cyclopentanoperhydrophenanthrene
ring

26.  Important steroids include
A. Bile acids and salts
B. Adrenocortical hormones
C. Sex hormones
D. Vitamin D
E. Cardiac glycosides
Steroids
Bile salt

27. Sterols
 If the steroid has 1/ more OH groups & no
carbonyl/ carboxyl group, it is a sterol. The name
terminates in –ol.
 Cholesterol, ergosterol, sitosterol, coprosterol
 Cholesterol : Major sterol in animal tissue
 3: OH; 17: Aliphatic side
 Ergosterol: In plant & yeast, precursor of vitamin D

28. Cholesterol
 Cholesterol is the major sterol in animal tissues.
 Body cholesterol-
 50% Synthesized in body (700 mg/d)
 50% from Diet
 70 kg man: 140 gm cholesterol
 Source:
 Egg yolk
 Meat
 Liver
 Brain
 [No vegetable oil contains any cholesterol]

29. Biomedical importance
 Cholesterol is widely distributed in all cells of the body
but particularly in nervous tissue
 It is an amphipathic lipid & is an essential structural
component of cell membrane. It is important for the
maintenance of correct permeability & fluidity
 Major constituent of plasma lipoprotein
 Present in tissue & plasma as free/ combined with a
LCFA as cholesteryl ester (storage form)
 Occurs in animal but not in plants or bacteria
 Precursor of all steroids in body including
corticosteroids, sex hormones, bile acids, vitamin D

30.  Plasma LDL is the vehicle that supplies cholesterol &
cholesteryl ester to many tissues
 Free cholesterol is removed from the tissues by
plasma HDL & transported to liver.
It is eliminated from the body either unchanged or
after conversion of bile acids (reverse cholesterol
transport)
 Cholesterol is a major constituent of gall stone
 Chief factor in the genesis of atherosclerosis and
heart disease
Biomedical importance

31. Thank You