Lipid chemistry question bank

1. Question bank
LIPID CHEMISTRY

2. Question 1
• Name the essential fatty acids
• (EFAs), linoleic acid (LA), and alpha-linolenic acid

3. Question 2
• Why arachidonic acid is not considered purely an essential fatty acid?
• Arachidonic acid is the precursor of prostaglandins.
• Arachidonic acid can be synthesized in the body, from linoleic acid, if
the latter is supplied in the diet.

4. Question 3
• What are the products of arachidonic acid?
• The arachidonic acid is rapidly converted into active metabolites
by cyclooxygenases to produce prostaglandins, prostacyclin
and thromboxanes, and by lipoxygenase to produce
leukotrienes

5. Question 4
• Prostaglandins and their importance

6. Question 5
• Iodine number and its importance
• Iodine number of a fat is defined as the number of grams of iodine
taken up by 100 grams of fat.
• It is an index of the degree of unsaturation and is directly
proportional to the content of unsaturated fatty acids.
• Higher the iodine number, higher is the degree of unsaturation, e.g.
iodine number of butter is 28, and that of sunflower oil is 130

7. Question6
• What is saponification number and iodine number? Write its
importance
• Saponification i. When triacylglycerols are hydrolyzed by alkali, the
process is known as saponification. The products are glycerol and
soaps
• ii. Saponification number is defined as the number of milligrams of
potassium hydroxide required to saponify one gram of fat.
• iii. It is an indication of the molecular weight of the fat, and is
inversely proportional to it.

8. Question 7
• Amphipathic lipids
• Phospholipids in general are amphipathic, particularly Lecithin.
• They have both hydro phobic and hydrophilic portion in their
molecule .
• The glycerol along with the phosphoric acid and choline constitute
the polar ‘head' of a phospholipid molecule, whereas the
hydrocarbon chains of the fatty acids represent the non polar ‘tail'.

9. Question 8
• Component and functions of phospholipids
• Phosphatidates i. These are derivatives of phosphatidic acid, which is
the simplest phospholipid.
• ii. Phosphatidic acid is made up of one glycerol to which two fatty acid
residues are esterified to carbon atoms 1 and 2. The 3rd hydroxyl
group is esterified to a phosphoric acid
• iii. The molecule has an asymmetric carbon atom and therefore,
exhibits optical isomerism.

10. • L-isomer is found in nature. Amphipathic Nature Phospholipids in
general are amphipathic, particularly Lecithin. They have both hydro
phobic and hydrophilic portion in their molecule ‘
• The glycerol along with the phosphoric acid and choline constitute
the polar ‘head' of a phospholipid molecule, whereas the
hydrocarbon chains of the fatty acids represent the non polar ‘tail'.

11. • When phospholipids are distributed in water, their hydrophobic parts
keep away from water, forming molecular aggregates called micelle .
• These are involved in solubilization of lipids in aqueous media and
help in digestion and absorption of lipids.
• Liposomes A lipid bilayer will close on itself under appropriate
conditions to form liposomes.

12. • Unilamellar or multilamellar liposomes may be formed. They may be
prepared by sonication of mixtures of phospholipids and cholesterol .
• Liposomes are microscopic spherical vesicles. When mixed in water
under special conditions, the phospholipids arrange themselves to
form a bilayer membrane which encloses some of the water in a
phospholipid sphere

13. • Drugs, proteins, enzymes, genes, etc. may be encapsulated by the
liposomes which could act as carriers for these substances to target
organs.
• Liposome-entrapped drugs exhibit superior pharmacological
properties than those observed with conventional formulations.
• Liposomes have important applications in cancer chemotherapy,
antimicrobial therapy, gene therapy, vaccines and diagnostic imaging

14. • Aquasomes They are one of the most recently developed delivery systems
that are making a niche as the peptide/protein carriers.
• These are nanoparticulate carrier systems with three layered self-
assembled structures.
• They comprise the central solid nanocrystalline core coated with
polyhydroxy oligomers onto which biochemically active molecules are
adsorbed.
• The solid core provides the structural stability. The carbohydrate coating
stabilizes the biochemically active molecules.
• As the conformational integrity of bioactive molecules is maintained,
aquasomes are being proposed as a carrier system for delivery of peptide
based pharmaceuticals

15. • . The delivery system has been successfully utilized for the delivery of
insulin, hemoglobin and various antigens. Oral delivery of enzymes
like serratiopeptidase has also been achieved

17. Question 9
• Phospholipids
• They contain glycerol, fatty acids and a nitrogenous base.

18. Question 10
• Structure of lecithin
• Phosphatidylcholine or Lecithin i. This is a nitrogen containing
phospholipid. The word lecithin is derived from the Greek word,
lekithos = egg yolk.
• It contains glycerol. ii. The alpha and beta positions are esterified
with fatty acids.

19. • Usually, the fatty acid attached to the beta carbon, is a PUFA molecule
iii. The phosphoric acid is added to the third position, to form
phosphatidic acid.
• The phosphate group is esterified to the quaternary nitrogen base,
Choline .The molecules of lecithin exist as zwitterions (pl = 6.7).

22. Question 11
• Pulmonary surfactant –structure and clinical importance
• Respiratory Distress Syndrome (RDS) It is due to a defect in the
biosynthesis of dipalmitoyl lecithin (DPL), the main pulmonary
surfactant.
• Premature infants have a higher incidence of RDS because the
immature lungs do not synthesize enough DPL.

23. Question 12
• What is surfactant ?explain its importance in the body in health and
disease?
• The lung maturity is assessed by measuring the lecithin-
sphingomyelin (L/S) ratio, which is an index of the surfactant (surface
tension lowering complex) concentration in amniotic fluid. In late
pregnancy, the cells lining the fetal alveoli start synthesizing
dipalmitoyl-lecithin so that the concentration of lecithin increases,
whereas that of sphingomyelin remains constant. As a result, as the
fetal lung matures, the lecithin-sphingo myelin (L/S) ratio rises. An L/S
ratio of 2 is taken usually as a critical value

24. • Normal lung function depends on a constant supply of lung surfactants. It
is produced by epithelial cells.
• It decreases surface tension of the aqueous layer of lung and prevents
collapse of lung alveoli.
• Constituents of surfactants are dipalmitoyl lecithin, phosphatidyl glycerol,
cholesterol and surfactant proteins A, B and C.
• During fetal life, the lung synthesizes sphingomyelin before 28th week of
gestation.
• But as fetus matures, more lecithin is synthesized. The lecithin-
sphingomyelin (LS) ratio of amniotic fluid is an index of fetal maturity.

25. • A ratio of 2 indicates full lung maturity. Low surfactant level can lead
to respiratory distress syndrome (RDS), which is a common cause of
neonatal morbidity

26. Question 13
• Phosphatidyl inositol –importance
• Here, phosphatidic acid is esterified to inositol.
• Phosphatidyl inositol bisphosphate or PIP2 is present in
biomembranes.
• This compound plays a vital role in the mediation of hormone action
on biomembranes and acts as a second messenger

27. Question 14
• Cardiolipin
• It is formed by reaction between CDP diacylglycerol and glycerol-3-
phosphate.

28. Question 15
• Write about biological actions and clinical applications of
prostaglandins?
• Effects on CVS Prostacyclin or PGI2 is synthesized by the vascular
endothelium.
• Major effect is vasodilatation. It also inhibits platelet aggregation and
has a protective effect on vessel wall against deposition of platelets.
• But any injury to the vessel wall would inhibit PGI2 synthesis so that
platelet aggregation occurs to promote thrombus formation.

29. • Thromboxane (TXA2 ) is the main PG produced by platelets.
• The major effects are vasoconstriction and platelet aggregation.
Prostacyclin and thromboxane are opposing in activity

30. • Prostaglandins lower the blood pressure. Effects on Ovary and Uterus
The PGF2 stimulates the uterine muscles.
• Hence PGF2 may be used for medical termination of pregnancy. Yet
another use is in inducing labor and arresting postpartum
hemorrhage.
• PGs are involved in LH induced ovulation. In cattle, if PG is given,
luteolysis takes place and animal goes into estrus

31. • Better fertilization rate is achieved with timely artificial insemination.
• Effects on Respiratory Tract The PGF is a constrictor of bronchial
smooth muscle; but PGE is a potent bronchodilator. PGE series are
used in aerosols for relieving bronchospasm.
• Effects on Immunity and Inflammation The PGE2 and D2 produce
inflammation by increasing capillary permeability. Erythema and
wheal are produced at the site of injury.

32. • The anti -inflammatory effect of PG synthesis inhibitor (aspirin;
cortisol). Moreover, PGE2 reduces both T and B cell functions. PGE2 is
a sleep promoting substance.
• Effects on Gastrointestinal Tract PGs in general inhibit gastric
secretion and increase intestinal motility. The inhibitory effect on
gastric secretion is used therapeutically in treatment of acid peptic
disease.

33. • But diarrhea may be an unwanted side effect.
• Metabolic Effects
• The metabolic effects may be through the action of hormones by the
modulating effect on cAMP production. Prostaglandin E2 decreases
lipolysis, increases calcium mobilization from bone and glycogen
synthesis

34. • Leukotrienes (LTs) They are produced from arachidonic acid.
• LT B4 is produced in neutrophils; it is the most potent chemotactic agent
(factor attracting cells to the inflammatory site). The number 4 denotes
that there are 4 double bonds in the structure.
• The 12-lipo-oxygenase in platelets produces 12-HETE (hydroxy eicosa
tetra-enoic acid) and 15-lipo-oxygenase in eosinophils produce 15-HETE.
• The slow reacting substance of anaphylaxis (SRS-A) contains LTC4 , LTD4
and LTE4 .
• They cause smooth muscle contraction, constrict the bronchioles,
increase capillary permeability, activate leukocytes and produce
vasoconstriction.

35. • SRS is the mediator of hypersensitivity reactions such as asthma.
Incorporation of DGLA into membrane phospholipids competes with
the incorporation of arachidonate so that diets enriched in GLA result
in an alteration in the ratio of membrane arachidonate to DGLA.
• Release of membrane DGLA occurs through the action of PLA2 just as
for release of arachidonate.
• Once DGLA is released it will compete with arachidonate for COXs and
LOXs.
• The products of COX action on DGLA are series-1 prostaglandins
(PGE1 ) and thromboxanes (TXA1

36. • PGE1 and TXA1 are anti-inflammatory, they induce vasodilation, and
inhibit platelet aggregation.
• When DGLA is a substrate for 15-LOX the product is 15-hydroxyeicosa
trienoic acid (15-HETrE).
• 15-HETrE is a potent inhibitor of 5-LOX which is the enzyme
responsible for the conversion of arachidonic acid to LTB4 .

37. • LTB4 is a potent inflammatory molecule through its action on
neutrophils, thus, DGLA serves to inhibit inflammation via the
eicosanoid pathway as well.
• Lipoxins They are a group of compounds produced by leukocytes.
They are conjugated tetrenes.
• They are formed by sequential action of 5 and 15-lipo-oxygenase.
LXA4 is the most common variety .
• It is anti-inflammatory and decreases immune response

38. Question 16
• Importance of sphingomyelin
• Sphingomyelins are the only sphingolipid that contain phosphate and
have no sugar moiety.
• They are found in large quantities in nervous system. Different
sphingomyelins may be formed depending on the fatty acid attached.
Common fatty acids found are—lignoceric (24 C), nervonic (24 C, one
double bond) and cervonic (22 C, 6 double bonds) acids .

39. • Because of its amphipathic nature sphingomyelin can act as an
emulsifying agent and detergent.
• The relative proportion of lecithin and sphingomyelin is important in
biological fluids like bile, amniotic fluid, etc. Sphingomyelin combined
with fatty acid is called ceramide, which is a component of
glycosphingolipids.

40. • Antiphospholipid antibodies have been found to be present in blood
in patients with autoimmune diseases and in patients with
thrombotic episodes.
• In pregnancy, the presence of these antibodies can cause
complications like miscarriage, eclampsia and preterm labor.
• Here the antibodies are developed against membrane phospholipid,
cardiolipin

41. Question 17
• Structure of cholesterol and its importance in the body
• Cholesterol is essential to life, as it performs a number of important
functions 1.
• It is a structural component of cell membrane. 2. Cholesterol is the
precursor for the synthesis of all other steroids in the body.
• These include steroid hormones, vitamin D and bile acids.
• 3. It is an essential ingredient in the structure of lipoproteins in which
form the lipids in the body are transported.
• 4. Fatty acids are transported to liver as cholesteryl esters for
oxidation.

42. All steroids have
cyclopentanoperhydrophenanthren
e ring system .It is a fused ring
system made up of 3 cyclohexane
rings designated as A, B and C and a
cyclopentane ring D. The six-
membered rings are in a
phenanthrene arrangement.
2. Total 27 carbon atoms.
3. One hydroxyl group at third
position which is characteristic of all
sterols. The OH group is beta
oriented, projecting above the
plane of ring.
4. Double bond between carbon
atoms 5 and 6.
5. An eight carbon beta oriented
side chain attached to 17th carbon.

43. Question 18
• Name any four biologically important compounds derived from
cholesterol
• Bile acids
• Steroid hormones
• Vitamin D FROM 7-dehydrocholesterol

44. Question 19
• Biologically important derivatives of cholesterol
• Glucocorticoids ,mineralocorticoids, testosterone, estrogen and bile
acids

45. Question 20
• Role of HDL as scavenger of cholesterol
High density lipoproteins are synthesized in the liver as discoidal
particles– nascent HDL. They contain free cholesterol and phospholipids
(mostly lecithin) and apoproteins (A, CII, E etc.).
Role of LCAT in HDL metabolism : The plasma enzyme lecithin-cholesterol
acyl transferase (LCAT) catalyses the esterification of free cholesterol (by
fatty acid of lecithin) present in the extrahepatic tissues and transfers to
the HDL.

46. • Apoprotein A promotes the activity of LCAT.
• HDL also accepts free cholesterol from other lipoproteins in
circulation and cell membrane of peripheral tissues
• Any free cholesterol taken up by HDL undergoes LCAT-catalysed
esterification.
• Due to the addition of cholesterol, HDL particles become spherical.
The HDL particles, with cholesteryl ester trapped inside, enter the
hepatocytes by areceptor-mediated endocytosis.
• In the liver, the cholesteryl esters are degraded to cholesterol. The
latter is utilized for the synthesis of bile acids and lipoproteins or
excreted into bile (as cholesterol

48. Question 21
• Name the ketone bodies
Acetoacetate, betahydroxybutyric acid and acetone