2. Introduction
O Lipids are a heterogeneous group of
compounds…….
O They are water insoluble organic molecules
that can be extracted from tissues by non polar
solvents.
O These include fats, oils, steroids, waxes, and
related compounds.
3. Lipid Function
O Major source of energy for the body.
O Provide the hydrophobic barriers permitting
partitioning of aqueous contents of cells and
sub cellular structures.
O Give shape and contour to the body and
protect internal organs by providing a
cushioning effect.
4. Lipid Function
O Also serves as a thermal insulator in the
subcutaneous tissues and around certain
organs.
O Act as electrical insulators, allowing rapid
propagation of depolarization waves along
myelinated nerves.
5. Classes Of Lipids
O SIMPLE LIPIDS: Esters of fatty acids with
various alcohols.
O Fats: Esters of fatty acids with glycerol. Oils
are fats in the liquid state.
O Waxes: Esters of fatty acids with higher
molecular weight monohydric alcohols.
6. Classes of Lipids
O COMPOUND LIPIDS: Esters of fatty acids
containing groups in addition to an alcohol
and a fatty acid.
O Phospholipids: Lipids containing, in addition
to fatty acids and an alcohol, a phosphoric acid
residue.
O Glycolipids (glycosphingolipids): Lipids
containing a fatty acid, sphingosine, and
carbohydrate.
7. Precursor and Derived Lipids
O Compounds produced when simple and
compound lipids undergo hydrolysis:
O These include fatty acids, glycerol, steroids,
other alcohols, fatty aldehydes, and ketone
bodies, hydrocarbons, lipid-soluble vitamins,
and hormones.
O Because they are uncharged, acyl-glycerols
(glycerides), cholesterol, and cholesteryl esters
are termed neutral lipids.
8. Fatty acids
O Chains of carbon atoms with a carboxyl group
at one end, and a methyl group at the other.
O Carbon atoms are numbered from the carboxyl
carbon (carbon No. 1).
O May be “free” or esterified form.
9. Fatty acids
O Natural fats – usually straight chain derivatives
containing an even number of carbon atoms.
O The chain may be saturated (containing no double
bonds) or unsaturated (containing one or more
double bonds).
O The cellular oxidation of fatty acids is highly
exergonic
12. Double Bond Positions
O Various conventions use Δ for indicating the
number and position of the double bonds; e.g.,
Δ9 indicates a double bond between carbons 9
and 10 of the fatty acid.
13. illustrations
O Long-chain saturated fatty acids stack tightly
and form solids at room temperature.
O Storage lipids are more saturated.
O Unsaturated fatty acids do not stack compactly
and are liquid at room temperature.
O A cis double bond forms a kink in the
hydrocarbon chain.
14. Cis and Trans Forms
O Naturally occurring unsaturated long-chain
fatty acids are nearly all of the cis
configuration.
O Trans-fatty acids are produced by fermentation
in the rumen of dairy animals and are obtained
from dairy products and meat.
15. Implications
O They are also produced during hydrogenation
of fish or vegetable oils (to produce
margarine).
O Diets high in trans fatty acids correlate with
increased blood levels of LDL (bad
cholesterol) and decreased HDL (good
cholesterol).
16. Triacylglycerols
O In vertebrates, adipocytes store large amounts
of triacylglycerols as fat droplets; they form a
large globule which may occupy most of the
cell volume.
O Adipocytes contain lipases which catalyze the
hydrolysis of stored triacylglycerols, releasing
fatty acids for export to sites where they are
required as fuel.
18. Triacylglycerols for Energy??
Carbon atoms of fatty acids are more
reduced than those of sugars – oxidation of
triacylglycerols yields much more energy
per gram, compared to oxidation of
carbohydrates.
Triacylglycerols are hydrophobic and
therefore unhydrated – no extra weight of
water that as associated with stored
polysaccharides.
19. Energy Needs
Energy needs can be met for months by
drawing on fat stores.
Human body can store less than a day’s
energy supply in the form of glycogen.
20. waxes
Waxes serve as energy stores and water
repellents:
O Biological waxes are esters of long-chain (C14
to C36) saturated and unsaturated fatty acids
with long-chain (C16 to C30) alcohols.
21. waxes
O Their melting points are generally higher than
those of triacylglycerols.
O Certain skin glands of vertebrates secrete
waxes to protect hair and skin and to keep it
pliable, lubricated and water proof.
O In waterfowls feathers are coated in waxes.
22. Phospholipids
O Contains a glycerol backbone with two fatty
acids and a phosphate group (phosphatidic
acid).
• The phosphate group is hydrophilic while the
fatty acids groups are hydrophobic.
• Because of this structure, phospholipids are
ideal emulsifiers, and the perfect structure for
cell membranes
23. Sphingosine
O Sphingolipids are derivatives of the
alcohol sphingosine.
O Present in large quantities in the brain
and nervous tissues
24. Composition
One molecule of the long-chain amino
alcohol sphingosine or one of its
derivatives.
One molecule of long-chain fatty acid.
Polar head group that is joined by either a
O-glycosidic bond or a phosphodiester
bond
27. Task Two
O What are sterols?
O Name any steroid hormone you know.
O What are the functions of sterols?
28. Concept
O Eicosanoids are paracrine hormones – act on
cells near the point of synthesis.
O Derived from the 20-carbon unsaturated fatty
acid arachidonic acid, 20:4 (Δ 5, 8, 11, 14).
O There are three classes: Prostaglandins,
thromboxanes, and leukotrienes
29. Physiological Importance Of
Lipids
O Prostaglandins stimulate contractions of the uterine
smooth muscles during menstruation and labour. Also
elevate temperature and cause inflammation and pain
O Thromboxane is a vasoconstrictor and a potent
hypertensive agent, and it facilitates platelet
aggregation.
O Leukotrienes cause bronchoconstriction as well as
being potent proinflammatory agents and play a part in
asthma.
30. Further Insights
O Phosphoacylglycerols:
O Major constituents of membranes and the
outer layer of lipoproteins, as surfactant in the
lung, as precursors of second messengers, and
as constituents of nervous tissue.
31. More Insights
O Glycolipids are also important constituents of
nervous tissue such as brain and the outer
leaflet of the cell membrane.
O Cholesterol is an important component of
membranes. It is the parent molecule from
which all other steroids in the body, including
major hormones such as the adrenocortical and
sex hormones, vitamin D, and bile acids, are
synthesized.
32. Lipoproteins
Chylomicrons :
O Vast amount of lipid in the chylomicron is
triacylglycerol.
O Only lipoprotein derived exclusively from
dietary lipids and are therefore considered
exogenous system.
O Are the largest lipoproteins.
33. Lipoproteins
VLDL
O Made in the liver from triacylglycerol and
from cholesterol that is mostly made in the
body (90%) with a small portion (10%)
derived from the diet.
O Because these lipids are made in the body,
constitutes part of the endogenous system.
O Delivers TGs from liver to peripheral tissue
(muscle for energy, adipose for storage).
34. Lipoproteins
IDL
O Contain primarily a range
of triacylglycerols and cholesterol esters.
O They are cleared from the plasma into
the liver, or further degraded to
form LDL particles.
O Transports a variety of triglyceride fats and
cholesterol.
35. Lipoproteins
LDL
O Derived from VLDL after the latter has
dumped most of its triacylglycerols in tissues
such as adipose and muscle.
O Cholesterol is the predominant lipid.
O Known as “bad cholesterol” because they can
transport their content of fat molecules into
artery walls, attract macrophages, and thus
cause atherosclerosis.
36. Lipoproteins
HDL
O Carry the most protein content.
O Cholesterol predominates over triacylglycerol
O Known as “good cholesterol” because it
removes fat and cholesterol from cells,
including within artery wall, and transport it
back to the liver for excretion or re-utilization.
37. Cholesterol
O The ratio of total cholesterol to that of HDL
can be used to evaluate susceptibility to the
development of atherosclerosis.
O The ratio should be kept under 5, ideal
cholesterol ratio is 3.5.
