Transcript GLCOLIPIDS(GLYCOSPHONGOLIPIDS)

GLCOLIPIDS(GLYCOSPHONGOLIPIDS)
• Ceramide+carbohydrate
(glucose,galactose,oligosacchride side
chain)=GLYCOLIPID
• Cerebrosides: contain a single moiety,
principally galactose
• Sulfatides: sulfuric esters of
galactocerebrosides
• Gangliosides: contain a complex
oligosaccharide moiety
CEREBROSIDES.
• Ceramide+glucose or galactose(mostly)
• Occur in the white matter of the brain and in
the myelin sheaths of the nerve fibres.
• There are different types of cerebrosides
depending upon the differences in the type of
the fatty acid and the monosacchride moiety.
• Examples;cerebron,nervon,oxynervon and
kerasin.
• Acommon fatty acid present in these
compounds is 24 carbon containing fatty acid
known as cerebronic acid.
• A more complex glycolipid is ceramide
trihexoside,ceramide-glucose-galactosegalactose.
• GANGLIOSIDES.
• Ceramide-glucose-galactose-N
acetylgalactosamine-N acetylneuraminic
acid(sialic acid)
• Gangliosides occur in brain spleen,RBCs and
nerve cells.
• In the brain gangliosides contribute about
6%of the membrane lipids in the brain.
• One important example of gangliosides is GM₁
It occurs in the itestinal cell membranes and
acts as the site of attachment to cholera toxin.
• Its structure is ceramide-glucose-galactose-N
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N-acetylneuraminic acid
acetylgalactosamine-galactose
Globosiodes
• Closely related to glycolipids.
• Said to be mucolipids
• Ceramide-glucose-galactose-galactose-Nacetylgalactosamine
Clinical significance of sphingolipids
Blood groups determined by various glycolipids on RBCs
Type 0
R
GlcNAc
Fucose
Galactose
Type A
R
Type B
R
Sialic acid (NANA)
• SULPHOLIPID are sulfate esters of
glycolipids.The sulfate group is esterified with
the –OH group of the hexose moiety of
molecule.
• Most abundant in the white matter of brain.
STEROIDS AND STEROLS
• A large number of compounds found in nature
occuring in nonsponifiable fraction of lipids
belong to class of compounds called steroids.
• Their parent nucleus is cyclopentanoperhydrophenanthrene,which consists of four rings
fused together and have total of 17 carbon.
• Steroids with eight to ten carbon atoms in the
side chain and a hydroxyl group at carbon no 3
are classified as sterols.
• Cholesterol is the major sterol in the animal
tissues.others include ergosterol,bile
acids,male and female sex hormones and
hormones of adrenal cortex.Cardiac glycosides
and some alkaloids also have steroid
components.
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CHOLESTEROL is the most abundant sterol.
Normal plasma levels are from 150-220mg/dl.
Structural component of cell membranes.
In pecialized tissues cholesterol is precursor of bile
acids, steroid hormones and vitamin D.
• The liver plays a central role in the regulation of body’s
cholesterol homeostasis.
• Cholesterol enters into the liver cholesterol pool either
through diet or by the denovo synthesis of cholesterol
by extrahepatic tissues and liver it self.
• Cholesterol is eliminated from the liver as
unmodified cholesterol in the bile or it can be
converted into bile salts that are secreted into
the intestinal lumen.
• It can also serve as a component of plasma
lipoproteins sent to the peripheral tissues.
• Imbalance between cholesterol eflux and
influx leads to atherosclerosis and coronary
artery diseases.
• Cholesterol occurs both in free and bound
form with fatty acids known as cholesteryl
esters.Bound form is more hydrophobic.
• Plant sterols such as sitosterol is poorly absorbed
by humans.
• Plant sterols appear to block the absorption of
dietary cholesterol.
• This has led to clinically useful dietary treatment
for hypercholesteremia.Daily ingestion of plant
steroid esters (in the form of commercially
available trans fatty acid free margarine)is one of
the dietary strategies leading to the reduction of
plasma cholesterol levels.
• 7-DEHYDROCHOLESTEROL occurs mainly in
skin.it is converted to vitamin D₃ when
exposed to sunlight.
• ERGOSTEROL is a main sterol of fungi and
yeast.when irradiated by ultraviolet rays,it is
converted to vitamin D₂.
Lipoproteins
Lipids must be transported to the various tissues to
accomplish their metabolic functions. Because of
their insolubility, they are transported in plasma in
macromolecular complexes called Lipoproteins.
Chemistry:
Lipoproteins are spherical particles with non polar
lipids (triglycerides and cholesterol esters) in their
core and more polar lipids (phospholipids and free
cholesterol) oriented near the surface.
They also contain one or more specific proteins called
apolipoproteins, that are located on their surface.
functions of the lipoproteins
Function
Lipoprotein
Chylomicro Transport of exogenous triglyceride
ns
VLDL
Transport of endogenous triglyceride
LDL
Transport of cholesterol from liver to other
tissues
HDL
Transport of cholesterol from peripheral
tissues and other lipoproteins to liver