LIPIDS:
STRUCTURE, CLASSIFICATION AND
FUNCTIONS
LECTURE OBJECTIVES:
 At the end of lecture the student should be able to;
1. Define lipids
2. Classify lipids
3. Describe the functions of various classes of lipids.
4. Justify that cell membrane is made up of phospholipids
5. Justify that milk is needed for post natal development of brain
(phospholipids, glycolipids, sphingolipids).
6. Discuss the clinical significance of lipids (obesity, diabetes mellitus,
cardiovascular diseases, vitamin D deficiency, hypertension, storage
diseases)
LIPIDS:
 Heterogeneous compounds
 Insoluble in water
 Soluble in organic solvents like ether
 Esters of Fatty acids with alcohol.
CLASSIFICATION
CLASSIFICATION OF LIPIDS:
EXAMPLES OF LIPIDS:
Simple
Compound or
Derived
Conjugated or Complex
Triacylglycerol Lipoproteins
Cholesterol
Ceramide
Retinol
Waxes
-
Glycolipids (Cerebroside,
Ganglioside)
Phospholipids
Sphingolipids (Glyco and
Phospho)
Sulpholipids
-
Cholcalciferol
Ketone bodies
Fatty acids
Steroid
hormones
Prostaglandins
Ecosanoids
FUNCTIONS OF LIPIDS:
FUNCTIONS OF SIMPLE LIPIDS
–
–
–
–
–
Neutral lipids
Stored in adipose tissue
Give body contours
Insulators
Store energy
COMPOUND LIPIDS: FUNCTIONS
Lipid with some other non-lipid group
•
•
•
•
•
Phosphatidyl Inositol Triphosphate
Phosphatidyl Ethanolamine
Phosphatidyl Serine
Phosphatidyl Choline
Phosphatidyl glycerol
CLASSIFICATION OF GLYCOLIPIDS
NEUTRAL GLYCOSHPINGOLIPIDS
•
Cerebroside (ceramide monosaccharide)
– Most common glycolipid of membranes
Post natal developmnent of brain, peripheral nerves, myelin sheath
• Globoside (ceramide oligosaccharide)
– Lactosylceramide
– Forssman Antigen (Blood Groups)
ACIDIC GLYCOSPHINGOLIPIDS
•
•
•
Negatively charged
Acidic sugars (Sialic Sugar or NANA)
Classified as
– Ganglioside
• Ganglion cells, nerve endings
• One or more molecules of NANA
• Nomenclature
– G-ganglioside
– M,D,T or Q- number of NANA
– Integer numbers for addition
saccharide units
• Lipid Storage diseases
– Sulfatide (Sulfoglycosphingolipdis)
• Sulfated galactosyl residues
• Nerve tissue and kidney.
LIPOPROTEINS
LIPOPROTEIN STRUCTURE
•
•
•
Phospholipid membrane
Membrane proteins called Apolipoproteins
Core
– Triacylglycerol (TAG)
– Cholesterol
– Cholesteryl Esters.
CLASSIFICATION OF LIPOPROTEIN
Lipoproteins Site of
Synthesis
Apo-lipoprotein
Function
Chylomicron Intestine
B48
C-II, E, D
B100
C-II, E, D
Transport of dietary
lipids around the body
Transport of endogenous
lipids (TAG) around the
body
Transport of endogenous
lipids (TAG) around the
body
Transport of Cholesterol
around body
VLDL
Liver
IDL
Plasma
B100
C-II, E
LDL
Plasma
B100
HDL
Intestine and A-I
Liver
Gives C-II, E, D
Transport Cholesterol
from peripheral tissues to
liver
Lipo-proteins Density
Triacyl- Cholesterol,
glycerol Choleteryl
%
Ester
%
Phospholipids
%
Protein
%
Chylomicron ≤ 0.95
90
5
3
2
VLDL
1.00 – 1.05 60
20
15
5
LDL
1.10 – 1.15 8
50
22
20
HDL
≥ 1.20
25
30
40
5
DERIVED LIPIDS
•
Molecules/group that are
made from a lipid.
–
–
–
–
–
–
–
Fatty acid
Glycerol
Sterol
• Cholesterol
• Sex hormones
Ketone bodies
Bile acids/salts
Fat soluble Vitamins
A,D,E and K.
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