Lipids consist of glycerol and fatty acids, including saturated and unsaturated varieties. They are classified as simple or complex lipids. Lipids are absorbed in the small intestine and transported to tissues via lipoproteins such as chylomicrons, VLDL, LDL, and HDL. Lipids are stored as triglycerides in adipose tissue and liver. They provide energy through beta-oxidation in the mitochondria, producing ketone bodies when broken down, or are synthesized into fatty acids and other lipids through lipogenesis. Cholesterol is also synthesized and transported similarly.

2. Lipids consist of two parts
1. Glycerol
2. Fatty Acids
a. Saturated fatty acids
b. Unsaturated fatty acids
.Monounsaturated . Polyunsaturated
Figure 3 : Formation
of TG

3. Table 1 : Saturated fatty acids

4. Table 2 : Unsaturated fatty acids

5. Lipid metabolism
• Almost all the fats of the diet except short
chain fatty acids are absorbed from the
intestine in to the lymph.
• During digestion most triglycerides are split in
to monoglycerides & fatty acids.
• Once they reached the intestinal tract they are
re synthesized as triglycicleserides.
• From the intestinal tract they are transported in
to the blood in the form of chylomicrons.

6. • Lipo protein lipase is enzyme present in the
blood which hydrolysis triglycerides &
phospholipids in to fatty acid & Glycerol for its
storage in adipose & liver cells.
• Lipo proteins
• They are small particles much smaller than
chylomicrons but similar in composition
(TAG,cholesterol,phospholipids,&prtn)
• 1/3rd
or 1/4th
protein & remaining lipids

7. Major classes of Lipo Protein
• Very low density lipo protein
• Contains high conc of triglycerides & moderate
conc of cholesterol & TAG.
• Intermediate density lipoprotein
• Large share of TAG removed so Conc of
cholesterol & phospholipids ↑ses.
• Low density lipoprtn
• All the triglycerides are removed so high conc
of cholesterol & moderate amount of
phopholipids are seen.

8. • High density lipoprtn
• Which contain a high concentration of
protein but smaller conc of cholesterol &
Phospo lipids seen.

9. Phospholipids
• Phospholipids – contains one or more fatty
acid molecules & one phosphoric acid
radical they usually they contain a
nitrogenous base.
• The major types of phospholipids are
lecithin, cephalins & sphingo myelins.

10. Lipids are classified as simple or
complex
1. Simple lipid
a. Fatty acids
b. neutral fats (monoglyceride,
diglycerde, and triglyceride)
c. waxes
2. Complex lipids
a. Phospholipids
b. Glycolipids
c. Lipoproteins
Figure 1 :
Triglyceride
Figure 2 :
Phosphatidic acid

11. Omega Fatty acid

12. Cis- Trans Fatty
acid

13. Function of
Fat
. Energy
. Essential nutrient
. Flavor and Satisfaction
. Adipose Tissue
. Cell membrane Structure
Fat in Food
Fat in Body

14. Food Sources of
Fat
. Meat Fat (bacon, sausage….)
. Dairy Fats and products (cream, butter,
cheese..)
. Egg yolk
. Monounsaturated , polyunsaturated Fatty acid
. Vegetable oil (safflower, corn, soybean,
cottonseed, olive oil)
Animal Fats
Plant Fat

15. Characteristics Of Food Fat
Sources
. Butter, margarin, salad oils and
dressing,shirteninig fat meat
. Chees, cream portion of homogenised milk, egg
yolk, nuts, seeds, olives…..
Visible Fat
Invisible Fat

16. Digestion of
lipids
1. In mouth
mechanical digestion
Lingual Lipase
2. In stomach
mechanical digestion
Gastric lipase

17. 3. In small intestine
Bile acid, Pancreatic Lipase,
Cholesterol esterase,
Phospholipase
Triglycerid
es
2 fatty acids + Mono
glycerides
3 fatty acids + glycerolTriglycerid
es
Triglycerid
es
1 fatty acids +
Diglycerides

18. Absorption of
lipids
Figure 4 : Absorption of fat.

19. Transportation of
lipids
Source Destination Major lipids Functions
Chylomicron
s
Intestine Many organs Triglycerides,
other lipids
Deliver lipids
of dietary
origin to
body cell.
VLDLs Liver Many organs Triglycerides,
Cholesterol
Deliver
endogenously
produced
triglycerides
to body cells.
LDLs Intraviscular
removal of
triglycerides
from VLDL
Blood vessels,
Liver
Cholesterol Deliver
endogenously
produced
cholesterol
to various
organs.
HDLs Liver and
intestine
Liver and
steroid-
hormone-
Cholesterol Remove and
degrade
Cholesterol.
Table 3 Lipids are transported in the plasma as
lipoproteins.

20. Lipids
Metabolism
. Liver and Adipose tissue play a central role in
lipid metabolism.
. Adipose tissue is the main store of
triglyceride in the body.
. Lipid metabolism either lipolysis or
lipogenesis.
. Fatty acids are both oxidized to acetyl CoA
and synthesized from acetyl CoA.

21. Lipolys
is
. Complete hydorlysis of triglyceride yeild
gelycerol and 3 fatty acids.
. Fatty acids oxidiation take place in the
mitochonderia.
. Fatty acids are activated before being
catabolized (oxidized).
Fatty acid + ATP + CoA Acyl CoA + AMP
+ PPi

22. Long chain fatty acids penetrate the inner
-Mitochinderial membrane as carnitine derivatives.
Figure 5 : Role of carnitine in the transport
of long chain fatty acids.

23. - oxidation pathway of fattyβ
acids
. Many tissues are capable of oxidizing fatty
acids in the mitochondria by - oxidationβ
pathway.
. The chain is broken between the (2) and (3)α β
carbon atoms.
Figure 6 : Overview of - oxidation pathway of fattyβ
acids

24. - oxidation of fatty acids (β Figure 7)

25. The products of oxidation of fatty
acidsOxidation of fatty acids produces a large quantity of
ATP,
.example : Palmitic acid (C:16 )
7 cycles from 7 NADH + 7 FADH2
(7 x5 = 35 ATP)
7 cycles from 8 Acetyl CoA
(8 x 12 = 96 ATP)
2 ATP for the initial activation
of fatty acid
( 35 +96 – 2 = 129 molecule of ATP)
Figure 8 : acetyl
CoA product

26. Oxidation of unsaturated fatty acids occurs by
amodified - oxidation pathway (figure9)β

27. Ketonebodie
sKetogenesis occurs when there is a high rate of
fatty acid oxidation in the Liver (figure 10).
Aceto acetyl CoA
Acetyl CoA
Acetoacetate
Acetone-β hydroxy butyrate
Acetyl CoA
CoA
CoA

28. Lipogenesi
s
. The body is capable of synthesizing fatty acids in
the cytoplast of the cell from starter ( acetyl CoA +
malonyl CoA).
. Malonyl CoA is formed from Acetyl CoA
Figure 11 : Biosynthesis of Malonyl
CoA

29. . Acetyl CoA transfer to the cytoplast across the
mitochondrial membrane in the form of citrate
Figure 12 : Conversion the citrate to
Oxaloacetate and Acetyl CoA.
. The enzymes involved in fatty acid synthesis are
arranged in a complex called the fatty acid synthase
system.

31. The steps in the synthesis of fatty acid
( Figure 13)

32. Cholester
ol
Figure 14 : Cholesterol
. Cholesterol is not an energy
producing nutrient.
. It is an essential structural
component of membrane of the outer layer of plasma
lipoprotien.
• Bile acids and steriod hormones are formed from
cholesterol.
. Cholesteryl ester is a storage form of cholesterol which
is found in most tissues.

33. Acetyl CoA is the source of all carbon atoms in cholesterol
Squalene
-hydroxy- - methylglutaryl CoAβ β
Mevalonate
Farmesyl pyrophosphate
Acetyl CoA
CoA
Acetoacetyl CoA
CoA
Acetyl CoA
HMG-CoA
reductase
Cyclization

34. Reference
s
Brene, R., Levy, M., Koeppen, B., Stanton, B., (2004)
Physiology, Fifth edition. Mosby.
Fox, S., (2004) Human Physiology, Eighth edition. Mc
Graw Hill.
Hunt, S., Groff, J., (1997) Advanced Nutrition and Human
Metabolism, West Puplishing Company.
Lehninger, A., Nelson, D., Cox, M.,(1993) Principles of
Biochemistry, 2nd
edtion. Worth Puplishers.
Murray, R., Granner, D., Mayes, P., Rodwell, V., (1996)
Haper’s Biochemistry, 24th
edition, Prentic-Hall
International, Inc.
Seeley, R., Stephens, T., Tate, P., (1992) Anatomy and
Physiology,Mosby Yearbook.