Lipids are organic compounds that contain fatty acids and glycerol. They are synthesized in the liver and adipose tissue from acetyl-CoA and malonyl-CoA through a repeated cycle of reactions catalyzed by the fatty acid synthase complex. Lipids are insoluble in water and must be transported through the body within lipoproteins such as chylomicrons, VLDL, LDL, and HDL. Chylomicrons transport dietary lipids from the intestine to tissues, while VLDL transports lipids from the liver to tissues and LDL transports cholesterol to tissues. HDL is responsible for reverse cholesterol transport from tissues back to the liver.

1. SUBMITTED TO- DR. DEEP PRAKASH SAIKIA
ASST. PROFESSOR, CVSC, KHANAPARA
SUBMITTED BY- DR. ANAMIKA MAZUMDAR
2020-VMK-04
LIPID SYNTHESIS AND
TRANSPORT

2. LIPIDS
 Lipids are organic compounds that contain hydrogen,
carbon and oxygen atoms, which forms the framework
for the structure and function of living cells.
 These organic compounds are non polar molecules
which are soluble only in non polar solvents and
insoluble in water.
 Lipids are polymers of fatty acids that contain a long,
nonpolar hydrocarbon chain with a small polar region
containing oxygen.
CLASSIFICATION OF LIPIDS-
1. Simple lipids Eg: fats, waxes
2. Complex lipids Eg: glycolipids, phospholipids
3. Precursor and derived lipids Eg: Fatty acids

3. WHAT IS THE NEED FOR
SYNTHESIS
 The fat/lipid that we consume in our
diet, they get digested into fatty acid
and glycerol. These two are simplest
form of fat and gets stored in the
adipose tissue as a triacylglycerols
(TAG).
 The adipose tissue is the largest fuel
reserve of the body. The excess
carbohydrate gets converted into fatty
acid and then fatty acid and glycerol
together form TAG which is stored in
adipose tissue.
 Body’s preferred energy source is
glycogen. Glycogen degrades into
glucose and glucose after entering
glycolysis pathway generates ATP.
 When glycogen starts depleting, body
shifts for fatty acid oxidation where
TAG by lipolysis convert to fatty acid
and glycerol. This fatty acid by
oxidation forms Acetyl CoA (beta

4. Fatty Acid Synthesis
 Two fatty acid (PUFA) cannot be synthesised in our
body. (linoleic acid and linolenic acid)
 Occurs mainly in liver and adipocytes (mammals)
 FA synthesis and degradation occur by two
completely separate pathways
 When glucose is plentiful, large amounts of acetyl
CoA are produced by glycolysis and can be used for
fatty acid synthesis
 Tissues involved- adipose tissue, liver, kidney,
lactating mammary gland
 Location- cell cytoplasm (synthesis of fatty acid)
 -mitochondrial matrix (beta oxidation)

5. STEP 1- PRODUCTION OF ACETYL COA &
NADPH
Acetyl CoA, the precursor of fatty acid synthesis is produced from
pyruvate, ketogenic amino acids, fatty acid oxidation and by
alcohol metabolism. It is a substrate for TCA cycle and a precursor
for fatty acids, ketone bodies and sterols.
NADPH is produced
from pentose
phosphate pathway by
malic enzyme

6. STEP 2- CONVERSION OF ACETYL COA TO
MALONYL COA
 This process regulates the whole process and this molecule inhibit
the beta oxidation of fatty acid. Malonyl CoA inhibit the carnitine
acyl transferase I enzyme. In this step CO2 fixation takes place and
is ATP dependent. It requires the enzyme acetyl CoA carboxylase.
This enzyme is biotin dependent. Biotin acts as co2 carrier.

7. STEP 3- REACTIONS OF FATTY ACID
SYNTHASE COMPLEX
 It is a multi enzyme complex which exists as a dimer. The two
monomers of the dimer exhibit seven different enzyme activities.
The –SH of 4’ phosphopantethein of one monomer is in close
proximity of the -SH of the cysteine residue of the ketoacyl
synthase of the other monomer, suggesting a ‘head to tail’
arrrangement of the two monomers. Thus two acyl chains are
produced simultaneously.Therefore the naturally available fatty acid
is even carbon fatty acid. There are 6 different reaction of fatty acid
synthesis.

8. 6 REACTIONS OF FATTY ACID SYNTHASE
COMPLEX
Each segment of the disc
represents one of the six
enzymatic activities of the
complex
Once malonyl-CoA is synthesized, long
carbon FA chains may be assembled in
a repeating four –step sequence.
With each passage through the cycle the
fatty acyl chain is extended by two
carbons.
When the chain reaches 16 carbons, the
product palmitate leaves the cycle.

9. 6 REACTIONS OF FATTY ACID SYNTHASE
COMPLEX
 Initially a priming molecule of acetyl-
CoA combines with a cysteine-SH
group catalyzed by acetyl
transacylase.
 The acetyl group from acetyl CoA is
transferred to the cys-SH group of the
beta-ketoacyl ACP synthase.
 The processes involved are-
condensation, reduction, dehydration,
reduction.
 These steps are repeated till a fatty
acid with 16 carbon atom is
synthesized.

10. TRANSPORT OF LIPIDS
 Since lipids are insoluble in water, these are
transported in the form of lipoprotein.
CLASSIFICATION OF LIPOPROTEIN-
1. Chylomicron
2. Very Low Density Lipoprotein
3. Low Density Lipoprotein
4. High Density Lipoprotein
COMPONENTS OF LIPOPROTEINS-
1. Lipids (phospholipids, cholesterol, triacylglycerol,
cholesteroylester)
2. Proteins

11. TRANSPORT
 Chylomicrons are synthesized in the small intestine
from dietary fat and VLDL, LDL and HDL are
synthesized in the liver and small intestine.
 Chylomicrons enter the liver and are packaged into
VLDL.
 VLDL is involved in the transport of triacylglycerol
(TAG) from the liver to extra hepatic tissues.
 LDL transports cholesterol ( so-called bad cholesterol)
to tissues and HDL is responsible for ‘reverse
transport’ or removal of cholesterol (so-called good
cholesterol) from tissues.
 The term ‘bad’ and ‘good’ refer to the nature of
transport. For eg, the ‘good’ cholesterol refers to
cholesterol being carried by HDL, which is meant to
be routed to the liver for bile formation, or excretion,
thus leaving the body and not deposited, like LDL,
into blood vessels.