Biosynthesis & metabolism of triacylglycerol & ketone bodies

1. BIOSYNTHESIS & METABOLISM
OF TRIACYLGLYCEROLS &
KETONE BODIES
BY
D.SHEEBA
1ST M.SC
BIOCHEMISTRY

2.  The requirement of organisms ,most of the fatty
acids synthesized or ingested by an organism either
incorporated into triacylglycerols for storage of
metabolic energy or incorporated into the
phospholipid membrane.
 The organisms that are not actively growing but have
abundant food supply , donot convert most of their
fatty acids in to storage fats; but during rapid growth
the synthesis of new cell membranes require
membrane phospholipids synthesis.

3.  Both triacylglycerols and phospholipid syntheses
begin at the same point – The formation of fatty acyl
esters of glycerols.
STORAGE
 Human store only about ½ kilo of
glycogen in the liver, muscle, which is
hardly enough to supply the body’s energy
needs for 12 hours.
 The total amount of stored triacylglycerols in
a 70kg man is about 15 kg,which is enough
to supply basic energy needs for 12 weeks
 When CHO is ingested in excess of capacity
to store glycogen ,it is converted into
triacylglycerols and stored in adipose tissue.

5.  Manufacture triacylglycerols as an energy-rich fuel and store
them in fruits and seeds.
 Triacylglycerol and phospholipids share 2 precursors and
many enzymatic steps in the biosynthesis in animal
tissue.
 Glycerol-3-phosphate formed in 2 ways;
I. Either from dihydroxyacetone phosphate
generated during glycolysis by the action
of cytosolic NAD-linked glycerol-3-
phosphate dehydrogenase.
II. Or from glycerol by the action of glycerol
kinase in liver and kidney.

6.  Phosphatidate –occurs in traces cell , is a key
intermediate in lipid biosynthesis.
 It can be converted either to a triacylglycerol or to a
glycerophospholipid..
 Phosphatidate is hydrolyzed by phosphatidate
phosphatase to form 1,2-diacylglycerol .
 Diacylglycerol are then converted to triacylglycerols
by transesterification with a third fatty acyl-CoA.
 In men amount of body fat remain constant for long
period.
 If CHO, protein, fats is consumed in excess of their
energy needs, the surplus is stored in the form of
triacylglycerols.

7.  This stored fat is utilized for energy during normal
body activity or during fasting.
 Triacylglycerol metabolism is influenced by
hormones such as insulin and glucagon and also by
the growth hormone and adrenalocorticoids.

8. Triacylglycerol

9.  The term ketogenesis means formation of ketone
bodies.
 The acetyl-CoA formed in fatty acid oxidation enter
the citric acid cycle if fat and CHO degradation are
approximately balanced- ketogenesis
 Acetyl-CoA is converted to acetoacetate or D-beta-
hydroxybutyrate. These compounds which together
with acetone referred as ketone bodies.
 The molecular basis that fats burn in the flame of
CHO is now evident.

12. Fundamentals of biochemistry
-S.chand (2005)
 Biochemistry – Donald Voet
& Judith Voet (2nd edition)
 Principles of biochemistry -
Lehninger