This document summarizes the biosynthesis of glycerides, phospholipids, and cholesterol. It states that glycerides are the major lipids in the body and are esters of glycerol and fatty acids. Phospholipids are the main constituents of biological membranes and contain a phosphate group. Cholesterol is needed by the body but in moderation, as unhealthy levels can lead to high blood cholesterol. The document then goes on to describe the enzymatic biosynthesis processes of each compound in more detail through multiple steps.

1. Biosynthesis of
glycerides,
phospholipids and
cholesterol
-BY KRISHITA MUKHERJEE
P20CND1014
1ST M. SC., 2ND SEMESTER
PERIYAR UNIVERSITY.

2. TO BEGIN WITH THE FIRST QUESTION THAT
HOPS ONTO OUR MIND!

3. GLYCERIDES CONSTITUTE THE
MAJORITY OF LIPIDS IN THE BODY.
ALONG WITH WAXES, THEY ARE THE
LIPIDS WHICH HAVE AN ESTER AS
THE MAJOR FUNCTIONAL GROUP
AND INCLUDE: WAXES,
TRIGLYCERIDES, AND
PHOSPHOLIPIDS. IN SIMPLER
TERMS, GLYCERIDES ARE ESTERS OF
GLYCEROL AND FATTY ACIDS.
BASED ON THE NUMBER OF FATTY
ACIDS ATTACHED TO THE GLYCEROL
GROUPS, GLYCERIDES CAN BE
CLASSIFIED AS
·MONOGLYCERIDES,
·DIGLYCERIDES,
·TRIGLYCERIDES.
GLYCERIDES.

4. PHOSPHOLIPIDS ARE THE MAIN
CONSTITUENT OF BIOLOGICAL
MEMBRANES. THE SIZE, SHAPE,
CHARGE, AND CHEMICAL COMPOSITION
OF DIFFERENT PHOSPHOLIPID CLASSES
PLAY A ROLE IN THE FORMATION AND
MAINTENANCE OF THE PLASMA
MEMBRANE BILAYER OF CELLS, AS WELL
AS MEMBRANES SURROUNDING
SUBCELLULAR ORGANELLES AND
VESICLES.
THEY ARE CLASS OF LIPIDS THAT
CONSIST OF TWO FATTY ACYL
MOLECULES ESTERIFIED AT THE SN-1
AND SN-2 POSITIONS OF GLYCEROL,
AND CONTAIN A HEAD GROUP LINKED
BY A PHOSPHATE RESIDUE AT THE SN-3
POSITION.
PHOSPHOLIPIDS.

5. CHOLESTEROL IS A WAXY, FAT-LIKE
SUBSTANCE THAT YOUR BODY
NEEDS FOR GOOD HEALTH, BUT IN
THE RIGHT AMOUNTS. UNHEALTHY
LEVELS OF CHOLESTEROL CAN LEAD
TO A CONDITION CALLED HIGH
BLOOD CHOLESTEROL.
CHOLESTEROL IN YOUR BLOOD IS
CARRIED ON LIPOPROTEINS:
·LOW-DENSITY LIPOPROTEIN (LDL),
SOMETIMES CALLED “BAD”
CHOLESTEROL
·HIGH-DENSITY LIPOPROTEIN (HDL),
SOMETIMES CALLED “GOOD”
CHOLESTEROL.
CHOLESTEROL.

6. BIOSYNTHESIS
OF
GLYCERIDES!
BUT WAIT! WHAT IS BIOSYNTHESIS?

7. GLYCERIDES - ALSO KNOWN AS
ACYLGLYCEROLS - ARE MOSTLY
SYNTHESIZED BY ENZYMES OF THE
SMOOTH ENDOPLASMIC RETICULUM (ER)
OF LIVER, ADIPOSE TISSUES, LACTATING
MAMMARY GLANDS, INTESTINAL MUCOSA
AND MUSCLES. SMALLER AMOUNTS ARE
SYNTHESIZED IN THE MITOCHONDRIA.
TRIACYLGLYCEROL IS THE
MOST COMMON TYPE OF
ACYLGLYCEROL FOUND IN
THE HUMAN BODY, AND
HENCE WE WOULD
DISCUSS IT IN DETAIL!

9. AS FAR AS MONOACYLGLYCEROLS - OR
MONOGLYCERIDES - ARE CONCERNED,
THEY ARE BIOSYNTHESIZED BY THE
- ENZYMATIC HYDROLYSIS OF
TRIGLYCERIDES BY LIPOPROTEIN
LIPASE,
-ENZYMATIC HYDROLYSIS OF
DIACYLGLYCEROLS BY
DIACYLGLYCEROL LIPASE
-INTERMEDIATE IN THE
ALKANOYLATION OF GLYCEROL TO
FORM FATS.

10. BIOSYNTHESIS
OF
PHOSPHOLIPIDS!
Phospholipids are synthesized by
enzymes of smooth ER of mainly the liver,
intestinal mucosa, adipose tissue and
nerve tissue.
The commonly seen phospholipids are phosphatidic acid,
phosphatidylcholines, phosphatidylethanolamines,
phosphatidylserines, phosphatidylinositols and
phosphatidylglycerols.

12. BIOSYNTHESIS
OF
CHOLESTEROL!
In a day, around 500mg
of choloesterol is
normally synthesized by
the cytosolic and
microsomal enzymes.
Liver and intestinal
mucosa synthesize
250mg and 75mg
respectively. The rest is
largely formed in the
skin; and to some extent
in the adrenal cortex
and gonads.

13. FIRST STEP
FORMATION OF MAVALONATE

14. The malavonate formed is
phosphorylated
sequentially by ATP and
after decarboxylation, the
active isoprenoid unit -
isopentanyl diphosphate
is formed.
SECOND STEP
FORMATION OF ISOPRENOID UNITS

15. The isopentenyl diphosphate is
isomerised by the shift of a double
bond to generate dimethylallyl
diphosphate which condenses with
another molecule of isopentenyl
diphosphate forming a 10 –
carbon intermediate, geranyl
diphosphate, which further
condenses with isopentenyl
diphosphate forming farnecyl
diphosphate. 2 such molecules of
FD condense to form squalene.
THIRD STEP
FORMATION OF SQUALENE FROM 6
ISOPRENOIDS

16. Squalene can fold into a structure
which resembles the steroid
nucleus. Squalene epoxidase
catalyses the conversion of
squalene – 2.3 – epoxide. Methyl
group transfer occurs as a
cyclization takes place catalysed
by the enzyme oxido
squalene:lanosterol cyclase.
FOURTH STEP
FORMATION OF LANOSTERONE

17. In the membranes of endothelium
reticulum, the formation of
cholesterol from lanosterol takes
place, involving changes in the
steroid nucleus and side chains.
This involves a complex 19 steps
to generate cholesterol with the
intermediate formation of
desmosterol.
FIFTH STEP
FORMATION OF CHOLESTEROL

18. In the membranes of endothelium
reticulum, the formation of
cholesterol from lanosterol takes
place, involving changes in the
steroid nucleus and side chains.
This involves a complex 19 steps
to generate cholesterol with the
intermediate formation of
desmosterol.
FIFTH STEP
FORMATION OF CHOLESTEROL

19. THE PROCESS

20. REFERENCES
The references for the above produced
content have been taken from the
following sources
·HARPER’S ILLUSTRATED BIOCHEMISTRY; 28TH EDITION.
ROBERT K. MURRAY, DAVID A BENDER, KATHLEEN M. BOTHAM , PETER J. KENNELLY, VICTOR W. RODWELL, P. ANTHONY WEIL.
MCGRAWHILL PUBLICATIONS.
·WWW.LIPIDLIBRARY.AOCS.ORG
·WWW.SCIENCEDIRECT.COM