2. *
*Greek word – chole = bile
Steros = solid
Ol = alcohol
*All cells can synthesize cholesterol .
*In a 70 kg man , 140 g cholesterol is present
*It is a light yellow crystalline solid .
*It is soluble in chloroform & other fat solvents .
3. *
*More important animal steroid which form other
steroid compounds form .
*Widely distributed in animal tissues .
*Absent in prokaryotes .
*In plants , cholesterol is absent , but other
steroids are present .
*In bacteria & plants compounds have similar to
steroids , known as hopanoids.
4. *
*Level of cholesterol in blood is related to
atherosclerosis and myocardial infarction .
*Abnormally cholesterol metabolism lead to
cardiovascular accidents and heart attacks .
5. *
1) CELL MEMBRANE
2) NERVE CONDUCTION
3) BILE ACIDS AND BILE SALTS
4) VITAMIN D3
5) ESTERIFICATION
6) STEROID HORMONES
7. *
*Cholesterol is first hydrolyzed by cholesterol
esterase .
*Free cholesterol is incorporated to bile salts
micelle & absorbed into mucosal cell .
*Absorption needs micelle formation .
*There is specific protein in mucosal cell
which facilitates transport of cholesterol .
8. *
*Inside mucosal cell cholesterol is re-esterified and form
chylomicrons .
*Chylomicrons reach blood stream through lymphatics ( lacteals ) .
*This dietary cholesterol reaches liver through chylomicrons
remnants .
*Plant sterols decrease absorption of cholesterol .
*NPCH-1 protein is involved in absorption of cholesterol .
*Therapeutic effect of esetimibe drug is by interfering with function of
protein .
9. *
*Major sites of cholesterol synthesis are liver
, adrenal cortex , testis , ovaries , intestine
.
*All nucleated cells can synthesize cholesterol
including arterial wall .
*Enzymes are partly located in endoplasmic
reticulum and partly in cytoplasm .
10. 2 * acetyl-CoA
Acetyl-CoA is provided by ATP-citrate lyase
reaction as in case of FA synthesis .
1)
condensation
CoA
Acetoacetyl-CoA
synthase
Acetoacetyl-CoA
13. Production of 5
carbon unit
mevalonate
5-phosphomevalonate
Isopentenyl
pyrophosphate
3-phospho 5-
pyrophosphomevalonate
5-pyrophosphomevalonate
kinase
decarboxylase
kinase
kinase
ATP
ATP
ATP
ATPCO2
17. *
1)Regulation of transcription :-
Regulatory enzyme is HMG-CoA .
Long term regulation involves regulation
of transcription of enzyme .
When sufficient cholesterol is present in
cell , transcription of gene for enzyme is
suppressed & cellular synthesis of
cholesterol is decreased .
18. *When cholesterol is low in diet ,
transcription is increased .
*A specific recognition sequence known as
STEROL REGULATORY ELEMENT (
SRE ) .
*SRE binding by STEROL
REGULATORY ELEMENT BONDING
PROTEIN ( SREBP ) is essential for
transcription of these genes .
*When cholesterol levels are sufficiently
high , SREBP remains as an inactive
precursors .
19. *
*Short term regulation is by covalent
modification of HMG-CoA .
*Cyclic-AMP mediated cascade
phosphorylation of enzyme which is
inactive .
*Dephosphorylation form is active .
*Activity of HMG-CoA reductase is also
regulated by rate of degradation of
enzyme protein .
20. *
*Insulin & thyroxine = increase activity
*Cortisol & glucagon = decrease activity
DRUGS
*Lovastatin and statin group of drugs
are competitive inhibitors of enzyme.
*So , they are used in clinical practice to
reduce cholesterol level in body .
21. *
*Total body cholesterol = 130-150g
*Transport of cholesterol
*LDL = liver-peripheral tissue
*HDL = peripheral tissue-liver
1) Incorporated in cell membrane
2) Metabolized to steroid hormones , especially in adrenal
cortex & gonads .
3) Esterified with saturated FA &stored in cell. ACAT (acyl
cholesterol acyl transferase) helps in reaction .
4) Esterified with PUFA by action of LCAT ( lecithin
cholesterol acyl transferase ) and finally excreted through
liver .
22. *
*Average diet = 300 mg/day
*Cholesterol synthesis = 700 mg/day
*Out of this 1000 mg/day , 500 mg/day
of cholesterol is excreted through bile .
*Partly re-absorbed from intestine .
*Vegetables contain plant sterols which
inhibit reabsorption of cholesterol .
23. *
*Unabsorbed cholesterol is acted upon
by intestinal bacteria to form
cholestanol and coprostanol .
*These are excreted . ( fecal sterols )
*About 500 mg of cholesterol is
converted to bile acids which are
excreted in bile as bile salts .
25. *
*A major role in controlling of plasma levels of
LDL cholesterol .
a) Liver synthesizes cholesterol .
b) Liver removes cholesterol from lipoprotein
remnants and HDL .
c) Liver is only organ that can excrete
cholesterol through bile .
d) Liver converts cholesterol to bile acids.