11 biosynthesis of other lipids 20141115
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Biosynthesis of Membrane Lipids
Glycerolipids and Sphingolipids Synthesis of new membrane requires production of phospholipids On smooth ER surfaces
CTP
PPi Phosphatic acid phosphatase
Pi
CMP
Glycerophospholipids
Head group HO
CTP
PPi
CMP
Biosynthesis of Glycerolipids (glycerol backbone)
Glycerophospholipids
Phosphodiester linkage
Examples of head groups: - inositol in phosphatidylinositol - glycerol in phosphatidylglycerol
Non-polar (hydrophobic)
Polar (hydrophilic)
Amide linkage
N-acylation
(C-18)
Biosynthesis of sphingolipids (backbone: C-18 amino alcohol)
(C-16)
C
O
R
C
O
R
(N-acyl-sphingosine)
choline
Head-group attachment
(Sphingophospholipid)
(Glycosphinolipid)
Desaturation
(ARA)
ARA is a precursor for Eicosanoids
Eicosanoids - Potent signaling molecules - e.g. Prostaglandins and thromboxanes
Arachidonic acid (ARA)
Prostaglandins - Trigger pain and inflammation - Regulate the release of mucins for stomach protection
Thromboxanes - Induces constriction of blood vessels, platelet aggregation,
blood clotting
Biosynthesis of Eicosanoids
Prostaglandin H2 synthase (COX) - 2 enzyme activities (1 and 2) - 2 isozymes: COX-1 and COX-2, very similar in structure (both with
activities 1 and 2) - COX-1: making prostaglandins for regulation of gastric mucin secretion - COX-2: making prostaglandins for induction of inflammation, pain, fever
Thromboxanes
Prostagladin H2 Other prostaglandins
Different pain killers/anti-inflammatory drugs targeting COX
- Inhibition of cycloxygenase of COX-1 and COX-2 - Side effects: stomach ulcers - Low dosage of aspirin: reduces risks of heart attack and stroke due to
lowered thromboxane production - Vioxx: COX-2 specific; no side effects on stomach but increased risks
of cardiovascular disease; taken off the market - Structural analysis of COX-1 and COX-2 for design of COX-2 specific
pain killers.
Salicylic acid - Natural pain-killer found in bark of willow trees used by ancient Greek - Structure similar to aspirin - Bitter tasting and unpleasant side effects including severe stomach irritation - Plant hormone to suppress diseases and wilting
Salicylic acid
Cholesterol Biosynthesis
Condensation of 3 acetate units
Conversion to a C-5 unit
(C-6 intermediate)
condensation of 6 isoprene units
3 acetyl-CoAs to 1 isoprene 6 isoprenes to 1 cholesterol 18 acetyl CoAs
Ring closure
4 fused rings: steroid nucleus
OVERVIEW OF BIOSYNTHESIS (acetyl-CoA)
(C-30)
(C-27)
Formation of mevalonate and activated isoprene units
3 acetyl-CoA 1 activated isoprene unit
Target for cholesterol-
lowering drug
CO2
Same as the first 2
steps in ketone body
formation
Cholesterol-lowering drugs - Statins - Competitive inhibitor of HMG-CoA reductase - HMG-CoA reductase converts HMG-CoA to mevalonate
5 3
Isomerization
Formation of Squalene
(C-10)
(C-15)
Tail Head Tail Head
Head
Head
Tail Tail
(C-15)
(C-15)
(C-30 unit, first discovered in sharks, Squalus spp.)
HO
Ring closure converts squalene to steroids
3 3 3
~20 rxns
Removal of methyl groups (CH3)
Reduction of double bonds
Cholesterol
3
3
Fatty acyl-CoA
CoA-SH
Acyl-CoA-cholesterol
acyl transferase
Lipoprotein
particles
(chylomicrons,
VLDL, LDL, HDL)
(C-30)
(C-27)
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