bioc/dent/phcy 230 lecture 8
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BIOC/DENT/PHCY 230 LECTURE 8. Transport and delivery of dietary lipids. dietary triacylglycerol (TAG) and cholesterol are delivered to target tissues by lipoproteins the four main lipoproteins are: chylomicrons VLDL LDL HDL. - PowerPoint PPT PresentationTRANSCRIPT
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BIOC/DENT/PHCY 230
LECTURE 8
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Transport and delivery of dietary lipids
dietary triacylglycerol (TAG) and cholesterol are delivered to target tissues by lipoproteins
the four main lipoproteins are:
chylomicrons
VLDL
LDL
HDL
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each lipoprotein has a characteristic combination of lipids and apoproteins
chylomicrons and VLDL are the primary transporters of TAGs to target tissues
LDL and HDL are the primary transporters of cholesterol
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Structure of a general lipoprotein
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Lipoprotein lipase liberates free fatty acids from TAGs
Chylomicrons and VLDLs have apoprotein CII, which anchors the lipoprotein to lipoprotein lipase
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Fatty acid synthesis excess carbohydrate is converted to fatty acids and TAGs
fatty acid synthesis occurs in the cytoplasm of a variety of cell types
synthesis of fatty acids is based around acetyl-CoA
acetyl-CoA is a precursor for malonyl-CoA
it is in the form of malonyl-CoA that most carbons are introduced into fatty acid synthesis
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Synthesis of malonyl-CoA
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In vertebrates:
fatty acid synthesis is catalysed by a multi functional enzyme, fatty acid synthase
fatty acid synthase contains all the enzyme activities required for the remainder of fatty acid synthesis
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Synthesis of Acetyl-ACP and Malonyl-ACP
Acetyl-CoA and malonyl-CoA are attached to an acyl carrier protein (ACP)
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Initiation of fatty acid synthesis
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-oxidation
synthesis
NADPHNADP+ + H+
NADPHNADP+ + H+
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Elongation continues with the addition of malonyl-CoA
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8 acetyl-CoA + 14 NADPH + 7ATP
palmitate + 14 NADP+ + 8 CoA + 7ADP + 7 Pi + 6H2O
Overall equation for the synthesis of palmitate (16:0)
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Synthesis of TAGs
fatty acids are added onto a glycerol backbone
glycerol -3- phosphate can be derived from:
DHAP (glycolysis)
phosphorylation of glycerol
by glycerol kinase
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Regulation of fatty acid synthesis fatty acids synthesis can be regulated in a number of ways
acetyl-CoA carboxylase represents a major control point
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acetyl-CoA
citrate
insulin
+-palmitoyl-CoA
glucagon
inactive dimer
active polymer
inactive acetyl-CoA carboxylase is found as a dimer
polymerisation activates the enzyme
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Excess citrate is shuttled to the cytoplasm
glucose
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NADH NADPH
NADPH supplies the reducing power for fatty acid biosynthesis
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NADPH is generated by the Pentose Phosphate Pathway
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The take home message
dietary lipids are delivered to target tissues by lipoproteins
excess fuels can be converted fatty acids
fatty acid synthesis has many features in common with -oxidation
acetyl-CoA carboxylase represents a major control point for fatty acid synthesis
reducing power in the form of NADPH is supplied by the pentose phosphate pathway