Fatty acids

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Prostaglandins and leukotrienes
-Eicosanoids.
-Potent paracrine effects
-Cannot travel long distances
FATTY ACIDS
-Long hydrocarbon chains with a terminal carboxylate (COO-) group.
-Highly reduced – energy dense.
-MUFA: mono-unsaturated fatty acids
-PUFA: poly-unsaturated fatty acids
-Naturally occurring Fatty Acids are cis not trans
-Industrial production of MUFA + PUFA fats/oils – yield trans isomer fats.
omega (last) = w
The position of the C=C double bond can be denoted:
-In relation to the C number (1st C is the C atom of the COO-)
-In relation to the omega C atom e.g. w3 would be 3 carbons back from the omega carbon.
Saturated fat – no C=C double bonds
Palmitic Acid = C16
Stearic Acid = C18
-solid at room temperature.
Unsaturated fat – contains C=C double bonds
Oleic acid = monounsaturated fatty acid ---> trans isomer = Elaidic acid
Linoleic acid = polyunsaturated fatty acid (more than 1 C=C double bond – 2 double bonds)
-Unsaturated fats allow membrane to be more fluid.
-They bend and pack in a less ordered way.
-liquid at room temperature.
EPA: Eicosapentaenoic acid – 5 double bonds
DHA: Docosahexenoic acid – 6 double bonds
Essential fatty acids
PU fatty acids that have more than 2 C=C bonds at least 1 of which is beyond C9.
-Linolenic acid (C18:3) – omega 3 fatty acid
-Converted to arachidonic acid – ARA (C20:4)
-Linoleic acid (C18:2) – omega 6 fatty acid
-Converted to eicosapentaenoic acid (C20:5) – EPA
-ARA and EPA are used to synthesise eicosanoids.
Eicosanoids (prostaglandins and leukotrienes)
-Derived from C20 PUFAs – ARA, ESA and EPA.
-Synthesis pathways
-cyclooxygenase (COX) pathway – prostaglandins and thromboxane.
-lipoxygenase (LOX) pathway – leukotriene.
-Bind specific plasma membrane receptors.
-Functions as local signalling molecules.
-Play important roles in:
*Inflammation – COX2 inhibtors are widely prescribed NSAIDs e.g. aspirin
*Regulation of vascular tone,
Triacylglycerides
-3C alcohol = Glycerol.
-Stored in adipose tissue
-1g of triglycerides yields 38kJ of energy.
-No solvation – takes up less space than CHO.
Lipases: cleave ester bonds of triglycerides to release fatty acids.
GlyceroPhospholipids (GPLs)
-Simplest GPL is phosphatidate.
-It is glycerol 3 phosphate esterified with 2 FA (diacylglycerol) with phosphate group
attached to the 3rd OH group.
Polar alcohol compounds can be esterified to the PO4 group
-Choline – Phosphatidylcholine – major component of biological membranes.
-Serine
-Ethanolamine
-Inositol ---> sugar alcohol – makes neurotransmitters and steroid hormones bind to their
receptors in the brain, important in cell signal transduction.
-Glycerol: C3 alcohol.
GPLs are composed of fatty acid, glycerol, phosphate and alcohol.
-Phospholipases breakdown GPLs.
Phospholipase A2 (snake venom) - cleaves the SN-2 acyl chain, releasing arachidonic acid.
-Lysolecithin:- breakdown product of this reaction, biological detergent, dissolves the
membranes of red blood cells causing them of rupture.
GPL Properties
-Amphipathic molecules.
-Polar PO4 and alcohol groups: polar head
-Non-polar hydrophobic FA chains: non-polar tail
-Integral to the role of GPL in biological membranes.
Cholesterol increases membrane fluidity deep in membrane.
Cholesterol decreases membrane fluidity near surface.
Glycolipids
-Main class is Glycosphingolipids – simplest glycosphingolipid is a ceramide.
-They’re abundant in nerve cell membranes.
-Nerve impulse transmission.
-Cell-cell recognition.
-Molecular recognition – binds glycoprotein hormones & bacterial toxins.
-Sphingolipidoses: defects glycosphingolipid metabolism – fatal neurological disorders.
-Membrane lipids based on an 18C amino alcohol rather than glycerol.
-Parent compound is ceramide.
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