fatty acid metabolism 1 Flashcards
lipid storage
as a triacylglycerol
cis and trans unsaturated fatty acids
- double bonds can be cis or trans
- trans fatty acids are rare in natural products
trans fatty acids
- formed by hydrogenation of vegetable oils to form margarines
- widely used in snacks, biscuits
- associated with greater risk of coronary heart disease
properties of fatty acids
- hydrophobic tail and hydrophilic head- amphipathic; act like detergents
- saturated lipids often solid at room temp
- unsaturated lipids often liquid at room temp
- animal fat 40-60% saturated, with little poly-unsaturated FAs
- plant oils 80-90% unsaturation
triacylglycerol
- fatty acids stored in adipose tissue esterified to glycerol- ester linkage between fatty acid carboxyl and glycerol hydroxyl group
- have 3 FAs esterified to glycerol- it is highly reduced [therefore high calorific value], it is virtually anhydrous, forms droplets within cells
oxidation [breakdown] of fatty acids
- major constituent of triacylglycerol
- mobilized form adipose tissue during prolonged fasting, starvation and stress
- oxidised by the liver and muscle
- broken down into 2 carbon acetate units by beta- oxidation in mitochondria
- acetate enters TCA cycle, yielding ATP
mobilization of FAs
- glucagon [fasting] or adrenaline [stress] activate hormone-sensitive lipases which hydrolyse triacylglycerol in adipose tissue to free FAs and glycerol
- free FAs are released to the circulation bound to plasma albumin
- FAs released to target tissues; cross into cytosol of cell
fate of glycerol
- transported to liver, phosphorylated to glycerol 3-phosphate and converted to DHAP
- DHAP used in glycolysis or glucogenesis
fate of fatty acids
- taken up by tissues- freely cross membrane
- convicted to acetate units by b-oxidation
beta- oxidation of fatty acids
- long chain fatty acids are first activated in the cytosol to form thiol esters with coenzyme A- requires ATP
- LC fatty acids then imported into mitochondria for beta-oxidation
- beta-oxidation generates NADH, FADH2, acetyl CoA
import of LCFAs into mitochondria
CoA esters cant cross inner mitochondrial membrane
- LC fatty-acyl group transferred to carnitine
- this is then transported into mitochondrial matrix
- LC fatty acyl group transferred to CoA
canitine
- obtained form meat in diet
- synthesised in liver and kidney, supplied to muscles by kidney via blood
- carnitine deficiency can lead up to build up of toxic LCFAs- neurological damage
regulation of beta-oxidation
regulated by the supply of substrate:
- depends on rate of lipolysis in adipocyte
- regulated by hormones e.g. glucagon, adrenaline
- malonyl CoA inhibits CPTI enzyme [uptake of LCFA into mitochondria]
ketone bodies: an alternative fuel
- synthesised from acetyl CoA in liver mitochondria
- occurs when levels of acetyl CoA are high from b-oxidation e.g. starvation, uncontrolled diabetes
ketone body synthesis
2 ketone bodied formed: acetoacetate and 3-hydroxybutyrate [acetone also formed but excreted in breath].
acetoacetate reduced to 3-hydroxybutyrate when [NADH] high, [NADH] increases in liver when b-oxidation active
