fat metabolism 1/2 WF Flashcards
fatty acids structure?
straight chain
saturated or unsaturated
carboxyl group is C1
carbon chain
double bonds can be cis (naturally occuring) or trans (synthetic)
triacylglycerol structure
fatty acids stored as esters with glycerol
triacylglycerols features?
water insoluble
liquid at body temp
digestion begins in intestine
converted mechanically into lipid droplets in the stomach
digestion of triacylglycerol in the intestine?
bile salts (natural detergents) break down triacylglycerol droplets forming mixed micelles.
pancreatic lipase on triacylglycerol leads to 2 fatty acids and monoacylglycerol.
what inhibits pancreatic lipase
orlistat
how are triacylglycerols transported? what do these particles contain?
in chylomicrons
contain triacylglycerol, phospholipids, cholesterol + esters, vitamins A/D/E/K
where are chylomicrons secreted
from mucosal cells in intestine into lymphatic system, then enter blood through thoracic duct.
what class are chylomicrons a member of
plasma lipoproteins
structure of chylomicrons
core of triacylglycerol and acyl-cholesterol (hydrophobic)
surrounded in hydrophilic components - phospholipids, cholesterol, apoproteins
half life of chylomicrons in the plasma?
~5mins
degradation process of chylomicrons?
collect apoprotein C-II which activates degradation enzyme lipoprotein lipase (endothelial cell surfaces).
this hydrolyses triacylglycerol to free fatty acids and glycerol.
free fatty acids taken up by cells.
glycerol remains in plasma and metabolised by liver.
chylomicrons converted to chylomicron remnants which are taken up by the liver.
what is the start point for synthesis of long chain fatty acids? what is the first reaction controlled by? what does it involve?
acetyl-CoA
first reaction controlled by acetyl-CoA carboxylase (important control point for synthesis and degradation). requires ATP and CO2 (from bicarbonate)
what is acetyl-CoA carboxylase inactivated by?
phosphorylated form = inactive
phosphorylation promoted by glucagon, AMP-activated protein kinase, long chain fatty acyl-CoA
what is acetyl-CoA carboxylase activated by?
dephosphorylated form = active
dephosphorylation promoted by insulin
fatty acid synthase complex structure, features?
multi-enzyme complex, 2 identical subunits
each subunit has 7 different activities.
converts acetyl-CoA to long chain fatty acids (16 carbon, saturated)
7 activities in fatty acid synthase complex?
priming
loading
condensation
two reductions
acyl transfer
reloading
hormonal control of triacylglycerol synthesis?
insulin - promotes glucose uptake, acetyl-CoA formation and exportation from mitochondria
glucagon - inhibits glucose conversion, inhibits acetyl-CoA carboxylase
malonyl-CoA features?
precursor for fatty acid synthesis
inhibitor of fatty acid oxidation
unsaturated fatty acids structure?
1 to 4 double bonds
some can be made, some are essential
fatty-acid desaturase system?
removal of 2 hydrogens (reduces O2 to H2O)
other oxygen atom reduced by reduced NAD
insertion of double bonds begins at carbon 9
why does essential fatty acid deficiency take a long time to develop?
large reservoir in the body
mobilisation of triacylglycerol in adipose tissue done by which enzyme? how is this hormonally controlled?
hormone-sensitive lipase hydrolyses triacylglycerol in adipose tissue
inhibited by insulin
promoted by adrenaline/glucagon/growth hormone
eventual product of triacylglycerol in adipose tissue?
glycerol and free fatty acids
features of fatty acids?
low solubility
capable of diffusing through biological membranes
what are fatty acids transported with?
fatty acids are transported bound to serum albumin
how do fatty acids enter cells?
via fatty acid transporters
how are fatty acids prevented from leaking back into the plasma once they’ve entered a cell?
attached to coenzyme A (large hydrophilic enzyme)
what do fatty acids become once they’ve entered the cell?
acyl-CoA (long chain fatty acids esterified onto coenzyme A)
