Triacylglycerides and Phospholipids Flashcards
what is the structure of a TAG
glycerol esterified to 3 FAs. The FAs are generally not the same. FA#1 is usually saturated, #2 is unsaturated, and #3 can be either.
describe the storage of TAG
they hate water and cannot form micelles so form oily, anhydrous droplets in adipocytes
glycerol phosphate is the initial precursor for TAGs. where does it come from?
2 pathways:
1- in liver and adipose
using rxns of glycolysis, glucose is converted into DHAP. at that point, glycerol phosphate dehydrogenase converts DHAP into glycerol phosphate
2- only in liver
glycerol kinase converts free glycerol into glycerol phosphate
describe the synthesis of TAG from fatty acids and glycerol
2 steps:
- generation of fatty acid- CoA from fatty acid
the enzyme fatty acyl-CoA synthetase uses CoA and ATP to form fatty acid- CoA - a series of 4 rxns occurs as such
- first addition of fatty acyl- CoA
- second addition of fatty acyl -CoA
- removal of phosphate group
- third addition of fatty acyl- CoA
describe the different fates of TAG in the liver, intestines, and adipose
adipose- clustered in anhydrous droplets within the cytosol where it serves as a fat depot
liver- liver does not store fat. secretes it w/ cholesteryl esters, cholesterol, phospholipids, and proteins such as apolipoprotein B-100 in the form of very low density lipoproteins, VLDLs go into the blood and deliver endogenous lipids
intestines- package lipids in chylomycrons
what are the two classes of phospholipids
glycerophospolipids (glycerol backbone)
sphingolipids- (contain sphingosine)
discuss the structure of glycerophospholipids
all contain phosphatidic acid (diacylglycerol w/ phosphate group). different units, especially alcohols, can bind the phosphate group to create different relevant products
cardiolipin
constructed in mitochondria, two molecules of phosphatidic acid are esterified to a common glycerol through their phosphate groups. it forms an important part of the inner mitochondrial matrix
it is also the only glycerophospholipid known to be antigenic, as Abs against syphyllis will react with caridolipi
how is phosphatidic acid formed?
through the same pathway as TAG, except w/o the removal of the third phosphate group for another acyl ester
describe synthesis of glycerophospholipds
2 pathways
the combination is of diacylglycerol with an alcohol. the 2 mechanisms seperate is in which react is bound to CDP, which becomes the activated intermediate. they combine and release CMP
synthesis occurs in the smooth ER and are sent to the Golgi
sphingomyelin
3 carbon backbone
alcohol and fatty acid attached to 1 C
amine group with fatty acid attached to middle C
phosphorylcholine group attached to last C
a part of the PM w/ high affinity for cholesterol and an important part of myelin
ceramide
a part of sphingomyelin (w/o the phosphorylcholine) w/ two fates
- become sphingomyelin via attachment of phosphorylcholine
- C3 alcohol link with glucose or galactose and become precursor for phospholipids
describe the degradation of phosphoglycerides
done by phospholipases destroying the ester bonds
removal of the fatty acid from C1 or 2 creates a lysophosphoglyceride, which are substrates for lysophospholipases
phospholipases can cause the release of messengers (DAG and IP3) and also can selectively remove specific fatty acids for replacement with another fatty acid via a transferase
describe the degradation of sphingomyelin
done by sphingomyelinases to form ceramide, which is degraded by ceramidase into a FA and sphingosine
Niemann-Pick disease
lack of a sphingomyelinase means it cant be broken down. enlargement of liver and spleen and uncontrolled sphingomyelin deposits placed in CNS cause infant death in type 1. type 2 affects spleen liver lungs and bone marrow
more frequent in Ashkanzi jew population
