Fatty acids and Membrane phospholipids biosynthesis Flashcards
seeing as the carbons from an acetyl-coA are the ones used to elongate a fatty acid, what brings the acetyl into the cytosol?
the tricarboxylate transport system
the initiation of fatty acid synthesis takes place by?
the carboxylation of acetyl-coA to generate malonyl-coA
fatty acid synthesis carries out ? rxns at a time. It lengthens a fatty acid ? carbons at a time
7, 2
elongation and desaturation of Free fatty acids requires which enzymes?
elongases and desaturases
triacylglycerol are synthesized from ?
glycerol and fatty acids
fatty acid oxidation occurs where? Has which carrier group? Has what as an electron acceptor?
in the mitochondria. CoA as a carrier. FAD, NAD+ as acceptors.
what is the tricarboxylate transport system?
is it a citrate-malate-pyruvate shuttle. That provides cytosolic Acetyl -CoA and NADPH for fatty acid synthesis
what at the 3 sources of acetyl-coA
amino acid degradation (makes cytosolic). Fatty acid oxidation (makes mitochondrial). Glycolysis (cytosolic pyruvate) which is converted to acetyl-coA in mitochondria
how does the mitochondrial acetyl-coA enter the cytosol?
as citrate
How is citrate converted into pyruvate?
citrate + ATP citrate lyase = Oxaloacetate. +malate dehydrogenase = malate. + Malic enzyme = pyruvate
what is the Acetyl- carboxylase reaction?
It needs an ATP, a bicoarbonate ion, a Biotin enzyme
ATP is hydrolysed, the energy released form here is used to transfer the CO2 from bicarbonate to biotin.
This CO2 is then moved to acetyl-coA .
and this has formed malonyl-coA
acetyl-coA carboxylase, is inhibited by, and is activated by?
it is activated by citrate.
it is inhibited from long chain fatty acid
malonyl-coA inhibits
carnitine palmitoyl transferase I, which is a mitochondrial enzyme
explain the ACC hormones control. PKA
PKA senses CMP levels (controlled by glucagon levels). It can phosphorylate the carboxylase making it less sensitive to allosteric control
explain the ACC hormones control. AMP dependant kinase?
senses ATP/ADP levels in cells. Can phosphorylate carboxylate making it less sensitive
explain the ACC hormones control. protein phosphate 2A
dephosphorylation carboxylate making it more active
what’s are the steps of biosynthesis of fatty acids
loading, condensation, reduction and dehydration, elongation, unload
what is the loading step
has a malonyl/acetyl-transferase MAT. We load the acetyl group from acetyl-coA from the ACP. Then we load a malonate group from the malonyl-coA enzyme to the ACP. IN the end we have an acetyl group on the cysteine residue of FAS , and a malonate group on the ACP site of FAS. A coA is released
explain the condensation reactive
The decarboxylation of the malonate group, that allows the nucleophilic attack on the thioester bond between the acetyl group on the cysteine residue on FAS .it is done by beta-ketoacyl-ACP synthase. It generates acetoacetyl-ACP . CO2 is released
explain the reduction and dehydration steps
3: we reduce the ketone function of acetoacetyl-ACP by ACP reductase, and form hydroxybutyryl-ACP .
4: we have a dehydration reaction done by hydroxyacyl-ACP dehydrogenase, to form butenoyl-ACP
5: we have to make the double bond a single bond this is done by enoyl-ACP reductase, this forms butyryl ACP
butyryl-ACP becomes?
palmitoyl-ACP after 7 rxns cycles. Then it gets hydrolysed by palmitoyl-thioesterase. Then forms palmitate
list the domains of fatty acid synthase
ketoacyl synthase, malonyl synthase, dehydrase, enoyl reductase, ketoacyl reductase, thioesterase
what are desaturases?
are enzyme that form a double bond. Mammals only have C9/6/4/5 fatty acyl-coA desaturases. This means that a C9,12 acid is obtained by the diet and not by the body. They need the energy of NADHP. go to slide 26
how are dietary triacylglyerols turned into triacylglycerols for the body
they are acted upon by lipases, monoacylglycerol acyltransferase, diacylglycerol acyltransferase, and 2 coA groups are released (from the enzymes)
sphingolipids are synthesized from?
palmitoyl-coA and serine
prostaglandin synthesis from arachidonate is blocked by?
drugs
what forms the myelin sheath?
sphingomyelin
gangliosides are used for
brain neuron transmission
tay sachs disease is caused by?
malfunction in hexoaminidase A
