lipids synthesis Flashcards
how long can FA be made
up to 36 carbons can be made in vivo but they all originate from the same precursor- the C16 FA palmitate
where does palmiate synthesis take place
in the cytosol
what creates the palmitate FA
the single multifunctional enzyme
fatty acid synthase (FAS)
The synthesis of long-chained fatty acids
(C18 and higher) occurs where
in the endoplasmic
reticulum and mitochondria
The synthesis of long-chained saturated
fatty acids from palmitate requires:
– palmitoyl-CoA (aka “activated” palmitate)
– malonyl-CoA (endoplasmic reticulum) or
acetyl-CoA (mitochondria)
– NADH or NADPH, plus H +
– 4 individual enzymes (rather than one enzyme
as with palmitate synthesis)
what are the steps to fatty acyl Co-A elongation
- condensation
- reduction
- dehydration
- reductino
what enzyme does condensation step
fatty acid elongase
what enzyme does the first reduction step
B-keto acyl CoA reductase
what enzyme does the dehydratino step
B-hydroxy acyl CoA dehydrase
what enzyme does the second reduction
2 trans enoyl CoA reducatase
what is the final step of fatty acyl CoA elongation
The final step involves either the action of thioesterase on the elongated fatty acyl- CoA (liberating the new fatty acid and CoA-SH), or the further elongation or desaturation of the elongated fatty acyl- CoA
what enzyme carries out elongation of very long chained fatty acids
Elovl- previously termed fatty acid elongase, condense malonyl-CoA and acetyl-CoA with a fatty acyl-CoA
* To date, there are 7 Elovl’s
– Elovl1, Elovl2… Elovl7
how are the Elovl’s categorized
The Elovl’s are divided into three classes:
– Elongation of saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA):
– Elongation of polyunsaturated fatty acids
(PUFA):
– Elongation of specific fatty acids:
what carries our the Elongation of saturated fatty acids (SFA) and
monounsaturated fatty acids (MUFA):
Elovl1, Elovl3, and Elovl6
what carries out the Elongation of polyunsaturated fatty acids
(PUFA):
Elovl2 and Elovl4
what carries out the elongation of specific fatty acids
Elovl5 and Elovl7
what does the unsaturation of fatty acid require
the fatty acyl-CoA desaturases
what desaturases are there in mammals
– ∆5 desaturase
– ∆6 desaturase
– ∆9 desaturase or stearoyl-CoA desaturase
(SCD)
* 5 isozymes exist: SCD1, SCD2… SCD5
With very few exceptions, the desaturation
(or the introduction of a carbon-carbon
double bond by reduction) of a saturated
fatty acyl-CoA is introduced at the
9 th
carbon from the carboxylic acid (with the
carbon at C=O being #1)
where can insects desaturate sites
delta 5, 6, 9, 12, 15
wherecan lower plants desaturate fatty acids
delta 6, 9, 12, 15
where can animals desaturate fatty acids
delta 4, 5, 6, 9
where can plants desaturate fatty acids
delta 9, 12, 15
what are the essential fatty acids that cannot be syntheszed by mammals
Linoleate (18:2(∆9,12 ) or 18:2n6)
α-linolenate (18:3(∆9,12,15 ) or 18:3n-3)
how do plants generate omega 3 and omega 6 fatty acids
Plants have ∆12 and ∆15 desaturases
what can linoleate and a- linolenate be used for
Linoleate and α-linolenate can be used by
mammals to make key omega-3 and -6
lipids that exhibit many functions in vivo
functions of fatty acids
-stored as a component of TG, PL, an CE
-providing up to 14 ATP for every pair of carbons during
β-oxidaton
-have several beneficial and detrimental functions in vivo
how is the gene expression of SCD1 regulated
by the cellular levels of cholesterol and
polyunsaturated fatty acids (PUFA)
effect of high and low cholesterol on SCD1
High cholesterol levels inhibit the expression
of SCD1 whereas low cholesterol levels
increase the expression of SCD1
how does high levels of PUFA affect expression of SCD1
High PUFA levels also inhibits the expression
of SCD1
how is the mRNA of SCD1 regulated
by cellular fatty acids
effect of stearate and oleate on SCD1 transcript
Stearate and oleate have no effect on the
half-life of the SCD1 transcript (of 8h)
effect of arachidonate on SCD1
Arachidonate uniquely reduces the half-life of
the SCD1 transcript from 8h to 4h
starvation effect on SCD1 activity
diminished
uncotrolled type 1 diabetes effect on SCD1 activity
diminished
how is SCD1 expression altered with dietary sources of n-3 and n-6 fatty acids (as free FA or assocaited with TG/PL)
they repress the expression of SCD1
what are the dietary soruces of n-3 and n-6 FA that alter the expressino of SCD1
18:2n-6
18:3n-3
20:4n-6
20:5n-3
22:6n-6
how do diets with high carb levels affect SCD1 activity
induce it
how do diets with insulin administration affect SCD1 activity
induce it
how do diets rich in SFA affect SCD1 levels
elevate it
