Biosynthesis of Fatty Acids Flashcards
What is the starting material for fatty-acid synthesis?
Acetyl co-a (in mitochondria), which itself is mostly from pyruvate
True or false: acetyl co-a is only found in mitochondria.
False. Citrate from the TCA cycle can pass through the mitochondrial membranes into the cytosol. It is then broken down to oxaloacetate and acetyl co-a by ATP cirate lyase; the oxaloacetate passes back into the mitochondria once converted back to pyruvate (via malate).
In the cytosol, acetyl co-a gets converted to ___________ by acetyl co-a carboxylase.
malonyl co-a
Fatty acid synthase converts malonyl co-a to __________.
palmitate
Desaturation of palmitate is accomplished by ____________.
the ER
Both the mitochondria and ER can __________ palmitate.
elongate
In naming unsaturated fatty acids, the double bonds are named for ____________.
the carbon they start on; for instance, 20:2(5,8) means a 20-carbon chain with two double bonds that go from 5 to 6 and from 8 to 9
Why can’t people make linoleic acid and alpha-linoleic acid?
Because human cells lack enzymes to put double bonds from carbon 9 to the end of the chain.
What are three important uses for fatty acids?
- Compose the cell membrane
- Act as triglyceride storage
- Precursors for eicosanoids
______________ is the precursor to arachidonic acid.
Linoleic acid
Formation of malonyl co-a is stimulated by ____________ and inhibited by __________.
citrate (a sign of nutrient excess); long-chain fatty acyl co-a (the immediate downstream product)
____________ has many (seven) different activities.
Fatty acid synthase
The first two carbons in fatty acid synthesis are from ___________, while all subsequent carbons are from ____________.
acetyl co-a; malonyl co-a
NADPH is used in ______________.
the reducing steps of fatty acid synthesis
In addition to being produced in the hexose monophosphate shunt, NADPH can also be made by ____________.
NADH + NADP+ -> NAD+ NADPH
What things stimulate and inhibit fatty acid synthesis?
Stimulate:
- high carbohydrate levels leading to lots of acetyl co-a
- high insulin levels
Inhibit:
- high fat/low carb diets leading to increased cytosolic acyl co-a
- high glucagon levels
Insulin promotes the conversion of acetyl co-a to malonyl co-a by _______________.
dephosphorylating acetyl co-a carboxylase (via protein phosphatase)
Vmax directly correlates with ______________.
enzyme concentration
Almost all of the endogenous fatty acids are in the ______ configuration.
cis
High levels of ATP lead to increased fatty-acid synthesis by what mechanism?
ATP inhibits isocitrate dehydrogenase, leading to accumulation of citrate.
Fatty acid synthase ultimately produces __________.
palmitic acid (a 16-carbon molecule)
What enzyme is activated when polymerized and deactivated when depolymerized?
Acetyl co-a carboxylase
What enzyme synthesizes triglyceride?
Acyltransferase
Why does alcohol consumption promote fatty acid synthesis?
Alcohol is metabolized to acetyl co-a
The rate-limiting enzyme in fatty acid synthesis is _____________.
acetyl co-a carboxylase
The family of enzymes that elongate fatty acids is called ______________.
fatty acid elongase
What do mixed function oxidases do?
Introduce double bonds
Fatty acids must be ____________ before being activated to triglycerides.
activated by binding co-a
