Fatty Acid Synthesis Flashcards

1
Q

Where are fatty acids synthesized?

A

Cytoplasm

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2
Q

What is the first step in FA synthesis?

A

Moving Acetyl CoA to the cytoplasm for FA synthesis

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3
Q

How is acetyl CoA moved across the mitochondrial membrane to the cytosol?

A

Acetyl CoA is condensed with Oxaloacetate to form citrate, which is transported across the membrane.

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4
Q

What is the function of ATP-citrate lyase?

A

Breaks citrate down into acetyl CoA and oxaloacetate in the cytosol

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5
Q

Where is NADPH synthesized for the synthesis of palmitate?

A

8 molecules are formed when 8 acetyl CoA are transported to the cytoplasm

Remaining 6 come from pentose phosphate pathway

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6
Q

What is the rate limiting step for fatty acid synthesis?

A

Formation of malonyl CoA

Catalyzed by Acetyl CoA carboxylase

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7
Q

What is the active structure of Acetyl-CoA carboxylase?

A

Active enzyme exists as filaments, monomers are inactive

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8
Q

How is Acetyl CoA carboxylase regulated by phosphorylation?

A

Inactivated via phosphorylation by AMP-activated protein kinase

Activated by dephosphorylation by protein phosphatase 2A.

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9
Q

What triggers phosphorylation of acetyl-CoA carboxylase?

A

Glucagon and Epinephrine

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10
Q

How does citrate influence the activity of acetyl-CoA carboxylase?

A

Allosterically activates it by facilitating the polymerization of inactive dimers into active filaments

Phosphorylation reduces sensitivity to stimulating effect of citrate

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11
Q

What molecule counteracts the stimulatory effect of citrate?

A

Palmitoyl CoA

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12
Q

How does insulin affect fatty acid synthesis?

A

Stimulates synthesis by stimulating dephosphorylation of acetyl-CoA carboxylase

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13
Q

What is adaptive control of Fatty Acid synthesis?

A

Fasting then feeding will increase acetyl CoA carboxylase activity, increasing fatty acid synthesis

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14
Q

Describe the structure of Fatty Acid Synthase.

A

Two identical chains folded into 3 domains joined by flexible regions

7 catalytic sites

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15
Q

What is the function of acyl carrier protein?

A

Carries the intermediates during FA synthesis

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16
Q

How is fatty acid synthesis initialized?

A

Acetyl CoA bonds to FA synthase

Provides the omega carbon for the fatty acid chain

17
Q

What provides the carbons for elongation of the fatty acid chain?

A

Malonyl CoA

18
Q

How many NADPH and ATP are required for the synthesis of Palmitate?

A

14 NADPH

7 ATP

19
Q

Where are the enzymes for elongation and desaturation of palmitate located?

A

Cytoplasmic face of the endoplasmic reticulum

20
Q

What enzymes introduce double bonds to unsaturate fatty acids?

A

ER mixed function oxidases

Three membrane bound enzymes catalyze the introduction of double bonds.

2 molecules of water are released

21
Q

What carbon is the limit for introducing double bonds in mammals?

A

Cannot desaturate beyond the delta-9 carbon

22
Q

What are eicosanoids derived from?

A

20C polyunsaturated fatty acids

23
Q

What are leukotrienes?

A

Derived from arachidonate, important in allergic reactions

24
Q

What is the site of aspirin activity?

A

Prostaglandin synthase

25
What are 6 functions of prostaglandins?
Stimulate inflammation Regulated blood flow to certain organs Control ion transport Modulate synaptic transmission Induce sleep Important in clotting
26
What are the sites of steroid action?
Phospholipase A2 - involved in synthesis of arachidonate Cyclooxygenase activity of COX
27
What is the function of Thromboxane A2?
Promotes clotting smooth muscle contraction
28
What is the function of Prostacyclin (PGI2)?
inhibits platelet aggregation and promotes vasodilation