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BIOC 3300 > Week 4 => Fatty acid biosynthesis, modification, and regulating oxidation > Flashcards

Week 4 => Fatty acid biosynthesis, modification, and regulating oxidation Flashcards

1
Q

Where are enzymes for fatty acid synthesis found?

A

The cytosol

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2
Q

How does acetyl-CoA generated in the mitochondrial matric get transported to the cytoplam?

A

Transported indirectly in the form of citrate and released int he cytoplasm by the enzyme ATP citrate lyase

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3
Q

What metabolite production would cause a futile cycle with fatty acid synthesis?

A

beta-oxidation of fatty acyl-carnitine to acetyl-CoA

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4
Q

How many Acetyl-CoA does one Acetate produce?

A

8

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5
Q

What are cellular functions C16 fatty acid-palmitate contribute to?

A
  • Post-translational modifications
  • Membrane biogenesis
  • Cell signaling and second messengers
  • Energy storage
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6
Q

Example of molecule what contributed to post-translational modifications?

A

Protein acylation

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7
Q

Example of molecule what contributed to membrane biogenesis?

A

Phospholipids and sphingolipids

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8
Q

Example of molecule what contributed to cell signaling & second messengers?

A

Eicosanoids

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9
Q

Example of molecule what contributed to energy storage?

A

Triacylglycerol

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10
Q

Function of ATP citrate lyase?

A

Releases acetyl-CoA (from citrate) for fatty acid and cholesterol synthesis

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11
Q

Due to fatty acyl groups have limited aqueous solubility what form are they found as to involve aqueous solubility and serve as reactive forms in biosynthetic reactions?

A

Thioesters or acyl carrier proteins (ACP) or of coenzyme A (CoA)

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12
Q

On phopshopantetheine groups what do the free SH- groups on the cysteamine segment form?

A

Free -SH groups from thioester linkages to FAs

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13
Q

What is the source of malonyl-CoA carboxyl group (COO-) on Malonyl-CoA?

A

Bicarbonate

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14
Q

Enzyme for synthesis of Malonyl-CoA

A

Catalyzed by acetyl-CoA carboxylase (ACC1 and ACC2 isoforms)

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15
Q

ACC1 location and predominant function?

A

ACC1 predominates in fatty acid synthesizing tissues (Adipose and liver) and catalyzes rate-limiting step

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16
Q

What does phosphorylation of ACC1 do?

A

Blocks polymerization and inactivates the enzyme

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17
Q

ACC2 location and predominant function?

A

ACC2 is present in fatty acid oxidative tissues (muscle) where it associates with mitochondria and inhibits beta-oxidation by producing malonyl-CoA

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18
Q

ACC 3 functionalities

A

a) biotin carrier
b) biotin carboxylase
c) transcarboxylase

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19
Q

How does biotin carboxylase work?

A

Activates CO2 (from bicarbonate) by attaching it to ring nitrogen of biotin on the carrier

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20
Q

How does Transcarboxylase work?

A

Activity transfers the CO2 from biotin to acetyl-CoA, generating malonyl-CoA

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21
Q

Fatty acid synthesis is catalyzed by ____

A

Multi-enzyme Fatty Acid Synthase (FAS) complexes

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22
Q

FASI structure

A

Mammalian FASI is single polypeptide containing all the enzymatic activities

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23
Q

FASII structure

A

Prokaryotic FASII is a dissociated complex of individual enzymes and ACP

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24
Q

Products of FASII

A

The 16-carbon fatty acid palmitate, but intermediates in synthesis can be released

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25
Q

Products of FASI

A

The 16-carbon fatty acid palmitate but no intermediates released

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26
Q

What regulates FASI

A

Substrate availability and transcriptional mechanisms involving sterol-regulatory element binding protein (SREBP)

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27
Q

Where does fatty acid synthesis occur?

A

Occurs in the cytoplasm in eukaryotic cells. Also a minor fatty acid synthesis pathway in mitochondria

28
Q

Generally how does fatty acid synthesis occur?

A

Synthesis involves series of 2-carbon condensation reactions using malonyl-CoA to extend an acyl chain

29
Q

What are the 4 repeating reactions in FASI?

A

1) Condensation
2) Reduction
3) Dehydration
4) Reduction

30
Q

What is the enzyme in 1st reduction step of FASI reactions?

A

beta-ketoacyl-ACP reductase

31
Q

What is the enzyme in dehydration step of FASI reactions?

A

beta-hydroxyacyl-ACP-dehydrogenase

32
Q

What is the enzyme in 2nd reduction step of FASI reactions?

A

Enoyl-ACP-reductase

33
Q

what is the product in the first round of the FASI cycle?

A

C4 Butyryl

34
Q

How many cycles is required to elongate fatty acid to 16 carbon palmitate?

A

7 cycles

35
Q

What occurs after the formation of palmitate?

A

The palmitate is cleaved by thioesterase (TR) activity in FASI. Palmitate is immediately converted to palmitoyl-CoA by a fatty acyl-CoA synthase

36
Q

List parts of FASII loose complex of 6 different polypeptides with enzyme activities plus ACP

A

1) Malonyl-CoA-ACP transferase (MT/FabD)
2) beta-Ketoacyl-ACP synthase (KS/FabH, FABH+F)
3) beta-Ketoacyl-ACP reductase (FR/FabG)
4) beta-hydroxyacyl-ACP dehydrase (DH/FabZ+A)
5) Enoyl-ACP reductase (ER/FabI)

37
Q

Sources of NADPH for fatty acid synthesis

A
  • Oxidation of malate to pyruvate
  • PPP oxidative phase (when producing P-phosphogluconate and Ribulose 5-phosphate)
38
Q

Hormonal regulation of Fatty acids

A
  • Insulin => promotes fatty acid synthesis
  • Glucagon/epinephrine => decrease fatty acid synthesis
39
Q

Allosteric regulation of fatty acid biosynthesis

A
  • Citrate is an allosteric activator of ACC1, promoting malonyl-CoA synthesis
  • Product (palmitoyl-CoA) promotes depolymerization and inactivation
  • ACC1 is inhibited by phosphorylation by AMP-dependent Kinase (turn off ATP consuming biosynthesis pathways when ATO is scarce)
40
Q

Δ Nomenclature of fatty acids

A

Position of the double bond is from the carboxyl end of the acyl chain

41
Q

To fully describe fatty acids which nomenclature should be used?

A

Both nomenclatures

42
Q

n- or ω- Nomenclature

A

Identifies only the first double bond from the methyl end of the acyl chain

43
Q

What are the two genomic configuration of double bonds?

A

Cis or trans

44
Q

What does increasing chain length effect?

A

Increases melting point (mp)

45
Q

How do double bonds effect melting point?

A

For a given chain length, increasing number of double bonds decreases melting point (mp)

46
Q

Beyond what carbon can animals not introduce double bonds?

A

C10

47
Q

What are essential fatty acids series

A

n-3 and n-6 series (must be acquired in the diet)

48
Q

What increments does fatty acid elongation occur?

A

2-carbon increments

49
Q

What can fatty acid desaturation occur by?

A

The Δ9 desaturase, Δ6 desaturase, or Δ5 desaturase

50
Q

What does fatty acids desaturation introduce?

A

cis-double bonds

51
Q

What is Δ9 desaturase expression stimulated by?

A

Insulin

52
Q

What does Δ9 desaturase require?

A

3 membrane proteins, O2 and NAD(P)H and uses fatty acyl-CoA as substrate

53
Q

In plants where is the fatty acid desaturated?

A

The fatty acid at the sn-2 position is desaturated

54
Q

What desaturases do plants use?

A

Δ6, Δ9, Δ12, and Δ15

55
Q

What do plant desaturases use as substrates?

A

Phospholipids

56
Q

What do animal desaturases use as subtrate?

A

Fatty acetyl-CoA

57
Q

Where is the majority of elongation acitivity?

A

ER

58
Q

First step of fatty acid elongation

A

Condensation of the long chain acyl-CoA substrate with malonyl-CoA, catalyzed by one of two condensing enzymes, specific for either saturated or unsaturated acyl substrates

59
Q

Second step of fatty acid elongation

A

the beta-ketoacyl-CoA is reduced by NADPH, dehydrated and the enoyl-CoA reduced again by NADPH to give a fatty acid two carbons longer than the original substrate.

60
Q

Mitochondrial fatty acid elongation

A
  • uses acetyl-CoA instead of malonyl-CoA as source of 2C units
  • Pathway for synthesis of lipoic acid from C8 fatty acid
61
Q

Eicosanoids

A
  • A class of lipid compounds with potent physiological activities (signaling lipids)
  • include prostaglandins, thromboxane, and leukotrienes
  • action confined to local environment, and catalyzed extremely rapidly
  • all originate from C20 ‘eicosanoid acids’, particularly arachidonic acid
62
Q

Eicosanoid biosynthesis

A

After release from phospholipids, arachidonic acid undergoes modification in the cyclo-oxygenase (cyclic) or the lipoxygenase (linear) pathways to form active prostaglandins or leukotrienes, respectively

63
Q

What does Eicosanoids signal through?

A

G-protein coupled receptors (GPCRs)

64
Q

Cyclo-oxygenase (COX) inhibitors

A

Aspirin (acetylsalicylic acid) or ibuprofen reduces prostaglandin levels (which mediate pain sensation) and thromboxane levels (which mediates blood blotting)

65
Q

Non-steroidal anti-inflammatory drugs (NSAIDs)

A
  • Mimic the substrate or a reaction intermediate for COX1 and 2
  • COX1 is constitutive enzyme with homeostatic functions while COX2 is induced by inflammations

BIOC 3300 (11 decks)

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