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Biochemistry 2 > Fatty acid synthesis > Flashcards

Fatty acid synthesis Flashcards

1
Q

different forms of lipids

A

cholesterol, glycerol, phospholipids, fatty acids

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2
Q

fatty acids

A

simplest form of lipids

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3
Q

triacylglycerides (TAGs)

A

3 fatty acids connected to glycerol

storage form!

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4
Q

short and medium chain fatty acids

A

come from diet

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5
Q

long chain fatty acids

A

synthesized by liver and fat cells

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6
Q

how are long chain fatty acids synthesized?

A

combining lots of 2 carbon molecules (acetyl-CoA) into palmitoyl-CoA (single chain 16 carbon molecule

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7
Q

use of plamitoyl-CoA

A

use to synthesize even longer fatty acids

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8
Q

to create palmitoyl-CoA where do atoms come from?

A

acetyl-CoA provides carbon atoms

NADPH provides hydrogen atoms

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9
Q

where do we get acetyl-CoA for fatty acid synthesis

A

carbohydrate metabolism (mainly glucose)

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10
Q

after a starchy meal…

A

increase in glucose, pancreas releases insulin, cells take in glucose

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11
Q

inside cells…

A

glucose enters glycolysis, yields 2 pyruvate and ATP

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12
Q

pyruvate goes to…

A

mitochondria after pyruvate dehydrogenase converts it to acetyl-CoA

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13
Q

acetyl-CoA goes to…

A

CAC where it combines with oxaloacetate to form citrate

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14
Q

citrate goes to…

A

ETC to form ATP

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15
Q

more glucose =

A

more ATP

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16
Q

when CAC enzymes are inhibited, what do we use acetyl-CoA for?

A

fatty acid synthesis

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17
Q

where are enzymes for fatty acid synthesis found?

A

in the cytoplasm

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18
Q

how does acetyl-CoA get from mitochondria to cytoplasm?

A

acetyl-CoA combines with oxaloacetate to form citrate (just like in CAC)
happens when ATP is high

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19
Q

once in cytoplasm,

A

citrate lyase cleaves citrate into oxaloacetate and acetyl-CoA
citrate shuttle!

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20
Q

citrate-malate shuttle…what does oxaloacetate do once in cytoplasm?

A

goes back to mitochondria to combine with the next acetyl-CoA
malic enzyme converts oxaloacetate to pyruvate (so it can cross to mito)
NADP+ to NADPH

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21
Q

once back in mitochondria, pyruvate…

A

is converted back into oxaloacetate by pyruvate carboxylase

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22
Q

what increases pyruvate carboxylase activity?

A

acetyl-CoA!

makes oxaloacetate more available

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23
Q

what provides hydrogens for fatty acid synthesis?

A

some comes from NADPH produced by malic enzyme

the rest comes from metabolism of excess glucose in PPP

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24
Q

fatty acid synthesis overview

A

acetyl-CoA to palmitoyl-CoA

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25
Q

fatty acid synthesis rxn 1

A

acetyl-CoA to malonyl-CoA

enzyme: acetyl-CoA carboxylase

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26
Q

acetyl-CoA carboxylase cofactors

A

ATP
Biotin
Carbon dioxide

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27
Q

rate-limiting step

A

acetyl-CoA carboxylase

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28
Q

2 types of regulation of acetyl-CoA carboxylase

A

hormonal and allosteric regulation

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29
Q

hormonal regulation of acetyl-CoA carboxylase

A

insulin (removes) and glucagon (adds) a phosphate group to acetyl-CoA carboxylase

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30
Q

fed state

A

insulin activates phosphatase 2 which removes phosphate group from acetyl-CoA carboxylase, increasing activity

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31
Q

fasted state

A

glucagon activates AMP-dependent kinase, adds phosphate group to acetyl-CoA carboxylase, decreasing activity
we want to use fatty acids for energy, not build them

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32
Q

allosteric regulation

A

molecule increases or decreases activity of an enzyme by binding on a site different to where the substrate binds

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33
Q

citrate and acetyl-CoA carboxylase

A

citrate allosterically increases activity of acetyl-CoA carboxylase

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34
Q

fatty acids and acetyl-CoA carboxylase

A

fatty acids allosterically inhibit it

35
Q

fatty acid synthase complex

A

has 2 binding domains on each end

1 has ACP, one has exposed Cysteine

36
Q

ACP

A

acetyl-CoAs and malonyl-CoAs bind inititally

37
Q

cysteine site

A

where they hop on growing lipid

38
Q

acetyl-CoA ACP transacylase

A

removes CoA from acetyl-CoA and attaches acetate (2Cs) to ACP which hops onto Cysteine residue
enzyme: acetyl-CoA ACP transacylase

39
Q

malonyl-CoA ACP transacylase

A

removes CoA from malonyl-CoA and then attaches malonate (3Cs) at ACP (acetate is still on Cysteine site)

40
Q

3 ketoacyl-ACP synthase

A

1) cuts off carbon that acetyl-CoA transacylase added and releases it as CO2 (leaves behind 2 carbon acetate
* required NADPH to NADP+
2) moves acetate from ACP to Cysteine site to make 4 carbon fatty acid chain
* requires NADPH to NADP+

41
Q

1 cycle, what happens

A

1 acetyl-CoA to 1 malonyl-CoA

2 NADPH needed

42
Q

to make a 16 carbon palmitoyl-CoA we need…

A

8 acetyl-CoA

14 NADPH

43
Q

where are fatty acids stored

A

in adipocytes and liver cells as TAGs

44
Q

eicosanoids

A

locally acting hormones

45
Q

what are eicosanoids derived from?

A

C20 fatty acids, like arachidonic acid

46
Q

what do eicosanoids mediate?

A

inflammation, pain, fever, blood pressure, reproduction, blood clotting, sleep/wake cycle

47
Q

where do eicosanoids act?

A

in the tissue they are made

they bind to GCPRs

48
Q

arachidonic acid

A

the most prevalent eicosanoid precursor

49
Q

what is arachidonic acid synthesized from?

A

linoleic acid, an omega6 fatty acid
arachidonic acid is at C2 position of phosphoglycerolipids. It must be released from phospholipids to be converted to the relevant eicosanoid

50
Q

different classes of eicosanoids

A

prostaglandins, prostacyclins, thromboxanes, and leukotrienes

51
Q

what are all prostaglandins made from?

A

PGH2

prostaglandins respond to infection/inflammation

52
Q

NSAIDS

A

block synthesis of PGH2
block fever, pain
block COX
prevent binding of arachadonic acid

53
Q

how does prostaglandin work?

A

it’s made in response to allergy, but overproduction can cause anaphylactic shock

54
Q

difference between fatty acid synthesis and beta-oxidation?

A

1) intermediates in fatty acid synthesis are covalently linked to sulfhydryl groups of ACP (acyl carrier proteins)
2) fatty acid synthesis occurs in cytosol
3) fatty acid synthase (FAS) is only protein in synthesis (it has many enzymatic activities)
4) synthesis uses NADP+/NADPH as co-enzyme for REDOX rxns

55
Q

fatty acid chains are made by…

A

1) acetate units activated by formation of malonyl-CoA
2) addition of 2 carbon units to growing chain is driven by decarboxylation of malonyl-CoA
3) iterative elongation until palmitate (16C)

56
Q

what does it take to generate palmitate?

A

acetyl-CoA
7 malonyl-CoA (includes acetyl-CoA, CO2, ATP)
14 NADPH

57
Q

source of 2 carbon units during fatty acid synthesis?

A

malonyl-CoA

58
Q

how is malonyl-CoA produced?

A

by acetyl-CoA carboxylase

59
Q

acetyl-CoA carboxylase

A

contains biotin

biotin picks up carboxyl units from its biotin carboxylase subunit and transfers it to acetyl-CoA

60
Q

acetyl-CoA carboxylase regulation

A

inhibited by palmitoyl-CoA and activated by citrate

BOTH allosteric

61
Q

acetyl-CoA carboxylase regulation pt. 2

A

more active when not phosphorylated

less active when phosphorylated

62
Q

fatty acid synthase

A
  1. MAT
  2. KS
  3. KR
  4. DH
  5. ER
  6. TE

1+2 have condensing activities
3-6 have modifying activities

63
Q

fatty acid synthesis rxn 1

A

acetyl group of 1 acetyl-CoA is transferred to ACP and next transferred to a cysteine sulfur group in KS enzyme

64
Q

fatty acid synthesis rxn 2

A

malonyl group of malonyl-CoA is transferred to newly opened ACP site

65
Q

fatty acid synthesis rxn 3

A

condensation of both 2 carbon units is driven by decarboxylation of malonyl-CoA (this happens at ACP site)

66
Q

fatty acid synthesis rxn 4

A

4 carbon unit is reduced, dehydrated, and further reduced

67
Q

fatty acid synthesis rxn 5

A

processed 4-carbon unit is transferred to cysteine sulfur group in KS
new malonyl group binds open ACP site

68
Q

fatty acid synthesis rxn 6

A

thioesterase (TE) releases palmitate in final rxn

69
Q

how do we form additional fatty acids?

A

after release of palmitate via TE activity of FAS, elongation reactions and/or desaturation reactions may produce additional forms of fatty acids

70
Q

fatty acid elongation

A

occurs in mito or ER

occurs by condensation with malonyl-CoA

71
Q

unsaturated fatty acids

A

produced by terminal desaturases

double bonds in unsaturated fatty acids are omega or delta FAs

72
Q

what fatty acids are essential?

A

omega3 and omega6 FA

essential means we need them but come from our diets

73
Q

what are omega6 FA precursors of?

A

eicosanoids

74
Q

what are omega3 FA precursors of?

A

linoleic acid or linolenic acid

75
Q

what are linoleic acid or linolenic acid precursors of?

A

arachidonic acid, EPA, DHA

76
Q

what happens to free fatty acids?

A

they don’t stay in cytosol!

they rapidly esterify and move in TAGs or membrane lipids

77
Q

membrane lipids

A

glycerolipids and sphingolipids

78
Q

glycerolipids

A

(DAG) can be modified by carbohydrates or phosphates

79
Q

sphingolipids

A

(ceramide) may be modified by carbs or phosphates

80
Q

precursor for glycerophospholipids?

A

phosphatidic acid

81
Q

what are sphingolipids made from?

A

ceramide!

sphingomyelin is major sphingophospholipid

82
Q

why do we need sphingolipids?

A

neuronal function!

83
Q

sphingolipid degradation

A

in lysosomes
absence of enzyme that degrades sphingolipids leads to toxic build up of intermediates (leads to progressive defects in neuronal function)

Biochemistry 2 (32 decks)

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