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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
fatty acid synthesis rxn 1
acetyl-CoA to malonyl-CoA | enzyme: acetyl-CoA carboxylase
26
acetyl-CoA carboxylase cofactors
ATP Biotin Carbon dioxide
27
rate-limiting step
acetyl-CoA carboxylase
28
2 types of regulation of acetyl-CoA carboxylase
hormonal and allosteric regulation
29
hormonal regulation of acetyl-CoA carboxylase
insulin (removes) and glucagon (adds) a phosphate group to acetyl-CoA carboxylase
30
fed state
insulin activates phosphatase 2 which removes phosphate group from acetyl-CoA carboxylase, increasing activity
31
fasted state
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
32
allosteric regulation
molecule increases or decreases activity of an enzyme by binding on a site different to where the substrate binds
33
citrate and acetyl-CoA carboxylase
citrate allosterically increases activity of acetyl-CoA carboxylase
34
fatty acids and acetyl-CoA carboxylase
fatty acids allosterically inhibit it
35
fatty acid synthase complex
has 2 binding domains on each end | 1 has ACP, one has exposed Cysteine
36
ACP
acetyl-CoAs and malonyl-CoAs bind inititally
37
cysteine site
where they hop on growing lipid
38
acetyl-CoA ACP transacylase
removes CoA from acetyl-CoA and attaches acetate (2Cs) to ACP which hops onto Cysteine residue enzyme: acetyl-CoA ACP transacylase
39
malonyl-CoA ACP transacylase
removes CoA from malonyl-CoA and then attaches malonate (3Cs) at ACP (acetate is still on Cysteine site)
40
3 ketoacyl-ACP synthase
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
1 cycle, what happens
1 acetyl-CoA to 1 malonyl-CoA | 2 NADPH needed
42
to make a 16 carbon palmitoyl-CoA we need...
8 acetyl-CoA | 14 NADPH
43
where are fatty acids stored
in adipocytes and liver cells as TAGs
44
eicosanoids
locally acting hormones
45
what are eicosanoids derived from?
C20 fatty acids, like arachidonic acid
46
what do eicosanoids mediate?
inflammation, pain, fever, blood pressure, reproduction, blood clotting, sleep/wake cycle
47
where do eicosanoids act?
in the tissue they are made | they bind to GCPRs
48
arachidonic acid
the most prevalent eicosanoid precursor
49
what is arachidonic acid synthesized from?
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
different classes of eicosanoids
prostaglandins, prostacyclins, thromboxanes, and leukotrienes
51
what are all prostaglandins made from?
PGH2 | prostaglandins respond to infection/inflammation
52
NSAIDS
block synthesis of PGH2 block fever, pain block COX prevent binding of arachadonic acid
53
how does prostaglandin work?
it's made in response to allergy, but overproduction can cause anaphylactic shock
54
difference between fatty acid synthesis and beta-oxidation?
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
fatty acid chains are made by...
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
what does it take to generate palmitate?
acetyl-CoA 7 malonyl-CoA (includes acetyl-CoA, CO2, ATP) 14 NADPH
57
source of 2 carbon units during fatty acid synthesis?
malonyl-CoA
58
how is malonyl-CoA produced?
by acetyl-CoA carboxylase
59
acetyl-CoA carboxylase
contains biotin | biotin picks up carboxyl units from its biotin carboxylase subunit and transfers it to acetyl-CoA
60
acetyl-CoA carboxylase regulation
inhibited by palmitoyl-CoA and activated by citrate | BOTH allosteric
61
acetyl-CoA carboxylase regulation pt. 2
more active when not phosphorylated less active when phosphorylated
62
fatty acid synthase
1. MAT 2. KS 3. KR 4. DH 5. ER 6. TE 1+2 have condensing activities 3-6 have modifying activities
63
fatty acid synthesis rxn 1
acetyl group of 1 acetyl-CoA is transferred to ACP and next transferred to a cysteine sulfur group in KS enzyme
64
fatty acid synthesis rxn 2
malonyl group of malonyl-CoA is transferred to newly opened ACP site
65
fatty acid synthesis rxn 3
condensation of both 2 carbon units is driven by decarboxylation of malonyl-CoA (this happens at ACP site)
66
fatty acid synthesis rxn 4
4 carbon unit is reduced, dehydrated, and further reduced
67
fatty acid synthesis rxn 5
processed 4-carbon unit is transferred to cysteine sulfur group in KS new malonyl group binds open ACP site
68
fatty acid synthesis rxn 6
thioesterase (TE) releases palmitate in final rxn
69
how do we form additional fatty acids?
after release of palmitate via TE activity of FAS, elongation reactions and/or desaturation reactions may produce additional forms of fatty acids
70
fatty acid elongation
occurs in mito or ER | occurs by condensation with malonyl-CoA
71
unsaturated fatty acids
produced by terminal desaturases | double bonds in unsaturated fatty acids are omega or delta FAs
72
what fatty acids are essential?
omega3 and omega6 FA | essential means we need them but come from our diets
73
what are omega6 FA precursors of?
eicosanoids
74
what are omega3 FA precursors of?
linoleic acid or linolenic acid
75
what are linoleic acid or linolenic acid precursors of?
arachidonic acid, EPA, DHA
76
what happens to free fatty acids?
they don't stay in cytosol! | they rapidly esterify and move in TAGs or membrane lipids
77
membrane lipids
glycerolipids and sphingolipids
78
glycerolipids
(DAG) can be modified by carbohydrates or phosphates
79
sphingolipids
(ceramide) may be modified by carbs or phosphates
80
precursor for glycerophospholipids?
phosphatidic acid
81
what are sphingolipids made from?
ceramide! | sphingomyelin is major sphingophospholipid
82
why do we need sphingolipids?
neuronal function!
83
sphingolipid degradation
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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