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Biochemistry > Block 3 Fatty Acid Oxidation > Flashcards

Block 3 Fatty Acid Oxidation Flashcards

1
Q

What are fatty acids? Where are they found?

A

Carboxyl group + long hydrocarbon chain 4-24C; part of lipid molecule or complexed to carrier protein like albumin

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2
Q

What length are SC, MC, LC, VLC FAs? What happens with increasing chain length? What length are dietary and stored FAs?

A

SC: 2-4C, MC: 6-12C, LC: 14-20, VLC: <22
Decreased solubility, fluidity, increased melting point
16-18C (mix of sat, MU, PU)

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3
Q

What is 18:0 fatty acid?

A

Stearic acid (octadecanoic acid)

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4
Q

What is 18:1 d9?

A

Oleic acid (octadecenoic acid)

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5
Q

What is 18:2 d9,12?

A

Linoleic acid (octadecadienoic acid)

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6
Q

What is 18:3 d9,12,15?

A

Alpha-linolenic acid (octadecatrienoic acid)

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7
Q

What are the sources of FAs and how are is their energy used in peripheral tissues?

A

Fed state: dietary TGs to CMs stored
Fasted: TAG in adipose -> FA (gluc/epi) on albumin to be oxidized
Postprandial: TAG synth in liver -> carb exported on VLDL stored/oxidized

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8
Q

What is b-oxidation?

A

Major in mito (PUFA and sat, LC and MCFA, provides NADH and FADH2); peroxisomal (VLCFA)

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9
Q

What are alpha and omega oxidation?

A

A: peroxisomal pathway for branched chain FAs
O: microsomal pathway for detoxifying lipid molecules

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10
Q

What are the steps of FA ox?

A

Transport into cell, activation by FaCoA (cytosol), transport into mito (carnitine shuttle), B-ox to AcCoA

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11
Q

Where does AcCoA from beta oxidation go?

A

Fed state: oxidation in TCA

Fasted: in liver makes ketone bodies, then in peripheral tissues ketone -> AcCoA oxidized

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12
Q

What is a thiokinase?

A

Acyl-CoA synthase, specific to FA length; to esterify FA to CoA, ATP-dependent (2 ATP), on ER and OMM

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13
Q

What is a CPT?

A

Carnitine palmitoyl transferase, catalyzes transfer of FA between thiol of CoA and hydroxyl on carnitine to move FA across mito membrane

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14
Q

What is carnitine?

A

Can be synth in body, precursor trimethyllysine, essential in infants, in red meat and dairy, not soy

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15
Q

What are the 3 steps of carnitine-mediated transfer of FA into mito matrix?

A

1) CPT 1 transfers FA from CoA to OH on carnitine
2) Antiporter in IMM exchanges carnitine for acyl-carnitine
3) CPT2 in matrix transfers FA from carnitine to CoA

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16
Q

What is the main regulated step of FA transport? What does it?

A

FA entry into mito; malonyl-CoA (precursor for FA synth, from AcCoA by AcCoA carboxylase) inhibits CPT1

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17
Q

Where are the acyl-CoA DHs located?

A

All soluble in mito matrix but VLC bound to IMM

18
Q

What are the enzymes responsible for steps 2-4 of B-ox?

A

Enoyl-CoA hydrolase, b-hydroxyacyl-CoA DH, acyl-CoA acetyltransferase (thiolase); all soluble in matrix but membrane-bound in trifxl protein for long chain FAs

19
Q

What is the reaction for one round of B-ox?

A

Fatty acyl-CoA + FAD + NAD+ + HS-CoA -> fatty acyl-CoA (-2C) + FADH2 + NADH + H+ + AcCoA

20
Q

What are the products of B-ox if the FA has an even or odd number of carbons?

A

Even: butyryl-CoA -> 2 AcCoA
Odd: AcCoA + proprionyl-CoA (liver -> glucose synth)

21
Q

How is B-ox regulated by insulin and energy change?

A

Insulin increases FA synth in liver, increasing malonyl-CoA (1st step), inhibiting CPT1
Energy: high ATP = low ETC, increasing [NADH], inhibiting B-ox

22
Q

What is the main source of odd-chain FAs? Why?

A

Milk fat because cow GI bacteria makes C3 propionate

23
Q

How is propionyl-CoA metabolized?

A

Propionyl-CoA carboxylase + biotin -> 4C D-methylmalonyl-CoA + MM-CoA epimerase -> L-MM-CoA + MM-CoA mutase + B12 -> succinyl-CoA (TCA -> OAA -> glucose)

24
Q

How are VLCFA oxidized?

A

Within peroxisomes and mito; perox do not use carnitine, but export acyl-carnitines (product of COT/CAT)

25
Q

What are the products of perox B-ox?

A

FADH2, NADH, no ATP directly

26
Q

What are Zellweger syndrome and X-linked adrenoleuko-dystrophy?

A

Z: lack of functional peroxisomes
XALD: defect in perox ox of VLCFA

27
Q

What is alpha-oxidation?

A

Branched chain FA, in perox; chlorophyl -> phytanic acid (methyl on beta-C = no B-ox); alpha removes a C = substrate for B-ox

28
Q

What is Refsum disease?

A

Neurological damage from genetic deficit in alpha-oxidation and abnormal metabolites

29
Q

What is omega oxidation?

A

Ox of methyl C to dicarboxylic acid in microsomes, uses CytP450; to convert xenobiotics and FA metabolites (like PGs) to soluble compounds

30
Q

What does MCADD lead to?

A

Accumulated C8/10 FAs -> dicarboxylic acids by w-oxidation

31
Q

What are ketone bodies?

A

In fast, ox of FA incomplete b/c depletion OAA (gluconeo) so AcCoA can’t enter TCA, 4C acetoacetate and b-hydroxybutyrate released into blood

32
Q

When and where are ketones utilized?

A

Fasting: TCA active in mm, heart, brain; primary use in mm, brain if prolonged fast; can cross placenta to fetus and fetal brain

33
Q

How are ketones utilized in fast?

A

B-HB + DH -> acetoacetate + sucCoA-acetoacetate transferase -> acetoacetyl-CoA (OR: instead of sucCoA, ATP + CoASH -> aa-CoA + AMP + PPi) + thiolase -> 2 AcCoA

34
Q

What are the products of acetoacetate following DH or decarboxylation?

A

B-HB DH -> B-HB (reversible, major ketone in blood)

Spontaneous DC -> acetone (excreted)

35
Q

Why are children more prone to ketosis than adults? What are common causes?

A

More energy use/kg body mass, higher brain/liver ratio, liver glycogen stores depleted more rapidly; mild infections that may cause anorexia and vomiting

36
Q

What is a ketogenic diet? When is it recommended? What TGs are best for it?

A

High fat (3:1 lipid to carb cals) to reduce freq epileptic seizures, in kids with PD deficiency; MCFA more ketogenic than normal dietary C16-18 bc oxidized rather than stored in TAG or PM

37
Q

What might be affected by mutation to cause a B-ox disease?

A

PM FA transporter CD36, CPT1/2, AcCoA DH, hydroxyacyl-CoA DH (M/SCFA), medium chain b-ketothiolase, trifxl protein complex, ETF (ET flavoprotein)

38
Q

What are common symptoms of B-ox disease?

A

Hypoketotic hypoglycemia, fatty degeneration of liver, heart/sk mm defect, maternal preg complications, SIDS

39
Q

What is MCADD?

A

FA partially ox, C8/10 found in blood and urine, C8/10 dicarboxylic acids and acyl-carnitines; tx with diet & exogenous carnitine to replace losses

40
Q

What is systemic carnitine deficiency?

A

Cardiomyopathy, sk mm weakness, hepatomegaly, elevated liver enzymes; hypoketotic hypoglycemia; imparied ox LCFA (normal MCFA use); defect in OCTN-2 so kidney can’t reabsorb carnitine and mm can’t acc against gradient; tx carnitine and high carb/low fat diet

Biochemistry (17 decks)

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