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MCG > SYLLABUS 20: Amino Acid Catabolism > Flashcards

SYLLABUS 20: Amino Acid Catabolism Flashcards

1
Q

when does amino acid catabolism occur?

A

when aa are in excess, in positive nitrogen balance, and you’re taking in more protein than need to replace body protein or make compounds

once body has enough aa to synthesize new protein & make nitrogenous molecules, start breaking down excess aa in diet

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2
Q

how are aa removed from the body

A

only via break down to other products, as there’s no storage form of aa

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3
Q

what tissues degrade excess aa?

A

all tissues, but especially liver and muscle

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4
Q

what do aa break down become?

A

**C products: **

acetyl CoA

acetoacetate

pyruvate

TCA cycle intermediates- OAA, aKG, succinyl CoA, fumarate

amino groups become urea

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5
Q

what are glucogeninc aa?

A

amino acids that produce pyruvate or any of the 4 TCA cycle intermediates, OAA, succinyl CoA, fumarate, aKG

aka aa that break down to anything else

includes all aa except for leucine, and to a large extent lysine

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6
Q

what are ketogenic aa?

A

aas that produce acetyl CoA and acetoacetate

leucine, lysine, phenylalanine, tyrosine, isoleucine, tryptophan

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7
Q

which aa are both glucogenic and ketogenic?

A

phenylalanine, tyrosine, isoleucine, tryptophan

b/c when break down, produce either pyruvate or a TCA cycle intermediate as well as acetyl CoA or acetoacetate

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8
Q

what are the C3 family of aa? what do they break down to?

A

alanine, serine, glycine, cysteine, tryptophan

break down to pyruvate

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9
Q

how does alanine break down

A

becomes pyruvate via GPT transamination rxn:

Ala + aKG -> Pyr + GLUT

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10
Q

how does tryptophan break down

A

its side chain is released as alanine during break down

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11
Q

how does cysteine break down?

bio importances of this?

A

cysteine loses its SH group, eventually forming sulfate + pyruvate

sulfate is important in:

  1. biochemical conjugation reactions w/ drugs
  2. in interacting w/ estrogens (estradiol sufate)
  3. formation of cell surface and joint biochemicals such as chondroitin and hyaluronic acid sulfates
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12
Q

how does glycine break down?

A

becomes serine via serine transhydroxymethylase rxn, and Ser -> Pyruvate

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13
Q

how does serine break down?

A

serine can be dehydrated to pyruvate by serine dehydratase

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14
Q

what are the C4 family of aa?

A

aspartate and asparagine

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15
Q

how is aspartate broken down?

A

Aspartate -> OAA via GOT transaminase reaction

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16
Q

how is asparagine broken down?

A

Asparagine -> aspartate + ammonia by asparaginase

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17
Q

usefulness of asparaginase?

A

besides breaking down asparagine -> ammonia + aspartate, used to treat some leukemias beacuse asparagine is the AA in lowest level in proteins, so if remove asparagine with asparaginase and hydrolyze it to aspartate, can deplete tumor cell of asparagine and stop it from rapidly growing and dividing

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18
Q

what aa are in the C5 family? what do they make?

A

glutamate, glutamine, histidine, proline, arginine

all metabolized to aKG

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19
Q

how are the c5 family aa broken down?

A

glutamine, histidine, proline, arginine are all converted to glutamate

glutamate is oxidized to aKG by glutamate DH reaction

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20
Q

how does glutamine get metabolized

A

glutamine is hydrolyzed to glutamate + NH3 by glutaminase

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21
Q

how is histidine metabolized

A

histidine’s metabolized to N-formimino glutamic acid

formimino group is transferred to THF to produce N-formimino THF + glutamate

N-Formiminot THF is major source of C for foic acid pool

22
Q

how is arginine metabolized

A

arginine is hydrolyzed to ornithine + urea by arinase

ornithine can produce glutamic semi-aldehyde, which -> glutamate

23
Q

what aa make succinyl CoA?

A

Met, Val, Thr, Isol which -> propionyl CoA -> methylmalonyl CoA -> succinyl CoA

24
Q

what happens to the succinyl CoA made from the succinyl CoA family of aa?

A

breaks down to propionyl CoA

propionyl CoA -> D methylmalonyl -> L methylmalonyl -> succinyl CoA via methylmalonyl CoA mutase rxn

25
Q

what causes methylmalonyl aciduria?

A

inborn error of metabolism causing deficiency of the methylmalonyl CoA mutase or of B12 or of the deoxyadenosyl transferase

26
Q

what are the branched chain aa?

what happens to them in their breakdown?

A

valine, isoleucine, leucine

  1. transamination, which converts the aa to the respective alpha keto acid of that particular amino acid
  2. alpha keto acid undergoes oxidative decarboxylation to produce CO2 and acyl CoA product

this is catalyzed by acyl CoA DH complex

DH complex uses CoA, NAD, FAD, lipoic acid

  1. acyl COA is further metabolized

acyl CoA from valine or isoleucine -> propionyl CoA -> methylmalonyl COA

acyl CoA from leucine -> acetyl CoA & acetoacetate

27
Q

what’s acetoacetate’s categorization?

A

ketogenic because becomes acetoacetate and acetyl CoA, ultimately

28
Q

what causes maple syrup urine disease?

what happens as result?

A

deficiency of branch chain a-keto acid DH needed for breakdown of Val, Iso, Leu

causes accumulation of these aa (Valine, Isoleucine, Leucine), and of the alpha keto acids produced by the transamination reaction

these are toxic compounds to the developing nervous system and cause severe neuro disturbances, failure to thrive, coma, death w/in first 2 years of life

29
Q

how to treat maple syrup urine disease?

A

limit branch chain aa in diet, easy b/c these are all essential aa

30
Q

how does maple syrup urine disease get its name?

A

urine spells like maple syrupe when a-keto acids spill over into the urine

31
Q

how is phenylalanine metabolized?

A

phenylalanine -> tyrosine by phenylalanine hydroxylase

this uses oxygen and THB as cofactor

this is a mixed function oxidation

THB is oxidized to DHB

32
Q

function of THB in phenylalanine catabolism?

A

supplies the reducing equivalents to form the OH of tyrosine and water

it becomes oxidized to DHB

33
Q

how is cofactor regenerated for phenylalanine catabolism?

A

THB is regenerated from DHB by NADPH + DHB reductase

34
Q

what is a mixed function oxidation? when does it occur?

A

in phenylalanine -> tyrosine by phenylalanine hydroxylase, which uses oxygen and THB as cofactor, the 2 atoms of O go to different products:

1 atom of O from O2 is incorporated into tyrosine product

1 atom of O from O2 is incorporated into water

35
Q

is Phe an essential aa? is Tyr?

A

Phe is essential

Tyr is non-essential, as it can be made from Phe

36
Q

what causes phenylketonuria?

A

inborn error of metabolism caused by deficiency of phenylalanine hydroxylase, which converts phenylalanine -> tyrosine *and in some rarer cases, deficiency of THB, the cofactor *

phenylalanine thus accumulates, -> side pathways, produces phenylketones: phenylpyruvate, pheynacetate, and phenyllactate

these cause severe neurological disturbances, mental retardation, death by age 20-30 if not treated

37
Q

incidience of phenylketonuria?

A

20-40/100,000

38
Q

how can you treat PKU? what aa would you add to a diet developed to treat PKU?

A

limit phenylalanine intake

supplement tyrosine intake

39
Q

how does tyrosine catabolism proceed?

A

tyrosine itself or tyrosine from phenylalanine -> fumarate and acetoacetate by this pathway:

  1. tyrosine undergoes transamination, produces para-hydroxyphenylpyruvate
  2. p-hydroxyphenylpyruvate -> homogentisic acid by p-hydroxyphenylpyruate hydroxylase, which require sVitamin C (ascorbic Acid)

**this step is an oxidation, hydroxylation, decarboxylation and ring migration! **

  1. homogentisic acid oxidized to fumarylacetoacetate by homogentisic acid oxidase
40
Q

how are tyrosine and phenylalanine both ketogenic and glucogenic?

A

phenylalanine -> tyrosine

and tyrosine -> fumarate, which is TCA cycle = glucogenic, and acetoacetate, which is ketone body = ketogenic

41
Q

what causes alcaptonuria? how does it manfest?

A

deficiency in the enzyme homogentisic acid oxidase which oxidizes homogentisic acid to fumarylacetoacetate

homogentisic acid is excreted into the urine, which becomes black as homogentisic acid gets further oxidized

not severe disease, but assoc w/ severe arthritis

42
Q

treatment for alcaptonuria?

A

decrease phenylalanine and tyrosine intake

43
Q

how does tryptophan metabolism proceed?

A

broken to alanine, acetyl CoA, and ammonia

thus it’s both ketogenic and glucogenic

44
Q

why are phenylalanine or isoleucine considered both glucogenic and ketogenic aa?

A

because they can form both glucogenic and ketone body intermediates.

Phenylalanine -> fumarate which is a TCA cycle intermediate which -> gluconeogenesis, and

isoleucine -> propionyl CoA -> L/D methylmalonyl CoA -> succinyl CoA -> gluconeogenesis,

however phenylalanine also -> acetoacetate, which is a ketone body, and

isoleucine -> acetyl CoA which + acetoacetyal CoA -> HMG CoA -> acetoacetate.

45
Q

why can’t leuceine be used for glugoneogenesis?

A

because it is catabolized to HmG CoA which is a ketone body intermediate that becomes acetoacetate; it’s not broken down to an intermediate i.e. from the TCA cycle that can undergo gluconeogenesis

46
Q

how would carbon atoms from an aa like alanine wind up in a newly synthesized FA like palmitate?

A

Carbon atoms from an aa like alanine could become part of a FA like palmitate because alanine -> pyruvate via GPT transamination reaction, and pyruvate -> acetyl CoA -> malonyl CoA ->->-> FA synthesis pathway -> palmitic acid

47
Q

what are causes for PKU? how is it treated?

A

PKU is caused by a deficiency in phenylalanine hydroxylase, which converts phenylalanine -> tyrosine; this causes phenylalanine to accumulate and undergo side pathway reactions to phenylketones: phenylpyruvate, phenylacetate, and phenyllactate.

Presence of these compounds causes severe neurological disturbances, mental retardation, and death by age 20-30 if not treated.

This is treatable by restriction of phenylalanine in the diet, while supplementing tyrosine since tyrosine is a metabolic product of phenylalanine catabolism

48
Q

what are casues for MSUD, how is it treated?

A

Maple Syrup Urine Disease is caused by deficiency of a branch chain a-keto acid DH needed for the breakdown of Val, Iso, or Leu.

This causes accumulation of Val, Iso, or Leu, and of a-keto acids produced by the transamination reactions they undergo.

These acids are toxic compounds to the developing nervous system and cause severe neurological disturbances, failure to thrive, coma, and death within the first 2 years of life.

This is treatable by limiting brach chain amino acid in the diet.

49
Q

what is a mixed function oxidase?

A

is a reaction that uses O2, and splits the atoms of O to put each in a different product of the reaction.

In aa catabolism, this occurs with phenylalanine -> tyrosine by phenylalanine hydroxylase, in which 1 atom of O is incorporated into the tyrosine product and 1 atom of O is incorporated into water

50
Q

what is alkaptonuria?

A

caused by a deficiency in homogentisic acid oxidase, which oxidizes homogentisic acid to fumarylacetoacetate.

Homogentisic acid’s excreted into the urine, and thus further oxidized, turning urine black

MCG (77 decks)

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