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MSK_MT1_TBL1 (AA Metabolism) Flashcards

1
Q
A

Glycine

NONpolar, aliphatic

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2
Q
A

Alanine

NONpolar, aliphatic

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3
Q
A

Proline

NONpolar, aliphatic

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4
Q
A

Valine

NONpolar, aliphatic

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5
Q
A

Serine

polar, UNcharged

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6
Q
A

Threonine

polar, UNcharged

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7
Q
A

Cysteine

polar, UNcharged

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8
Q
A

Aspargine

polar, UNcharged

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9
Q
A

Glutamine

polar, UNcharged

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10
Q
A

Leucine

NONpolar, aliphatic

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11
Q
A

Isoleucine

NONpolar, aliphatic

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12
Q
A

Methionine

NONpolar, aliphatic

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13
Q
A

Phenylalanine

Aromatic

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14
Q
A

Tyrosine

Aromatic

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15
Q
A

Tryptophan

Aromatic

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16
Q
A

Aspartate

(-) charged

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17
Q
A

Glutamate

(-) charged

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18
Q
A

Lysine

(+) charged

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19
Q
A

Arginine

(+) charged

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20
Q
A

Histidine

(+) charged

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21
Q

Ketogenic Amino Acids (2)

A
  1. Leucine
  2. Lysine
  • eventually becomes → Acetly CoA or Acetoacetate
  • eventually becomes → precursors for Ketone bodies, fatty acids & isoprenoids
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22
Q

Glucogenic Amino Acids (13)

A
  1. Valine
  2. Histidine
  3. Argenine
  4. Aspargine
  5. Glutamine
  6. Methionine
  7. Alanine
  8. Aspartate
  9. Gluatmate
  10. Glycine
  11. Proline
  12. Serine
  13. Cystine
  • eventually becomes → Pyruvate/TCA cycle intermediates (oxaloacetate, α-ketogluterate, succinyl coA, fumerate)
  • eventually becomes → precursors for glucose synthesis via glucogenogenisis
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23
Q

Ketogenic & Glucogenic Amino Acids (5)

A
  1. Isoleucine
  2. Tryptophan
  3. Phenylalanine
  4. Tyrosine
  5. Threonine
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24
Q

Roles of AA (Big Picture)

A
  • aids with the removal of excess ammonium ion (NH₄⁺​) from brain
  • aids with the removal of excess ammonia ( NH3) from skeletal muscles (via glucose-alanine cycle)
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25
Q

Fates of Tryptophan (3)

A
  1. Niacin
  2. Serotonin
  3. Melatonin
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26
Q

Fate of Histidine

A

Histamine

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27
Q

Fate of Glycine

A

Heme

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28
Q

Fates of Arginine (3)

A
  1. Creatine
  2. Urea (CH₄N₂O)
  3. Nitric Oxide (NO)
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29
Q

Fate of Glutamate

A

GABA (neurotransmitter)

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30
Q

Defect in Branched Chain AA leads to…

A

Maple Syrup Urine Disease

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31
Q

Defect in Homocysteine leads to …

A

Homocystinuria

  • body can’t process Methionine = harmful build-up of substances in the blood and urine
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32
Q

Defect in Cysteine leads to …

A

Cystinuria

  • excessive amounts of undissolved cystine in the urine = bladder stones
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33
Q

Transamination

A

chemical rxn between an amino acid ( contains an amine NH2 group) & a keto acid (which contains a keto =O group)

  • NH2 is exchanged with the =O group
  • produces an α-keto acid from the amino acid and glutamate from α-ketoglutarate

catalyzed by aminotransferases (revisible rxn)

34
Q

Aspartate aminotransferase (AST)

A

reversibly transaminates aspartate → oxaloacetate

35
Q

Alanine aminotransferase (ALT)

A

reversibly transaminates alanine → pyruvate.

36
Q

Pyridoxal phosphate (PLP)

A
  • derived from vitamin B6 (pyridoxine)
  • required cofactor for all aminotransferases.
37
Q

5 Amino Acid Families

A
  1. Serine Family
  2. Pyruvate Family
  3. Aspartate Family
  4. Glutamate Family
  5. Aromatic Family
38
Q

Serine Synthesis Pathway

A
  • synthesized from 3-phosphoglycerate (glycolytic intermediate)
    • three rxns:
      1. add ammonia
      2. add -OH group
      3. remove phosphate
  • required for synthesis of phosphatidylserine, cysteine, glutathione

Big Picture:

3-phosphoglycerate → → 3-Phosphoserine → Serine

39
Q

Pyruvate Synthesis Pathway

A
  • Pyruvate also makes Alanine and Leucine
  • Glucose-alanine cycle:
  • Alanine plays a special role in transporting amino groups → liver.
    • It is the carrier of ammonia & carbon skeleton of pyruvate from muscle → liver.
      • The ammonia is excreted
      • pyruvate recycled → glucose, which is returned to the muscle.
40
Q

Aspartate Synthesis Pathway: Apartate

A
  • synthesized from oxaloacetate
    • catalyzed by aspartate aminotransferase (AST)
    • NH3 transferred from glutamate
    • requires pyridoxal phosphate (PLP) cofactor
  • neurotransmitter; also required for synthesis of purines, pyrimidines, inositol, & urea
  • moves between cytosol ⇌ mitochondria
    • via aspartate-malate shuttle
41
Q

Aspartate Synthesis Pathway: Asparagine

A
  • synthesized from aspartate
    • catalyzed by asparagine synthetase
  • glutamine used as source of nitrogen
  • leukemic cells low in this enzyme
    • epigenetic silencing by methylation
42
Q

Aspartate Family: Other Important Derivatives from Asp

A
  1. Lysine
  2. Threonine
  3. Methionine (Homo-cysteine)
43
Q

Glutamate Synthesis Pathway: Glutamate

A
  • synthesized from α-ketoglutarate
    • catalyzed by glutamate dehydrogenase​
  • neurotransmitter (GABA)
44
Q

Glutamate Synthesis Pathway: Glutamine

A
  • synthesized from *glutamate*
    • catalyzed by glutamine synthetase
  • conditionally essential in neonates & under stress conditions
45
Q

Glutamate Synthesis Pathway: Proline & Argenine

A
  • synthesized from *glutamate*
    • catalyzed by glutamine synthetase
46
Q

Cystine Family Synthesis Pathway

A
  • synthesized from *SERINE*
    • reaction part of methionine catabolic pathway
    • sulfur derived from methionine
  • cysteine becomes conditionally essential in individuals whose diet is limiting in methionine
  • required for synthesis of glutathione

Big Picture

Serine + Homocysteine → Cystathionine → Cysteine​

47
Q

AAs that form Succynil CoA

A
  1. methionine
  2. cysteine

pathway produces acetylcholine

48
Q

Importance of B12 (Folate) and B6 (Pyroxidine) in Methionine Catabolism

A

Two Disposal Pathways for Homocysteine:

  1. Conversion to Methionine
    • requires folate (B12)
    • is a RE-methylation rxn
      1. Formation of Cysteine
        1. requires pyridoxine (B6)
        2. is a transSULFERATION rxn
      2. sulfur of methionine → sulfur of cysteine
49
Q

AA Degradation

A

Important AA catabolites include:

  1. ammonia
  2. CO2
  3. long-chain and short-chain fatty acids
  4. glucose
  5. ketone bodies
  6. nitric oxide (NO)
  7. urea
  8. uric acid
  9. polyamines
  • complete oxidation of AA ultimately requires conversion to acetyl-CoA,
    • which is _oxidized to CO2 and H2O (_via the TCA cycle ETC)
  • less efficient for ATP production compared with fat & glucose
50
Q

α-ketoglutarate Degradation

A
  1. arginine & proline → glutamate γ- semialdehyde → glutamate → α-ketoglutarate
    • first step in arginine degradation catalyzed by arginase (urea cycle enzyme)
  2. histidine → glutamate → α-ketoglutarate
  3. glutamine → glutamate → α-ketoglutarate
  • GLUTAMATE*:
  • converted to α-ketoglutarate via transaminase or glutamate dehydrogenase
51
Q

Methionine Degradation

A

methionine metabolism (after a meal):

  1. excess methionine → homocysteine
  2. homocysteine → cystathionine & α-ketobutyrate

• catalyzed by cystathionine synthase and lyase both require PLP (vit. B6)

52
Q

Propionyl CoA Covertion → Succinyl CoA

A

rxn also needed for odd-chain fatty acid degradation

  • catalyzed by methylmalonyl CoA mutase
  • requires vitamin B12 (Folate)
53
Q

Methylmalonic acidemia

A
  • inherited enzyme (Methylmalonyl CoA mutase) deficiency OR inability to convert vitamin B12 → coenzyme form

TREATMENT

  • low protein diet supplemented with vitamin B12
54
Q

Branched Chain AA Degradation

A

Valine & Isoleucine → Succinyl** CoA (gluconeogenesis**)

Leucine → Acetyl CoA (ketogenesis)

Common Enzymes:

  1. first step via branched-chain aminotransferase
  2. second step via branched-chain α-keto acid dehydrogenase complex
    • ​​if this enzyme is defective = Maple Syrup Urine Disease
55
Q

Maple Syrup Urine Disease

A
  • = branched-chain α-keto acid dehydrogenase (BCAD) deficiency
    • autosomal recessive
    • BCα-K excretion into urine = “maple syrup” odor

​Symptoms

  • poor feeding/ vomiting
  • lethargy
  • developmental delay
  • If untreated → seizures, coma, death

Treatment

  • protein restricted diets supplemented with thiamin (vitamin B1)
    • adding Thiamine (B1) ensures maximal activity from residual BCAD complex
56
Q

4 AA Degraded to Pyruvate

A
  1. tryptophan → alanine (also acetyl CoA for ketogenesis)
  2. alanine → pyruvate (by alanine aminotransferase)
  3. cysteine → pyruvate (through loss of the sulfur)
  4. serine → pyruvate (via serine dehydratase; requires PLP [vit. B6])

Pyruvate converted to:

  • oxaloacetate for gluconeogenesis (liver): fasting, starvation, and uncontrolled diabetes
  • acetyl CoA for TCA* cycle or *fatty acids: post-prandial (all tissues)
57
Q

Cystathionuria

A

(Methionine and Threonine Catabolism)

  • rare deficiency in cystothionase = accumulation in cystathionine
  • benign condition
58
Q

Homocystinuria

A

(Methionine and Threonine Catabolism)

due to deficiency in cystathionine synthase

  • ↑↑ of homocysteine in urine
  • methionine & homocysteine ↑↑ in blood
  • CYSTEINE ↓↓

leads to:

  • skeletal abnormailities
  • ↑↑ risk of clotting
  • lens dislocation
  • intelectual diability
59
Q

Aromatic Family

(Big Picture)

A
  1. Histadine
  2. Phenylalanine
  3. Tyrosine
  4. Tryptophan

Needed for

  • Dopamine, Norepinephrine, Epinephrine
  • Thyroid hormones, Melanin

Disorders:

  1. Phenylketonuria (PKU)
  2. Albinism
60
Q

Histadine

A

Ribose 5-phosphate →→ Histidine →→ alpha ketoglutarate.

Removal of carboxylic acid group by decarboxylase from Histidine = Histamine (requires Vitamin B6 pyridoxine):

  • (Histidine + decarboxylation = histamine)
  • involved in the inflammatory response.
  • regulate HCl secretion by gastric mucosa
61
Q

Histidinemia

A

due to defect in histidase, harmful and untreatable.

Histidinemia Symptoms:

  • ↑↑↑ of histidine
  • mentally retarded with defect in speech
62
Q

Tyrosine Big Picture

63
Q

Phenylalanine → Tyrosine

A

tyrosine synthesized from phenylalanine (an essential AA)

  • by phenylalanine hydroxylase
    • requires 5,6,7,8-tetrahydrobiopterin cofactor (small amounts)
      • dihydrobiopterin reductase recycles product 7,8-dihydrobiopterin
  • rate-limiting step in catecholamine (neurotransmitters) synthesis

NOTE: tyrosine is the only non-essential AA synthesized from an essential AA

64
Q

Phenylketonuria (PKU)

A

Classic PKU: phenylalanine hydroxylase deficiency

  • autosomal recessive
  • ↑↑↑ phenylalanine levels (>1200 µM) = severe brain damage
    • results in cognitive disabilities with seizures (if untreated)

Treatment

  • LOW phenylalanine diets (& supplemental amino acids)
  • treated patients mature normally

NOTE: pregnant PKU women that were not on low phenylalanine diet before conception produce abnormal child (maternal PKU; a teratogenic disorder)

65
Q

Tetrahydrobiopterin Responsive PKU

A

dihydrobiopterin reductase deficiency

  • autosomal recessive [1/106 births]
  • more severe (more profound cognitive disabilities, hypertonia, seizures)
    • WHY? - other pathways also require tetrahydrobiopterin
    • e.g., norepinephrine & epinephrine from tyrosine; nitric oxide from arginine
66
Q

Toxic Phenylalanine Metabolism

A

alternate metabolism of EXCESS phenylalanine (aminotransferase: pyruvate → alanine)

  • results in excessive amounts of phenylacetate & phenyllactate; toxic for the brain!!
  • ↑↑↑of phenylpyruvate = “musty” or “mousy” odor in urine
  • [↑↑↑] phenylalanine in blood REDUCES brain uptake of other AA

Treatment: sapropterin dihydrochloride (Kuvan)

  • derivative of tetrahydrobiopterin
  • given large doses to ensure maximal activity of residual phenylalanine hydroxylase
  • most likely to be effective in classic PKU patients with mild hyperphenylalaninemia
67
Q

5 AA Degraded to Acetyl CoA

A
  1. Tryptophan
  2. Phenylalanine
  3. Tyrosine
  4. Leucine
  5. Isoleucine

hydrophobic AA degraded to acetoacetyl CoA & acetyl CoA (ketogenesis)

  • pathways similar to fatty acid degradation
  • can also Fumarate & Succinyl CoA & pyruvate
68
Q

Inherited Disorders of Tyrosine Degradation: Tyrosinemia II

A

inherited deficiency of tyrosine aminotransferase

  • autosomal recessive
  • 1st step of tyrosine degradation pathway inhibited

Symptoms:

  • erosions of cornea, palm, soles
    • due to tyrosine crystals in cells & extracellular matrix

Treatment: low tyrosine diet

69
Q

Inherited Disorders of Tyrosine Degradation: Tyrosinemia III

A

inherited deficiency p-hydroxyphenylpyruvate dioxygenase

  • 2nd step in pathway inhibited
    • produces homogentisate

BENIGN: because p-hydroxyphenylpyruvate readily excreted in urine

70
Q

Inherited Disorders of Tyrosine Degradation: Alkaptonuria

A

inherited deficiency of homogentisate 1,2-dioxygenase

3rd step (opens phenol ring) in pathway inhibited

autosomal recessive

homogentisate excreted in urine: forms dark pigment under basic conditions in presence of oxygen

accumulates in soft tissues and joints (induces arthritis & disc calcification)

71
Q

Inherited Disorders of Tyrosine Degradation: Tyrosinemia I

A

inherited deficiency of fumarylacetoacetase

  • 4th step via maleylacetoacetate isomerase
    • produces fumarylacetoacetate via isomerization
  • 5th step via fumarylacetoacetase
    • hydrolysis rxn produces fumarate & acetoacetate → acetoacetyl-CoA
  • autosomal recessive (1/10^5 births worldwide)​

MOST SEVERE TYROSINEMIA

  • presents in early infancy with failure to thrive, vomiting, jaundice, hepatomegaly, elevated liver enzymes & bleeding tendency
  • requires liver transplant for cure
72
Q

Tryptophan Synthesis and Derivatives

A

General scheme of the Tryptophan synthase reaction:

  • Indole-3-Glycerole-P → Indole → Tryptophan

Tryptophan Catabolism:

  • Tryptophan → Acetyl CoA → Energy or Ketone Bodies (glucogenic and ketogenic)
73
Q

Clinical Correlations: Phenyl Alanine

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme:Phenylalanine hydroxylase

Accumulated Product: Phenylalanine

Disease: PKU (Classical)

Symptoms: Musty or mousy odor in urine, mental retardation and accumulation of phenyl pyruvic acid, phenylacetate and phenyllactate in urine.

74
Q

Clinical Correlations: Phenyl Alanine (Non-Classic)

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme: Dihydropterindine reductase

Accumulated Product: Phenylalanine

Disease: PKU (non-classical)

Symptoms: Mental retardation and PKU classic symptoms

75
Q

Clinical Correlations: Tryrosine

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme: Homogentisate oxidase

Accumulated Product: Homogentisate

Disease: Alkaptonuria

Symptoms: Black urine, arthritis

76
Q

Clinical Correlations: Tryrosine I

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme: Fumarylacetoacetate hydrolase

Accumulated Product: Fumarylacetoacetate

Disease: Tyrosinemia I

Symptoms: Liver failure, early death, failure to thrive, vomiting and elevated liver enzymes, cabbage-like odor

77
Q

Clinical Correlations: Tryrosine II

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme: Tyrosine aminotransferase

Accumulated Product: Tyrosine

Disease: Tyrosinemia II

Symptoms: Neurologic defects

78
Q

Clinical Correlations: Tryrosine III

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme: para-Hydroxy phenylpyruvate dioxygenase

Accumulated Product: Para-Hydroxy phenylpyruvate (but excreted via urine)

Disease: Tyrosinemia III

Symptoms: BENIGN

79
Q

Clinical Correlations: Branched Chain AA (LEU, ISO,VAL)

Defective Enzyme:?

Accumulated Product:?

Disease: ?

Symptoms: ?

A

Defective Enzyme: Branched-chain-α-keto acid dehydrogenase

Accumulated Product: α-keto acids of Leucine, Isoleucine and Valine

Disease: Maple Syrup Urine Disease (MSUD)

Symptoms: Urine smells like maple syrup or burnt sugar. Mental retardation, poor feeding, vomiting, lethargy, developmental delay. If untreated leads to coma and death

80
Q

Summary Charts

MSK_Y1_MT1 (13 decks)

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