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Biochemistry MBBS > Amino Acids > Flashcards

Amino Acids Flashcards

1
Q

Both ketogenic and glucogenic amino acid

A
  1. Phenylalanine and tyrosine (tyrosine transaminase)
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2
Q

Tyrosine products

A
  1. Melanin (tyrosinase)
  2. Catecholamines (tyrosine hydrolase)
  3. Thyroxine (iodination)
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3
Q

Explain hydroxylation of phenyl alanine

A

Phenyl alanine hydroxylase

Tetra hydrobiopterin to dihydrobiopterin which is recycled by NADPH dependent dihydrobiopterin reductase

(tetrahydrobiopterin is formed from GTP by GTP Cyclo hydroxylase)

Irreversible reaction

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4
Q

Defects in phenylalanine hydroxylase reaction

A
  1. Defect in the enzyme is Phenyl ketonuria Type I (Classic)
  2. In dihydrobiopterin reductase , causes PKU type 2 and 3 (non classic)
  3. BH4 formation defect, PKU type 4 and 5 (non classic)
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5
Q

Vitamin c requiring enzyme in tyrosine metabolism

A

PHPP hydroxylase
(dioxygenase)

Type 3 tyrosinemia

which converts PHPP ( pyruvate equivalent of tyrosine ) to homogentisate

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6
Q

Step in tyrosine metabolism requiring Fe2+

A

Homogentisate oxidase (dioxygenase)

Alkeptonuria

Converting homogentisate to maleyl acetoacetate (MAA)

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7
Q

GSH requiring enzyme in tyrosine metabolism

A

MAA cis trans isomerase

Which converts maleyl acetoacetate (MAA) to Fumaryl acetoacetate

(Which is later split by fumaryl acetoacetate hydrolase
Type 1 tyrosinemia)

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8
Q

Substances that activate the steps of tyrosine metabolism

A
  1. Vitamin C activates PHPP hydroxylase (Type 3 tyrosinemia)
  2. Fe+2 activates Homogentisate oxidase (Alkeptonuria)
  3. GSH activates MAA cis trans isomerase

Later fumaryl acetoacetate hydrolase acts
(Type 1 tyrosinemia)

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9
Q

Tyrosinemia type 1

A

Hereditary Tyrosinemia/hepatorenal tyrosinemia
Most common

FAA hydrolase

Resembles porphyria
Cabbage like odour

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10
Q

Treatment for hepatorenal tyrosinemia and alkeptonuria

A

Nitisinone NTBC

Inhibits PHPP hydroxylase

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11
Q

Type 2 tyrosinemia

A

Oculocutaneous / Richner Hanhart syndrome

Tyrosine transaminase
Corneal ulcer
Nonpruritic hyperkeratotic plaque seen in soles and palms

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12
Q

Type 3 tyrosinemia

A

Neonatal tyrosinemia

Least common

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13
Q

Hawkinsonuria

A

Mutant enzyme is PHPP hydroxylase (enzyme of type 3 tyrosinemia)

Swimming pool odour
Compound hawkinson produced

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14
Q

PKU

A

Phenyl alanine hydroxylase
Phenylacetate is responsible for mousy or musty odour
Hypopigmentation not albinism (blue eyes, blonde hair,fair skin)

Neurological manifestations(due to decreased thyroxine and neurotransmitter due to…)

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15
Q

Infants and PKU

A

Severe vomiting often misdiagnosed as congenital hypertrophic pyloric stenosis

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16
Q

Diagnosis of PKU

A
  1. Guthrie bacterial inhibition test using Bacillus subtilis
  2. Ferric chloride test (transient blue green colour) by phenyl pyruvate
  3. Blood phenylalanine level >20 mg/dl
  4. Tandem mass spectrometry /Fluorometric analysis
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17
Q

Treatment of PKU

A
  1. Restrict phenylalanine
  2. Sapropterin dihydrochloride /Kuvan (synthetic tetrahydrobiopterin)
  3. Large neutral amino acid (to prevent toxicity by phenylalanine saturation to tyrosine and tryptophan transport )
  4. Recombinant therapy using phenylalanine ammonia lyase
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18
Q

Alkeptonuria ( part of Garrods tetrad (CAAP))

First inborn error to be detected

A

Benzoquinone acetate (reducing agent) is polymerised to alkeptonuria bodies in pinna ,sclera,…(blackish spots)

Ochronosis due to accumulation in cartilage

Low back ache in middle age

Blackish discloration in the top layers
Black or red in diaper

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19
Q

Lab diagnosis of alkeptonuria

A
  1. Alkalanisation of urine
  2. Ferric chloride test
  3. AgNO3 test
  4. X-ray of spine-
    parrot beak appearance
    Bamboo like spine
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20
Q

Segawa syndrome

A

GTP cyclohydrolase

Autosomal dominant ,in females

Dystonia with diurnal variation
BH4 level reduced
Phenylalanine level normal

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21
Q

Synthesis of DOPA

A
  1. Tyrosine hydroxylase (RDS)
  2. DOPA decarboxylase( with PLP)
  3. Dopamine beta oxidase
  4. N Methyl transferase (with SAM)
22
Q

The 3 aromatic amino acid hydroxylases requiring tetrahydrobiopterin, NADPH

A
  1. Phenylalanine hydroxylase
  2. Tyrosine hydroxylase
  3. Tryptophan hydroxylase

These are monooxygenases

23
Q

Degradation of catecholamines

A
  1. Dopamine- Homo Vanillic Acid
  2. Epinephrine - (COMT) metanephrine - (MAO) Vanillyl Mandelic acid
  3. Norepinephrine -(COMT) normetanephrine - (MAO) VMA

COMT - CatecholOMethyl transferase
MAO - Monoamine oxidase

24
Q

Triad of pheochromocytoma

A

Palpitation, headache, Profuse sweating

25
Melanin
Tyrosine to DOPA then to Dopaquinone by tyrosinase | Then to melanin
26
Albinism
Milky white skin and hair | Red eye reflex
27
Sulphur test is answered by
Cysteine ,not methionine | Both are glucogenic
28
Formation of SAM
Methionine adenosyl transferase (MAT) This enzyme has 3 isoforms MAT 1 and 3 are present in hepatic tissues MAT 2 is present in the extra hepatic tissues
29
Significance’s of SAM
1. Transmethylation reactions a) creatine b) epinephrine c) metanephrine d) choline e) anserine f) melatonin 2. Polyamines 3. DNA methylation
30
Polyamines formation
1. Cadaverine (lysine on decarboxylation 2. Putrescin (ornithine on decarboxylation via ornithine decarboxylase RDS) 3. Spermidine (putrescin accepts amino group from decarboxylated SAM) 4. Spermine ( spermidine accepts amino in the same way)
31
Polyamine function
Positively charged so interact with DNA and regulate gene expression Excreted in some cancers
32
Formation of Homocysteine
From SAH (formed via methyl transferase) which is acted by adenosyl homocysteinase to get homocysteine
33
Formation of methionine from homocysteine
N5 Methyl THFA is coupled with methyl B12 If there is vitamin deficiency of B12 , folic acid or PLP, it leads to homocystinuria, not homocysteinuria. Thus CVA, CAD increases.
34
Transulfuration reactions
Homocysteine + serine = cystathionine (via cystathionine beta synthase and PLP) = homoserine + cysteine (via cystathionase and PLP)
35
Fate of homoserine
Converted to propionyl CoA then to succinyl CoA then via TCA to glucogenic
36
Oast House syndrome | / Smith Strang disease
Defect in methionine transporter which transports methionine from intestine to blood
37
Primary hyper methioninemia
Deficiency of MAT | Smell of boiled cabbage
38
Classic homocystinuria (no E)
Deficiency of cystathionine beta synthase
39
Cystathioninuria
Defect of cystathionase | Cyanide nitroprusside test -ve
40
Non classic homocystinuria (no E) | Causes
Deficiency in N5 THFA (from folic acid) or methyl B12 1. N5 THFA deficiency may occur due to defect in MTHFR (Methylene THF reductase) Megaloblastic anaemia absent 2. B12 deficiency Megaloblastic anaemia present
41
Classic homocystinuria | Clinical features
1. Developmental delay 2. Around 3 years, decreased vision, progressive myopia and quivering of eye (iridodonesis) Medial and downward dislocation of lens (ectopia lentis) 3. Skeletal deformities 4. Severe mental retardation 5. Thromboembolism Resembles Marfans syndrome
42
Skeletal deformities of classic homocystinuria
1. Pectus cavinatum or pectus excavatum 2. Arachnodactyly 3. Knee deformities Genu valgum/ varum 4. Coxa vara Pescavus 5. High arched palate
43
Diagnosis and screening of homocystinuria
Diagnosis by Cyanide nitroprusside test (magenta colour) ,answered by homocysteine, homocystine, cysteine and cystine. Screened by tandem mass spectrometry
44
Treatment of classic homocystinuria
1. High doses of vitamin B6
45
Non classic homocystinuria
Homocysteinemia | Methionine level is decreased but cysteine level is normal
46
Cystinuria
Part of Garrods tetrad (CAAP) Defect in diabetic amino acid transporter in intestine and renal tubules COLA in urine Cystine (no E) ,ornithine, lysine, arginine Cyanide nitroprusside test +ve
47
Cystinosis
Lysosomal storage disorder H+ driven cystine transporter called cystinosin (of gene CTNS) Hepatic failure, renal failure, corneal opacity, bone marrow also affected
48
Treatment of cystinosis
Cysteamine which converts cystine to cysteine
49
Cysteine functions
1. On decarboxylation gives betamercapto ethanolamine 2. CoA 3. Taurine (bile acids) 4. Glutathione 5. Cystine
50
Glutathione
Tripeptide (gamma glutamyl cysteinyl glycine) | Pseudopeptide (not an alpha carboxyl bond)
51
Functions of glutathione
1. Meister cycle (for amino acid transport) 2. RBC membrane integrity 3. Maintains Fe as +2 4. Phase 2 xenobiotic reactions- conjugating agent 5. Antioxidant 6. Coenzyme of cis trans isomerase MAA to FAA
52
Enzymes involved in RBC membrane integrity
Glutathione peroxidase containing selenocysteine (which converts H2O2 to H2O by formation of GSSG) GSSG is recycled back to GSH by glutathione reductase (containing riboflavin) and NADPH

Biochemistry MBBS (10 decks)

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