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Biochemistry > Fate of Carbon Skeleton in Amino Acid pt.2 > Flashcards

Fate of Carbon Skeleton in Amino Acid pt.2 Flashcards

1
Q

How is phenylalanine catabolised?

A

It is hydroxylated to tyrosine by the enzyme phenylalanine hydroxylase

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2
Q

What is the co-factor for phenylalanine hydroxylase?

A

tetrahydrobiopterin

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3
Q

What 3 situations may lead to Phenylketonuria?

A

deficiency of phenylalanine hydroxylase
deficiency of tetrahydrobiopterin
deficiency in the reductase that regenerates the co-factor (dihydropteridine reductase)

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4
Q

What characterizes phenylketonuria?

A

it is characterized by the accumulation of phenyl ketones in the blood and their excretion in the urine

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5
Q

How are the compound derivatives of phenylalanine formed and what are they?

A

by transamination

they are phenylpyruvic acid, phenylacetate and phenyllactate (reduced forms of former)

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6
Q

What imparts the mousy odor of urine in phenylketonuriacs?

A

phenylacetate

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7
Q

When does the musty odor of urine occur in phenylketonuriacs?

A

2-6 weeks after elevated blood phenylalanine

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8
Q

Apart from musty odor of breath or urine, what other symptoms do phenylketonuriacs present with?

A

severe mental retardation
low IQ
dilution of hair and skin pigmentation

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9
Q

In terms of genetics, what type of disease is PKU?

A

autosomal recessive disease

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10
Q

How can PKU be managed?

A

restriction of phenylalanine containing diets
taking diets high in tyrosine for first 4-5 years
protein diet restriction should be enforced for years
diets should contain high levels of tetrahydrobiopterin

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11
Q

If the symptoms of PKU are caused by excess Phe and its metabolites and since Phe is essential, what can be done?

A

treatment will involve careful monitoring of Phe intake just enough for protein synthesis without accumulating Phe

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12
Q

Phenylketonuriacs should avoid processed food and beverages containing a food additive ……………

A

aspartame

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13
Q

The 4 metabolic fates of tyrosine

A
  • catabolism to acetoacetyl CoA
  • synthesis of catecholamines
  • synthesis of melanin
  • synthesis of thyroid hormones
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14
Q

How is tyrosine converted to dihydroxyphenylalanine (L-DOPA)?

A

it is oxidized by tyrosine hydroxylase with enzyme co-factor tetrahydrobiopterin

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15
Q

Dihydroxyphenylalanine(L-DOPA) is a metabolic precursor to ………

A

dopamine

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16
Q

Tyrosine is a precursor to pigment molecules called ………. that are produced from ………….

A

melanin

dopaquinone

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17
Q

The 2 primary melanins and their colours?

A

eumelanin - black

pheomelanin - yellow/red

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18
Q

What makes pheomelanin have its colour?

A

the sulfur in the cysteine that is combined with dopaquinone

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19
Q

3 main rxns in tyrosine catabolism

A

transamination
dioxygenation
isomerization rxns

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20
Q

What is Tyrosinemia?

A

a condition characterized by the accumulation and excretion of tyrosine and its metabolites

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21
Q

What condition my cause temporarily high tyrosine levels in 10% of neonates?

A

Vitamin C deficiency or immature liver enzymes due to prematurity

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22
Q

The occurrence of tyrosinemia in males and females

A

happens in males and females equally

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23
Q

What is Type 1 Tyrosinemia characterized by?

A

deficiency of fumaryl acetoacetase

24
Q

Type 1 Tyrosinemia is associated with

A

the accumulation of maleyl acetoacetate and fumaryl acetoacetate

25
Q

When can the 2 forms of Type 1 Tyrosinemia and when do they manifest?

A

acute form - a few months after birth

chronic form - around 1 year after birth

26
Q

Symptoms of the acute Type 1 Tyrosinemia

A

poor appetite and failure to grow normally
vomiting, diarrhoea and bloody stool
cabbage-like odour, jaundice, hepatitis
irritability and lethargy

27
Q

Symptoms of chronic Type 1 Tyrosinemia

A

liver cirrhosis
polyneuropathy and kidney problems
episodes of intense abdominal pains
heart muscle weakness

28
Q

Chronic Type 1 Tyrosinemia is otherwise referred to as

A

Hepato-renal Tyrosinemia

29
Q

What is Type 2 Tyrosinemia characterized by?

A

deficiency of tyrosine aminotransferase

30
Q

What is Type 2 Tyrosinemia associated with?

A

eye and skin lesions

mental retardation

31
Q

When do symptoms of Type 2 Tyrosinemia start and what are some of them?

A 
begin in early childhood
excessive tearing
abnormal sensitivity to light
eye pain and redness
painful skin lesions on palm and soles
intellectual disability in about 50%
32
Q

Type 2 Tyrosinemia is otherwise called

A

Oculo-cutaneous Tyrosinemia or Richner-Hanhart Syndrome

33
Q

Type 3 Tyrosinemia is characterized by

A

deficiency of 4-hydroxy phenylpyruvate dioxygenase (4HPD)

34
Q

Type 3 Tyrosinemia is associated with

A

Intellectual disability
Seizures
Periodic loss of balance or coordination(intermittent attaxia)

35
Q

What is Homogentisic Aciduria characterized by?

A

the deficiency of Homogentisate 1,2 dioxygenase

36
Q

Homogentisic Aciduria is associated with

A

accumulation and excretion of large amounts of homogentisic acid

37
Q

What leads to darkening of napkins of individuals with Homogentisic Aciduria?

A

exposure of homogentisic acid to air polymerizes it to alkapton

38
Q

Symptoms of Homogentisic Aciduria

A

Alkapton deposits in bones, connective tissue and other organs leading to ochronosis

39
Q

Albinism is characterized by

A

deficiency of tyrosinase

40
Q

Associations of Albinism

A

Defective synthesis of melanin in hair, skin and eyes
Extreme sensitivity to light
Poor eyesight
Highly susceptible to sunburn and skin cancer

41
Q

The genetic association with albinism is

A

it is an autosomal recessive genetic mutation in the tyrosinase gene

42
Q

Histidinaemia is characterized by

A

deficiency in histidine ammonia lyase

43
Q

Histidinaemia is associated with

A

high levels of histidine in blood and urine

44
Q

Symptoms of Histidineamia

A

speech defects

mental retardation

45
Q

Deficiency and vitamin B12(folic acid) will result in

A

excretion of excessive amounts of formiminoglutamate(FIGLU)

46
Q

How is Hydantoin 5 propionate excreted?

A

through the urine

47
Q

Catecholamines are amino derivatives of catechol and they are

A

DOPA(Dihydroxyphenyl alanine)
dopamine
epinephrine
norepinephrine

48
Q

4 reactions of that form catecholamines and their enzymes

A

Tyrosine —-> L-DOPA (tyrosine hydroxylase)
L-DOPA —–> Dopamine + carbon dioxide (aromatic acid decarboxylase)
Dopamine —> Norepinephrine (Dopamine β-hydroxylase)
Norepinephrine —> Epinephrine (requires S-adenosyl methionine)

49
Q

What are the 2 steps that convert tryptophan to serotonin

A

Tryptophan —> 5-hydroxytryptophan by trp hydroxylase, requires tetrahydrobiopterin
5-hydroxytryptophan —> serotonin + carbon dioxide by aromatic acid decarboxylase

50
Q

Parts of the body where serotonin is formed

A

brain(neurotransmitter; regulation of mood, sleep and attitude)
platelets(platelet aggregation, vasoconstriction)
smooth muscles(contraction)
GIT (enterochromaffin cells; major storage site)

51
Q

Serotonin will go through 2 steps to form

A

melatonin

52
Q

Uses of melatonin

A

induces skin lightening
supresses ovarian function
possible use in sleep disorders

53
Q

Which amino acid is the precursor of nicotinic acid

A

tryptophan

54
Q

What is the precursor of serine

A

glucose

54
Q

What is the precursor of serine

A

glucose

55
Q

What amino acid is involved in the production of glycine?

A

serine

Biochemistry (9 decks)

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