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MEH > Proteins And Amino Acid Metabolism + PKU + Homocystinuria > Flashcards

Proteins And Amino Acid Metabolism + PKU + Homocystinuria Flashcards

1
Q

Outline phenylketonuria

A

Deficiency in phenylalanine hydroxylase

  • Causes an accumulation of phenylalanine as it cant be converted to tyrosine
  • Phenylalanine becomes transaminated to phenylpyruatve
  • Accumulation of phenylketones
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2
Q

Symptoms of PKU

A

Phenylketones in urine > musty smell
Severe intellectual disability
Developmental delay
Small head
Seizures
Hypopigmentation

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3
Q

Outline homocystinuria

A

Cannot breakdown methionine to cysteine
Defect in cystathionine B-synthase
Build up of homocysteine > excreted in urine

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4
Q

Treatment of homocystinuria

A

Low methionine diet
Less milk, meat, fish, cheese, eggs + nuts
Cysteine, vitamin B6, 12 and folate supplement

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5
Q

Supplements can be used to treat homocystinuria
What supplement and why?

A

Vitamin V6, B12 + folate

Homocysteine > methionine is promoted by them
Less accumulation of homocysteine

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6
Q

Treatment of PKU

A

Low phenylalanine diet
High tyrosine diet
Avoid artifical sweeteners
Avoid high protein foods - meat, milk + eggs

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7
Q

Homocystinuria and Marfan’s;s syndrome have some similar clinal feature
What are they?
How can you distinguish between the two?

A

Similar:
- skeletal deformities
- lens dislocation

Different
- homocystine levels high in homocystinurea but normal in Marfan’s

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8
Q

What is creatinine?

A

Breakdown product of creatine and creatine phosphate in muscles

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9
Q

What does creatinine a useful clinical marker of?

A
  • Real function
  • Estimates muscle mass - Creatinine urine excretion over 24h is proportional to muscle mass
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10
Q

What is an abnormal nitrogen balance?

A

negative N balance - Intake < output

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11
Q

Causes of a negative nitrogen balance

A

Trauma
Infection
Malnutrition

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12
Q

What are three major nitrogen containing compounds?

A

Amino acid
Proteins
Purine + pyrimidine

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13
Q

What is nitrogen balance?

A

Nitrogen input - nitrogen output

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14
Q

When is a positive nitrogen balance normal?

A

Growth
Pregnancy
Adult recovering from malnutrition

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15
Q

What is protein turnover?

A

Balance between protein synthesis and protein degradation

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16
Q

Example of a glucogenic amino acid

A

Alanine

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17
Q

Example of a ketogenic amino acid

A

Leucine

18
Q

Example of both a glucogenic and ketogenic amino acid

A

Isoleucine

19
Q

When does mobilisation of protein reserves occur?

A

Extreme stress - starvation

20
Q

What are the 9 essential amino acids?

A

Isoleucine
Lysine
Threonine
Histidine
Leucine
Methionine
Phenylalanine
Tryptophan
Valine

If Learned This Huge List May Prove ** Truly Valuable

21
Q

What amino acids can be conditionally essential and when?

A
  • Tyrosine - low in phenylalanine or phenylalanine hydroxylase deficient
    -Cysteine - low in methionine
  • Arginine

Or in pregnancy and children

22
Q

Where do carbon atoms for non-essential amino acid syntehsis come from?

A

Glycolysis intermediates
Pentose phosphate pathway
Kerbs cycle

23
Q

What are the pathways which facilitate removal of nitrogen from amino acids?

A

Transamination
Deamination

24
Q

Outline transamination

A
  • Transfers amine group from one amino acid to another group e.g. keto acid
  • require the coenzyme pyridoxal phosphate
25
Q

What are the aminotransferases in the liver function test?

A

Alanine aminotransferase ALT
Aspartate aminotransferase AST

26
Q

What does alanine aminotransferase do?

A

Catalyses alanine + a-ketoglutarate > pyruvate + glutamate

27
Q

What does aspartate aminotransferase do?

A

Catalyses asparatate + a-ketoglutarate >oxaloacetate + glutamate

28
Q

Outline deamination

A
  • Liberates amino acid group as free ammonia
  • in liver and kidneys
  • NH3 > NH4+ at physiological pH
29
Q

3 enzymes which deaminate amino acids

A

Amino acid oxidases
Glutaminase
Glutamate dehydrogenase

30
Q

How is urea excreted?

A

In urine via kidneys

31
Q

Management of urea cycle defects

A

Low protein diet
Replace amino acids in diet with keto acids

32
Q

4 properties of urea

A

Non toxic
Water soluble
Chemically inert
High nitrogen content

33
Q

Symptoms of urea cycle defects

A

Vomiting
Lethargy
Irritability
Mental retardation
Seizures
Coma

34
Q

How many enzymes are involved in the urea cycle?

A

5

35
Q

Outline potential toxic effects of ammonia toxicity

A
  • disruption of cerebral blood flow
  • ^pH
  • alters blood brain barrier
  • interference with TCA cycle
  • interference with aa transport and protein synthesis
36
Q

What are the two mechanisms to safely transport ammonia from tissues to liver?

A

Glutamine
Alanine

37
Q

Outline the mechanism of glutamine in the safe transport of ammonia

A
  • ammonia + glutamate > glutamine
  • glutamine transported in blood to liver or kidneys
    glutaminase
  • glutamine > ammonia + glutamate
  • liver: ammonia put into urea cycle
  • kidneys: excreted in urine
38
Q

Outline the mechanism of alanine in the safe transport of ammonia

A
  • transamination - amine group transferred to glutamate
  • amine groups from glutamate > urea cycle
  • pyruvate is transaminated by glutamate > alanine
  • alanine is sent to liver
  • alanine > pyruvate
  • pyruvate > glycolysis
39
Q

What is the heel prick test used to test?

A
  • sickle cell disease
  • cystic fibrosis
  • congential hypothyroidism
  • PKU
  • homocystinuria
40
Q

Cysteine vs cystine vs homocysteine vs homocystine

A

Cysteine - amino acid
Cystine - 2 x cysteine
Homocysteine - made from methionine
Homocystine - 2 x homocysteine

41
Q

Outline the molecular basis of re feeding syndrome

A
  • down regulations enzymes in urea cycle due to low protein intake
  • sudden high protein take overwhelms enzymes
  • ammonia toxicity occurs
42
Q

What is a main property of a glucogenic vs ketogenic amino acid?

A
  • glucogenic: Can be converted to glucose truth gluconeogenesis
  • ketogenic: can be converted into acetyl coA

MEH (23 decks)

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