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2 MEH > 2 Protein & Amino Acid Metabolism > Flashcards

2 Protein & Amino Acid Metabolism Flashcards

1
Q

Identify two major nitrogen containing compounds found in the body

A
  • Amino acids (proteins)
  • Purines + Pyrimidines (DNA / RNA)
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2
Q

Identify three minor nitrogen containing compounds found in the body

A
  • Creatine
  • Neurotransmitters e.g. dopamine
  • Some hormones e.g. adrenaline
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3
Q

What is creatinine?

A

Creatinine is a breakdown product of creatine & creatine phosphate in muscle

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4
Q

What does measuring creatinine levels show us?

A
  • -Indicator for renal function= raised is nephrons damaged
    • Produced at constant rate and filtered via kidneys into urine
    • Provides estimate of muscle mass:
      • Creatinine urine excretion over 24h is directly proportional to muscle mass
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5
Q

What is nitrogen balance?

A

Nitrogen balance is the measure of nitrogen input minus nitrogen output i.e. nitrogen input — nitrogen loss

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6
Q

What is the clinical feature of a positive nitrogen balance?

In what instances in a positive nitrogen balance normal? (3)

A
  • Intake > output

Clinical feature:

  • Increase in total body protein

Normal state in:

  • Growth, pregnancy or adult recovering from malnutrition
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7
Q

What is the clinical feature of a negative nitrogen balance?

In what instances in a negative nitrogen balance normal?

What may cause a negative nitrogen balance? (3)

A
  • Intake < output
  • Net loss of body protein
  • Never normal (trauma, infection, malnutrition)
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8
Q

What is protein turnover?

A

Protein turnover is the balance between protein synthesis and protein degradation

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9
Q

Where do amino acids found in the body come from? (3)

A
  1. De novo amino acid synthesis
  2. Dietary protein
  3. Cellular protein
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10
Q

Provide an example of the following:

  • Glucogenic amino acid
  • Ketogenic amino acid
  • Both ketogenic and glucogenic amino acid
A
  • Glucogenic amino acid: alanine
  • Ketogenic amino acid: leucine
  • Both ketogenic and glucogenic amino acid: isoleucine
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11
Q

When are protein stores mobilised? (ie used for energy)

A

Occurs under extreme stress (starvation)

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12
Q

Describe the hormonal control over the mobilisation of protein reserves

A

Glucocorticoids stimulate the breakdown of protein to be used for energy

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13
Q

In de novo amino acid synthesis, where do the carbon atoms come from?

(Amino acids that can be synthesised de novo are Non-essential amino acids)

A
  • Intermediates of glycolysis (C3)
  • Pentose phosphate pathway (C4 & C5)
  • Krebs cycle (C4 & C5)
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14
Q

In the de novo amino acid synthesis, where does the amino group come from?

A

Amino group provided by:

  • other amino acids by the process of transamination
  • (transfers an amino group to a ketoacid to form new amino acids)*
  • from ammonia
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15
Q

Which compounds are synthesised from tyrosine?

A
  • Catecholamines
  • Melanin
  • Thyroid hormones
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16
Q

Which compound is synthesised from histidine?

A

Histamine

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17
Q

Which compound is synthesised from arginine?

A

Nitric oxide

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18
Q

Which compound is synthesised from cysteine?

A

Glutathione

Hydrogen sulphide (signalling molecule)

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19
Q

Which compounds are synthesised from tryptophan?

A
  • Serotonin (5HT)
  • Melatonin
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20
Q

Which molecules are synthesised from glycine?

A
  • Purines
  • Glutathione
  • Haem
  • Creatine
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21
Q

What has to happen to an amino acid to allow it to be used in oxidative metabolism?

A
  • Removal of amine group
  • carbon skeleton used
    • Once removed nitrogen can be incorporated into other compounds or excreted from body as urea*
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22
Q

What are the two main pathways that facilitate removal of nitrogen from amino acids?

A
  • Transamination
  • Deamination
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23
Q

Explain the process of transamination

A
    • Aminotransferase enzymes
      • use a-ketoglutarate
      • funnel the amino group to glutamate
    • Exception to rule is Aspartate Aminotransferase
      • uses oxaloacetate
      • funnel amino group to aspartate
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24
Q

Which aminotransferase enzymes are measured routinely as part of liver function test?

A
  • Alanine aminotransferase (ALT) which converts alanine to glutamate
  • Aspartate aminotransferase (AST) which converts glutamate to aspartate
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25
Q

High plasma AST and ALT levels are associated with which conditions? (extensive cellular necrosis)

A
  • Viral hepatitis
  • Autoimmune liver diseases
  • Toxic injury
26
Q

Explain the process of deamination

A
  • Liberates amino group as free ammonia (later converted to urea)
  • Mainly occurs in liver & kidney
  • Keto acids can be utilised for energy
27
Q

Several enzymes can deaminate amino acids.

Identify three

A
  • Amino acid oxidases
  • Glutaminase
  • Glutamate dehydrogenase
28
Q

What happens to ammonia at physiological pH?

A

At physiological pH, ammonia (NH3) is rapidly converted to ammonium ion (NH4+)

29
Q

Ammonia (and ammonium ions) are very toxic and must be removed.

How does this occur?

A

Ultimately converted to urea or excreted directly in urine

30
Q

Describe 5 properties of urea

A
  • High nitrogen content
  • Non-toxic
  • Extremely water soluble
  • Chemically inert in humans
  • has osmotic role in kidney tubules
31
Q

What is the urea cycle?

A
  • The urea cycle is a process:
  • occurring in liver
  • involves 5 enzymes
  • It is used to dispose of ammonia

Cycle=inducible NOT regulated

32
Q

Explain how a high/low protein diet affects the urea cycle enzyme levels

A
  • High protein diet induces enzyme levels (up-regulation)
  • Low protein diet or starvation represses enzyme levels (down-regulation)
33
Q

What is refeeding syndrome?

A
  • Refeeding syndrome is a condition:
  • occurs when nutritional support given to severely malnourished patients
  • Ammonia toxicity significant factor (urea cycle down regulated)
34
Q

What are the risk factors for refeeding syndrome?

A
  • BMI < 16
  • Unintentional weight loss > 15% in 3-6 months
  • 10/more days with little or no nutritional intake
35
Q

What are the effects of autosomal recessive genetic disorders caused by deficiency of one of enzymes in the urea cycle? (1 in 30,000 live births)

A
  • Hyperammonaemia
  • Accumulation/excretion of urea cycle intermediates
36
Q

What does the severity of defects in the urea cycle depend on? (2)

A
  • Nature of defect
  • Amount of protein eaten
37
Q

What are the symptoms of genetic disorders due to defects in the urea cycle?

A
  • Vomiting
  • Lethargy
  • Irritability
  • Mental retardation
  • Seizures
38
Q

What is the management for autosomal recessive disorders due to defects in the urea cycle?

A
  • Low protein diet
  • Replace amino acids in diet with keto acids
39
Q

Why do ammonia levels need to be kept (relatively) low? (BLOOD: 25-40 µmol/L)

A
  • Ammonia is readily diffusible and extremely toxic to brain
40
Q

Identify 5 toxic effects of ammonia

A
  • Interference with amino acid transport and protein synthesis
  • Disruption of cerebral blood flow
  • pH effects (alkaline)
  • Interference with metabolism of excitatory amino acid neurotransmitters e.g. glutamate and aspartate
  • Alteration of the blood–brain barrier
41
Q

Two mechanisms are utilised for the safe removal of ammonia from tissues for disposal.

In 4 steps, outline the use of glutamine

A

⇒ Ammonia combines with glutamate to form glutamine

⇒ Glutamine transported in blood to liver /kidneys

⇒ Cleavage by glutaminase to reform glutamate and ammonia

⇒ Ammonia fed into urea cycle (liver) / excreted directly in urine (kidneys)

42
Q

Two mechanisms are utilised for the safe removal of ammonia from tissues for disposal.

In 5 steps, outline the use of alanine

A

⇒ Ammonia combines with pyruvate to form alanine

⇒ Alanine transported in blood to liver

⇒ Conversion to pyruvate by transamination

⇒ Amino group fed via glutamate into urea cycle for disposal as urea

⇒ Pyruvate is used to synthesise glucose

43
Q

Identify 7 clinical conditions which can be detected by the heel prick test.

A
  • Sickle cell disease
  • Cystic fibrosis
  • Congenital hypothyroidism
  • Phenylketonuria (PKU)
  • Homocystinuria
  • Maple syrup urine disease
  • Isovaleric acidaemia (IVA)
44
Q

What is phenylketonuria? (PKU)

A
    • PKU:
      • common inborn error of amino acid metabolism
      • due to an autosomal recessive deficiency in phenylalanine hydroxylase
        • Phenylalanine accumulates in the tissue, plasma & urine
      • presents with phenylketones in urine (musty smell)
45
Q

Outline the treatment of phenylketonuria

A
  • Strictly controlled low phenylalanine diet
  • Avoid artificial sweeteners (contain phenylalanine)
  • Avoid high protein foods such as meat, milk, and eggs
  • Enrich diet w./ tyrosine
46
Q

Identify 5 symptoms of PKU (if left untreated)

A
  • Severe intellectual disability
  • Developmental delay
  • Microcephaly (small head)
  • Seizures
  • Hypopigmentation
47
Q

Illustrate the affected pathways in PKU

A
48
Q

What is homocystinuria?

A
    • Homocystinuria:
      • Autosomal recessive disorder
      • commonly due to a defect in cystathionine β-synthase leading to an inability in breaking down methionine
        • Excess homocystine (oxidised form of homocysteine) is excreted in urine
49
Q

Which tissues/systems are affected in homocystinuria?

A
  • Connective tissue
  • Muscles
  • CNS
  • CVS
50
Q

Outline the treatment of homocystinuria

A
  • Low-methionine diet
  • Avoid: milk, meat, fish, cheese, eggs and nuts
  • Supplements: cysteine, Vit B6, Betaine, B12 & Folate
51
Q

Illustrate the affected pathways in homocystinuria

A

Accumulation of methionine and homocysteine causes symptoms

52
Q

What happens to free amino acids found in the body (what are they used for)?

A
  1. Synthesis- cellular proteins
  2. Energy (glucogenic/ketogenic)
  3. Excreted in urine (urea)
53
Q

List the 9 essential amino acids (cannot be synthesised by the body):

(If Learnt This Huge List May Prove Truly Valuable)

A
  1. Isoleucine
  2. Leucine
  3. Threonine
  4. Histidine
  5. Lysine
  6. Methionine
  7. Phenylalanine
  8. Tryptophan
  9. Valine
54
Q

Under what circumstances are certain amino acids conditionally essential?

A

Times- rapid protein synthesis

eg Pregnancy/children

Arginine,tyrosine,cysteine

55
Q

What coenzyme do all aminotransferases require?

A
  • Pyridoxal phosphate (Vitamin B6 derivative)
56
Q

Where in the body are amino acids processed to be used for energy?

A

Liver

57
Q

How do we treat a patient at risk of developing refeeding syndrome?

A

Re-feed @ 5-10kcal/kg/day

Raise gradually

58
Q

Differentiate between Cysteine, Cystine, Homocysteine and Homocystine

A
59
Q

What and why are some of the symptoms of homocystinuria and Marfan’s syndrome similar?

A
  • Excess homocysteine- damages collagen and elastic fibres (binds to lysine residues in proteins)
  • eg Lens dislocation and skeletal deformities
60
Q

How do the symptoms of marfan’s and homocystinuria differ?

A

Metabolites of methione=toxic to neurones

NEUROLOGICAL DYSFUNCTION not seen in Marfan’s

2 MEH (18 decks)

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