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MEH > Protein and AA metabolism > Flashcards

Protein and AA metabolism Flashcards

1
Q

what is N equilibrium

A

intake = output
normal state adults
no change in body proteins

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2
Q

what is positive N balance

A

intake > output
- increase body protein
- pregnancy, growth ,recovery from malnutrition

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3
Q

what is negative N balance

A

intake < output
- loss of body protein
- trauma, infection, malnutrition

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4
Q

what is the average dietary protein intake for 70 Kg male

A

16g N

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5
Q

what is the average amount of body proteins for 70 Kg male

A

2Kg N

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6
Q

what is the average weight of amino acid pool for 70 Kg male

A

16g N

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7
Q

what is the average weight of nitrogen containing compounds for 70 Kg male

A

60g N

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8
Q

what is the average weight of loss skin, hair, nails for 70 Kg male

A

2g N

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9
Q

what is the average weight of n waste products for 70 Kg male

A

14g N

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10
Q

what is protein turnover

A

proteins undergoing continuous breakdown and resynthesis

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11
Q

what is the half life of a protein

A

80g

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12
Q

when are protein reserves metabolised and how is this controlled

A

occurs during extreme stress (starvation)
hormonal control

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13
Q

describe how insulin and growth hormone affet protein synthesis and protein degradation

A
  • increases synthesis
  • decreases degradation
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14
Q

describe how gluocorticoids (cortisol ) affects protein synthesis and degradation

A
  • decreases synthesis
  • increases degdradation
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15
Q

what is cushing’s syndrome

A

excessive breakdown of protein from excess cortisol
weakens skin structure leading to striae

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16
Q

what type of amino acids can the body synthesise

A

non- essential

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17
Q

where do the carbon atoms come from for AA synthesis

A
  • intermediates of glycolysis
  • PPP
  • krebs
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18
Q

where does the amino group come from for amino acid synthesis

A
  • provided by other AAs (transamination)
  • ammonia
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19
Q

what does tyrosine produce

A
  • catecholamines
  • melanin
  • thyroid hormone
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20
Q

what does cysteine produce

A
  • hydrogen sulphide
  • glutathione
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21
Q

what does tryptophan produce

A
  • nicotinamide
  • serotonin
  • melatonin
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22
Q

what does histidine produce

A
  • histamine
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23
Q

what does glutamate produce

A
  • GABA
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24
Q

what does arginine produce

A

nitric oxide

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25
Q

what does serine produce

A

sphingosine

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26
Q

what does glycine produce

A
  • purines
  • glutathione
  • haem
  • creatine
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27
Q

why must excess AAs be broken down

A

they cannot be stored or excreted so broken down into small molecules

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28
Q

where is the major breakdown site of AAs

A

liver

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29
Q

what do all pathways of breakdown of AAs have in common

A
  • C atoms converted to intermediates of carb and lipid metabolism
  • removal of NH2 group
  • N atoms usually converted
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30
Q

why is the removal of the amino group necessary in breakdown of AAs

A

so carbon skeleton can be used for metabolism and N can be incorporated into other compound or excreted as urea

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31
Q

what are the two methods of removing amino groups from AAs

A
  • transamination
  • deamination
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32
Q

describe the process of transamination

A

transferring one amino group from one AA to another using and forming keto acids usually a-ketoglutarate
AA1 + keto acid 2 –> AA2 + keto acid 1

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33
Q

what are the enzymes involved in transamination

A
  • alanine aminotransferase (ALT)
  • aspartate aminotransferase (AST)
34
Q

what does the ALT enzyme do

A

converts alanine and a-ketoglutarate to pyruvate and glutamate

35
Q

what does the AST enzyme do

A

aspartate and a-ketoglutarate –> oxalacetate and glutamate

36
Q

why are ALT and AST levels measured in blood and when would they be high

A

check liver function
levels high in necrosis :
- viral hepatitis
- autoimmune liver disease
- toxic injury

37
Q

what co-enzyme do ALT and AST need

A

pyridoxal phosphate which is a B6 derivative

38
Q

what is deamination

A

the process of liberating the amino group to free ammonia

39
Q

where does deamination occur

A

in liver and kidney

40
Q

what enzymes are involved in deamination

A
  • L and D amino acid oxidases
  • glutaminase
  • glutamate dehydrogenase
41
Q

why do humans have high activity of D amino acid oxidase

A

D amino acids are found in plant and bacteria cells so enter through diet and must not be used for protein synth as will form abnormal proteins as human proteins are in L form so change them into keto acids

42
Q

what does glutaminase do

A
  • high specificity
  • converts glutamine to glutamate and ammonia
43
Q

what does glutamate dehydrogenase do

A
  • high specificity
  • converts glutamate + NAD + H2O –> a-ketoglutarate + NH4 + NADH + H+
44
Q

what is PKU

A

phenylketonuria

45
Q

what is the defective enzyme in PKU
what is its normal function

A

phenylalanine hydroxylase
- normal function: converts phenylalanine –> tyrosine

46
Q

what accumulates in PKU and what does this produce

A

phenylalanine accumulates in blood so metabolised by other pathways to produce phenylketones in urine (musty smell)

47
Q

what are the symptoms of PKU

A
  • severe intellectual disability
  • developmental delay
  • microcephaly (small head)
  • seizures
  • hypopigmentation (tyrosine cannot produce melanin)
48
Q

how is PKU tested for

A

heel prick test at birth
test for conc of phenylalanine

49
Q

how is PKU treated

A
  • diet with low phenylalanine but high tyrosine
50
Q

what is homocystinuria

A

a defect in the cystathione-β-synthase
- normally converts homocysteine to cystathione which produces cysteine

51
Q

where does homocyteine come from

A

breakdown of methionine

52
Q

how is homocystinuria detected

A

elevated levels of homocysteine and methionine in plasma and the presence of homocystine (oxidised homocysteine) in urine

53
Q

what are the symptoms of homocystinuria

A

damage to connective and muscle tissue and damage to CNS and CVS

54
Q

how is homocystinuria treated

A

low methionine diet
avoid milk, fish, eggs , cheese, nuts
supplement with cysteine, vitamin B 6 and 12 and folate

55
Q

what is a glucogenic amino acid

A

used to synthesise glucose

56
Q

give two examples of glucogenic AA

A

alanine and cysteine

57
Q

what is a ketogenic AA

A

used to synthesise FA or ketone bodies

58
Q

give two examples of ketogenic AA

A

lysine and leucine

59
Q

give two examples of AA that are both ketogenic and glucogenic

A

tyrosine and tryptophan

60
Q

why must ammonia be quickly removed from cells

A

it is toxic

61
Q

what is ammonia converted to to be removed

62
Q

how does ammonia affect the CNS

A
  • CNS sensitive to high ammonia (hyperammonaemia)
  • blurred vision
  • slurred speach
  • tremors
  • coma
63
Q

why is the CNS sensitive to high ammonia

A

ammonia reacts with a-ketoglutarate which essentially removes it from the TCA cycle so disrupts energy production and CNS dependent on glucose mainly
- ammonia also affects ph

64
Q

what are the toxic affects of ammonia

A
  • interference with AA transport and protein synth
  • disruption of cerebral blood flow
  • affect pH
  • interefere with metabolism of excitatory NTs
  • alteration of blood brain barrier
  • interference of TCA cycle (a-ketoglutarate)
65
Q

where is ammonia detoxified

66
Q

what are the two mechanisms of transporting ammonia from other tissues to the liver for detoxification

A
  • glutamine synthesis
  • alanine synthesis
67
Q

how does glutamine synthesis work for transporting ammonia and using what enzyme

A

ammonia combined with glutamate –> glutamine
enzyme: glutamine synthase

transported to liver cleaved into glutamate and NH3
enzyme: glutaminase

68
Q

how does alanine synthesis work for transporting ammonia and using what enzyme

A

amine groups transferred to glutamate by transamination making pyruvate then pyruvate transaminated to alanine which is transported to the liver

  • converted back to pyruvate and glutamate
    enzyme: alanine aminotransferase
  • glutamate fed into urea cycle
    pyruvate for glucose
69
Q

why can urea be excreted in urine

A

water solule
non-toxic
high N content so effective

70
Q

where is urea synthesised and then transported to

A

liver
kidney

71
Q

what two places does the urea cycle occur in

A

cytoplasm
mitochondria

72
Q

what enzyme if involved in the urea cycle and what does it do

A

glutamate dehydrogenase
converts glutamate into aspartate and NH4

73
Q

what are two necessary reactant for urea cycle

74
Q

how are the enzymes in urea cycle regulated

A

inducible so on an as needed basis
- high protein diet induces
- low protein not induced

75
Q

what do defects in the urea cycle cause

A
  • hyperammonaemia
  • accum of urea intermediates
76
Q

what are the symptoms of an autosomal recessive defect in urea cycle

A

vomitting
lethargy
irritability
intellectual disability
seizures
coma

77
Q

how are defects in urea cycle managed

A

low protein diet
replace amino acids with keto acids

78
Q

what is creatinine

A

the breakdown product of creatine and creatine phosphate

79
Q

what does creatinine give and indication of

A

muscle mass as produced at constant rate proportional to muscle mass

80
Q

where is the creatinine excreted

81
Q

why is creatinine measured

A

test of renal function
- if high in plasma and low in urine kidney is damaged

MEH (12 decks)

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