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APO510 - MEDICAL BIOCHEMISTRY > WEEK 5: Amino acid metabolism > Flashcards

WEEK 5: Amino acid metabolism Flashcards

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USMLE® Step 1 flashcards
1
Q

what are amino acids?

A

Monomeric units for proteins

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2
Q

what is the main source of nitrogen in the body?

A

dietary protein

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3
Q

what compounds contain nitrogen?

A

haem, creatine, purines and pyrimidines

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4
Q

what happens to excess dietary amino acids?

A

not required for protein synthesis can’t be stored (in mammals) & aren’t excreted so are converted to energy metabolites

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5
Q

what are the major metabolic fuels?

A

glucose and fatty acids

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6
Q

what percentage of energy requirements come from amino acids (in humans)?

A

10-25%

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7
Q

what are 2 sources of amino acids in the amino acid pool?

A

dietary protein digestion and synthesis of non-essential amino acids

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8
Q

what are 2 utilisation factors of amino acid pool?

A

go over slide 5 yellow boxes

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9
Q

what are essential amino acids?

A

cannot be synthesized by the body; obtained via diet

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10
Q

what are non-essential amino acids?

A

can be synthesized by the body

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11
Q

what are glucogenic amino acids?

A

catabolism yields pyruvate or an intermediate of the citric acid cycle

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12
Q

what are ketogenic amino acids?

A

yields acetoacetate, acetyl CoA or acetoacetyl CoA

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13
Q

what do glucogenic amino acids produce when broken down?

A

carbon skeletons broken down to glucose precursors

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14
Q

what do ketogenic amino acids produce when broken down?

A

carbon skeletons broken down to ketone body or fatty acid precursors

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15
Q

where is the major site of aa catabolism?

A

liver

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16
Q

what is the first stage of aa catabolism?

A

Deamination/Transamination– removal and conversion of amino group to ammonia or amino group of aspartate

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17
Q

what is the second stage of aa catabolism?

A

Incorporation of nitrogen from ammonia/aspartate to urea

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18
Q

what is the third stage of aa catabolism?

A

Conversion of amino acid carbon skeletons (a-keto acids) to one of the 7 common metabolic intermediates

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19
Q

go over and understand slide 9 diagram

A
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20
Q

what is the name of the enzyme responsible for the removal of the amino group in the initial stages of catabolism?

A

aminotransferases - these are specific for each amino acid.

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21
Q

what does the aminotransferase require as a coenzyme?

A

pyridoxal phosphate (vitamin B6)

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22
Q

slide 11 - just learn the bullet points

A
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23
Q

slide 12 ???

A
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24
Q

what are the 2 isomeric forms that amino acids occur in?

A

L- or D-

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25
Q

which isomeric form of amino acids do animals utilise?

A

L-AA

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26
Q

why are D-AAs broken down?

A

D-AA’s can interfere with metabolism of L-AA’s

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27
Q

what enzyme breaks D-AAs down?

A

D-amino acid oxidase (D-AAO)

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28
Q

Catabolism of glucogenic amino acids
produces…(6)

A

pyruvate
oxaloacetate,
a-ketoglutarate
fumerate or
succinyl-CoA.

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29
Q

slide 15 - what happens and what enzyme? vit B6 is required )

A
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30
Q

what is aspartate converted to?

A

oxaloacetate via transamination

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31
Q

what enzyme is required to convert aspartate?

A

Aspartate aminotransferase (AST). requires B6

32
Q

what is asparargine converted to? what enzyme? slide 17

A
33
Q

how can asparagine be used in the treatment for leukaemia patients?

A
34
Q

what is required for the urea cycle?

A

Glutamate and glutamine are required for the Urea Cycle.

35
Q

why is glutamate a special amino acid?

A

can be formed or degraded by aminotransferases or by glutamate dehydrogenase (mitochondrial enzyme). both reactions are reversible

36
Q

slide 18

A
37
Q

what is oxidative deamination?

A

removal of amino group. Oxygen is being put where the ???what group is. also rpoduces NH4+.

38
Q

slide 19 - is nad(p) h a product or needed for reaction?

A
39
Q

what is glutamine?

A

Glutamine is a non-toxic, transport form of ammonia from the peripheral tissues (especially important in brain)

40
Q

how is glutamine produced? what does it require?

A

In peripheral tissues glutamate is converted to glutamine – Glutamine synthetase enzyme. Requires ATP and free ammonia.

41
Q

how is glutamine converted back to glutamate?

A

by enzyme glutaminase - water is needed and ammonia is released

42
Q

how is a-ketoglutarate produced?

A

through catabolism of both glutamine and glutamate

43
Q

methionine is cyclic - what does that mean?

A
44
Q

what is methionine convertd into?

A

homocysteine

45
Q

what are the 2 “fates” of homocysteine?

A
  1. can be converted back to methionine by methionine synthase.
  2. degraded further into cystiene
46
Q

Catabolism of ketogenic amino acids produces…(3)

A

Acetyl-CoA
Acetoacetate
Acetoacetyl-CoA

47
Q

what are the 2 ketogenic amino acids?

A

leucine and lysine. Both are essential

48
Q

what is glucogenesis?

A
49
Q

what is ketogenesis?

A
50
Q

what is phenylanine converted to?

A

tyrosine

51
Q

what is required in the conversion of phenylanine?

A

phenylalanine hydroxylase

52
Q

what is tyrosine broken down into?

A

Hydroxyphenylpyruvate

53
Q

what is Hydroxyphenylpyruvate broken down into?

A

homogentisate

54
Q

what is Phenylketonuria (PKU)?

A

Autosomal recessive disorder,
high levels of Phenylalanine hydroxlase, low levels of tyrosine

55
Q

what occurs if Phenylketonuria (PKU) is left untreated?

A

If untreated, leads to permanent intellectual disability, seizures, delayed development, behavioural problems, & psychiatric disorders

56
Q

how is Phenylketonuria (PKU) treated?

A

amino acid restriction via low-protein diet, avoid aspartame, supplementation with Tyrosine, monitor blood

57
Q

what are the branched chain amino acids?

A

Valine, Leucine, Isoleucine

58
Q

how are Valine, Leucine, Isoleucine broken down first step

A

transamination

59
Q

how are Valine, Leucine, Isoleucine broken down - second step

A

oxidative decarboxlyation

60
Q

go over slide 36 third step!! need to know

A
61
Q

maple syrup urine disease, go over

A
62
Q

how is MSUD treated?

A
63
Q

why is ammonia converted?

A

Ammonia is produced as a result of amino acid degradation and is potentially toxic – required to be converted into a non-toxic form

64
Q

what are amino acids broken down into basically?

A

NH3 is TOXIC
Carbon skeleton

65
Q

what is NH3 detoxified into?

A

urea in the urea cycle in the liver

66
Q

slide 42

A
67
Q

where does the breakdown of amino acids occur? double check

A

muscle, peripheral tissues

68
Q

slide 44

A
69
Q

what does alanine do?

A

main ammonia transporter produced in muscle due to the high levels of pyrvuate generated

70
Q

chemical formula of urea contains 2 N atoms. How are they donated?

A

One of the N atoms of urea is donated by ammonia (GDH & Glutaminase)

the second N atom is donated by aspartate

71
Q

What 2 roles does glutamate play in the formation of NH3 for urea cycle?

A

Transamination: the amino group of an amino acid is transferred to α-ketoglutarate to form glutamate

Oxidative deamination by Glutamate dehydrogenase forms free ammonia

72
Q

learn the reaction of the urea cycle, write down steps - slide 48

A
73
Q

how many enzymatic reactions of urea cycle?

A

5

74
Q

what are the 5 enzymatic reactions of urea cycle?

A

2 mitochondria
3 cytosolic

75
Q

what is a rate limiting step of the urea cycle?

A

the requirement of hydrolysis of 2 ATP

76
Q

go up to slide 54

A
77
Q

what indicates that the urea cycle needs to be regulated?

A

Increase in arginine indicates substrate availability i.e. NH3

APO510 - MEDICAL BIOCHEMISTRY (12 decks)

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