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Metabolism and Biochem > Proteins and Amino acids > Flashcards

Proteins and Amino acids Flashcards

1
Q

What are 4 uses for amino acids?

A

1) Protein synthesis
2) Energy and gluconeogenic substrates
3) Neurotransmitters (eg. GABA)
4) Non-peptide hormones (eg. thyroxine, epinephrine)
5) Heme
6) Nucleotides

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2
Q

_____ of the dry matter in our cells are made of proteins yet there is no large reservoir of amino acids.

A

~50%

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3
Q

What are 3 ways we get amino acids?

A

1) Dietary proteins (exogenous)
2) Breakdown of own proteins (endogenous)
3) Biosynthesis

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4
Q

What is cystinuria?

A

Failure in reabsorption and uptake of cystine, ornithine, arginine, lysine (COAL)

→ cystine kidney stones

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5
Q

What is Hartnup’s disease?

A

Failure in reabsorption and uptake of neutral amino acids (eg. Tryptophan, phenylalanine)

→
1) Cerebellar ataxia (lack of coordination and involuntary movement)
2) Pellagra-like symptoms (eg. skin lesions, dermatitis)

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6
Q

True or false:
Px with Hartnup’s disease or Cystinuria exhibit hyperaminoacidemia.

A

False.
Both exhibit hyperaminoaciduria
(kidney can filter from blood but cannot reabsorb → only accumulate in urine)

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7
Q

What are 3 states of nitrogen balance?

A

1) Nitrogen balance (intake=ouput)
- only when dead

2) Positive N balance (intake > output)
- eg. growth, pregnancy, refeeding

2) Negative N balance (intake < output)
- eg. starvation, senescence, metabolic stress

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8
Q

What happens to amino acids in excess of those needed for bodily function?

A

Deaminated into ketoacids(oxoacids)
- remove NH3 group to release NH4

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9
Q

How does oxidative deamination occur?

A

L-Glutamate → α-Keto Glutarate
- via L-Glutamate Dehydrogenase
- can use both NAD+ and NADP+ as cofactors → NADH NADPH
- H2O → NH4+
- reversible

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10
Q

True or false:
Oxidative deamination is a reversible rxn.

A

True

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11
Q

What are the co-factors needed for oxidative amination?

A

Either NAD+ or NADP+
- also H2O

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12
Q

What are the products of oxidative deamination?

A

1) α-Keto Glutarate
2) NADH/NADPH
3) NH4+

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13
Q

Which enzyme catalyses oxidative deamination?

A

L-Glutamate Dehydrogenase

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14
Q

What is the enzyme and cofactor needed for transamination?

A

Enzyme: Transaminase (aminotransferase)

Cofactor: PLP (from Vit. B6)

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15
Q

Where does Pyridoxal phosphate (PLP) come from?

A

Vit. B6

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16
Q

True or false:
Transamination is a reversible rxn.

A

True

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17
Q

How is Aspartate transaminated?

A

Aspartate → Oxaloacetate
α-Ketoglutarate → Glutamate
via AST (aspartate aminotransferase)

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18
Q

How is Alanine transaminated?

A

Alanine → Pyruvate
α-Ketoglutarate → Glutamate
via ALT (alanine aminotransferase)

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19
Q

How does transdeamination occur?

A

Coupling aminotransferase to Glutamate dehydrogenase

  • amino group from amino acid
    → glutamate (transamination)
    → NH4+ (oxidative deamination
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20
Q

What are 2 functions of transamination?

A

1) Funnel amino groups on amino acids into glutamine for conversion into ammonia

2) Synthesis of non-essential amino acids

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21
Q

What are ALT and AST levels used for?

A

Assessing tissue damage
- released from damaged cells into blood
- especially muscle, liver, brain

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22
Q

What is a schiff base?

A

An aldimine linkage between:
1) Aldehyde group of PLP
2) ɛ̝-amino group of lysine

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23
Q

Why is PLP essential for transamination?

A
  • links α-amino acid group to transaminase enzyme
    → facilitate transfer of amino group to the keto acid substrate
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24
Q

What are the 6 steps of transamination?

A

1) amino acid → Transimination
2) Tautomerisation
3) Hydrolysis → ketoacid
4-6) Reverse

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25
Q

What are 4 non-oxidative deamination deaminases?

A

1) Ammonia lyases (α-deaminases)
- L-Aspartate → Fumarate + NH4+

Specific:
1) Serine dehydratase → Pyruvate + NH4+

2) Threonine dehydratase → α-ketobutyrate + NH4+

3) Cysteine desulfhydrase → Pyruvate + NH4+ + H2S

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26
Q

At physiological pH, ammonia (can/cannot) freely cross the cell membrane.

A

Cannot (ion trapping)
- 99% of ammonia is protonated (pKa = 9.3)

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27
Q

What determines whether oxidative deamination occurs in forward or reverse?

A

ATP/GTP: Forward → α-KG
ADP/GDP: Reverse → Glutamate

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28
Q

What does glutamine synthetase do?

A

Add another amino group onto L-glutamate
L-glutamate → L-glutamine
- req. (i) Mg2+ (ii) ATP

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29
Q

What does Glutaminase/Glutamine Deaminase do?

A

Remove 1 amino group from glutamine → glutamate

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30
Q

How is NH4+ excreted in urine through the ion-trapping mechanism?

A

NH4+ “loading” (intracellular)
1) NH4+ + α-KG → Glutamate (GDH reverse rxn)

2) NH4+ + Glumate → Glutamine (Glutamine synthetase)

3) Glutamine transported out of cells → Blood → Liver/Kidney

NH4+ “off-loading” (eg. Kidney)
4) Glutamine → Glutamate + NH4+ (Glutaminase)

5) Glutamate → α-KG + NH4+ (GDH)

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31
Q

Which enzyme is responsible for the toxicity of ammonia?

A

GDH (glutamate dehydrogenase)
- depletion of NADH/NADPH from reverse rxn to L-glutamate

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32
Q

Which organ does the urea cycle primarily take place?

A

Liver

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33
Q

Which enzymes of the urea cycle are in the (i) mitochondria and (ii) cytosol

A

i) Mitochondria:
1) Carbamoyl Phosphate (CP) Synthetase I

2) Ornithine Transcarboxylase (OTC)

ii) Cytosol
1) Arginosuccinate Synthase (ASS)
2) Arginosuccinate lyase (ASL)
3) Arginase

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34
Q

How is the urea cycle regulated?

A

1) Compartmentalisation (OTC and CP synthetase I in mitochondria)

2) Transcriptional regulation of relevant enzymes

3) Feed-forward activation

4) Allosteric control

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35
Q

CP Synthetase I is responsible for the __________ step of the urea cycle, is ________-dependent and allosterically activated by ________________.

A

Rate-limiting step
Ammonia dependent
Allosterically activated by N-Acetylglutamate

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36
Q

How is N-Acetylglutamine produced?

A

Glutamate → N-Acetylglutamine
- via Acetylglutamate synthase (N-acetyl transferase)
- Acetyl CoA → CoASH
- allosterically activated by Arginine

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37
Q

Why do we excrete urea instead of ammonia?

A

Urea is more soluble in water

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38
Q

What are the net substrates and products of urea synthesis (excluding water)

A

NH4+ + HCO3- + Aspartate
→
Urea + Fumarate + H+

(3 ATP → 2 ADP + AMP + 2Pi + PPi)

39
Q

True or false:
Any urea enzyme defect results in hyperammonemia.

A

True

40
Q

What hyperammonemia disease and enzyme for:
Urine Ornithine: ↓
Blood Citrulline: ↓
Blood Arginine: ↓

A

Type 1 Hyperammonemia
- CP Synthetase I
(early in cycle)

41
Q

What hyperammonemia disease and enzyme for:
Urine Ornithine: ↑
Blood Citrulline: ↓
Blood Arginine: ↓

A

Hyperammonemia Type II
- Ornithine Transcarbamoylase (OTC)

(accumulation of ornithine)

42
Q

What hyperammonemia disease and enzyme for:
Urine Ornithine: -
Blood Citrulline: ↑ (>1000 uM)
Blood Arginine: ↓

A

Citrullinemia
- Argininosuccinate synthetase (ASS)

(defect right above citrulline → ↑substrate)

43
Q

What hyperammonemia disease and enzyme for:
Urine Ornithine: -
Blood Citrulline: ↑ (> 200uM)
Blood Arginine: ↓

A

Argininosuccinic aciduria/acidemia
- Argininosuccinate Lyase (ASL)

(further downstream from citrulline → ↓accumulation than ASS problem: Citrullinemia)

44
Q

What hyperammonemia disease and enzyme for:
Urine Ornithine: -
Blood Citrulline: -
Blood Arginine: ↑

A

Argininemia
- Arginase

(only one that causes ↑Arg)

45
Q

What 3 enzymes are involved in ammonia assimilation?

A

1) Glutamine synthetase
2) Glutamate dehydrogenase (GDH)
3) Carbamoyl Phosphate synthetase (CP synthetase)

46
Q

What is the difference between the potential of ketogenic and glucogenic amino acids?

A

Ketogenic: can from ketone bodies

Glucogenic: can form glucose

47
Q

What are the 3 ketone bodies?

A

1) Acetoacetic acid
2) ß-Hydroxybutyric acid
3) Acetone

48
Q

Disruption of the conversion of branched-chain amino acids Leucine and Isoleucine into Acetoacetate, and Acetyl-CoA and Succinyl CoA, respectively is known as what disease?

A

Maple Syrup Urine disease
- darkening of urine → look like maple syrup

49
Q

What is the glucose-alanine cycle?

A

Key method of removing ammonia from muscles and regenerate glucose in liver for glycolysis back in muscles

1) Urea packages into Alanine via (a) Ox decarb (b) transamination

2) Alanine transported to Liver
3) Alanine converted to pyruvate via ALT and used for (a) urea cycle (b) gluconeogenesis

4) Glucose transported back to muscle
5) Glucose used in glycolysis to generate pyruvate → alanine

50
Q

Why do muscles produce so much ammonia?

A

Need energy
→ utilise Adenylate Kinase to produce ATP from ADP

BUT also produces AMP (need to deaminate)
- via Adenylate deaminase → IMP

51
Q

Which of the amino acids are strictly ketogenic?

A

Leucine and Lysine

52
Q

Hyperammonemia patients and ammonia toxicity can be treated with ______ and _______

A

Glucose and Arginine

53
Q

What are the 9 essential and 1 semi-essential amino acids?

A

PVT TIM HALL
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Arginine (semi)
Leucine
Lysine

54
Q

What are 4 types of biochemicals synthesised in glutamate metabolism?

A

1) Non-essential amino acids
- via transamination (eg. aspartate, alanine)
- glutamine synthetase (glutamine)
- redox reactions (eg. ornithine, proline)

2) From α-KG
- via GDH

3) Glutathione

4) GABA

55
Q

What are 5 types of biochemicals synthesised in glutamine metabolism?

A

1) Synthesis from Glutamate
- glutamine synthetase

2) Glutamate (hydrolysis)

3) Transamidation
- Fructose-6-P → Glusoamine-6-P via transamidase
- Glutamine → glutamate

4) Purines and Pyrimidines

5) CTP and GMP
- via respective synthetases

56
Q

What are 4 types of biochemicals synthesised in Aspartate and Asparagine metabolism?

A

1) Oxaloacetate → Aspartate
- Transamination

2) Asparagine → Aspartate
- via Asparaginase

3) Asparagine
- Aspartate → Aspargine
- Asparagine synthetase

4) Purines and pyrimidines

57
Q

Which phenyl-ketones are elevated in PKU?

A

1) Phenylethylamine
2) Phenylacetate
3) Phenyllactate
(2 and 3 from Phenylpyruvate)

58
Q

What are the enzymes affected in Phenylketouria?

A

1) Phenylalanine hydroxylase (classical)
2) Dihydropteridine reductase (non-classical)

59
Q

What are 2 ways Tetrahydrobiopterin (BH4) can be synthesised?

A

1) From GTP
2) From Dihydrobiopterin (BH2)

60
Q

Where is tyrosine converted into thyroxin?

A

Thyroid

61
Q

Where is tyrosine converted to melanin?

A

Melanocytes

62
Q

Where is tyrosine converted to DOPA?

A

1) Melanocytes
2) Adrenal medulla/neurons

63
Q

In which condition is the enzyme phenylalanine hydroxylase affected?

A

PKU (Classical)

64
Q

In which condition is the enzyme DHP reductase affected?

A

PKU (non-classical)

65
Q

In which condition is the enzyme Fumarylacetoacetate hydrolase affected?

A

Tyrosinemia Type I (Tyrosinosis)

66
Q

In which condition is the enzyme Tyrosine aminotransferase (TAT) affected?

A

Tyrosinemia Type II

67
Q

In which condition is the enzyme Homogentisate oxidase affected?

A

Alcaptouria

68
Q

In which condition is the enzyme Tyrosinase affected?

A

Albinism

69
Q

Are all cases of albinism caused by defected tyrosinase?

A

No. Some by unknown number of genetic loci encoding for genes involved in melanin synthesis

70
Q

How do pathological Tyrosinase defects present?

A

Albinism:
milky white skin, white hair, red eyes

71
Q

How can classical PKU be treated?

A

1) Supply tyrosine
2) Reduce dietary phenylalanine

72
Q

How are patients with Parkinson’s treated?

A

DOPA (not dopamine → cannot cross BBB)

73
Q

Why are there side effects to administering only DOPA for Parkinson’s px and how are they prevented?

A

DOPA carboxylases outside CNS → dopamine → AEs

must administer with DOPA analogs (eg. carbidopa, methyldopahydrazine) → inhibit DOPA decarboxylase

74
Q

How is L-Citrulline produced?

A

L-Arginine → L-Citrulline
- via NO synthetase
- NADPH + H+ → NADP+
- O2 → NO

75
Q

What are 4 functions of NO?

A

1) Vasodilation (via smooth muscle relaxation)
2) Prevent platelet aggregation
3) Nitrate synthesis
4) Mediates tumoricidal and bacteriocidal action of macrophages
5) NT in brain

76
Q

What is the mode of action of Sildenafil (Viagra)?

A

1) Potentials vasodilation
2) Inhibits cGMP phosphodiesterase

77
Q

What are 5 non-protein products synthesised from amino acids?

A

1) Purines
2) Pyrimidines
3) Porphyrin and heme (Gly)
4) Glutathione (Gly, Glu, Cys)
5) Creatine and creatinine (Gly, Arg, Met)
6) S-Adenosyl Methionine (Methionine)
7) Carnitine (Lys, Met)
8) Serotonin, melatonin, NAD+ (Try)
9) T3/4, melanin, catecholamines (Phe, Tyr)

78
Q

How are primary amines formed?

A

Decarboxylation via amino acid darcarboxylase

79
Q

What are 3 functions of histamine?

A

1) Vasodilator
2) Inflammatory mediator in HS rxn
3) Stimulates pepsin and acid secretion in stomach

80
Q

What are the function of GABA?

A

Inhibitory NT (neuronal regulator)

81
Q

What is Huntington’s chorea?

A

Inherited disorder
- degeneracy of GABA-producing cells/GAD deficiency
→ low GABA in corpus striatum
→ continuous involuntary movement

82
Q

What are 2 functions of serotonin?

A

1) Vasoconstriction
2) NT in sensory mechanisms

83
Q

What is the function of dopamine?

A

Inhibitory NT

84
Q

What is the function of tyramine?

A

Hypertensive agent

85
Q

What are 3 polyamines?

A

1) Putrescine
2) Spermidine
3) Spermine

86
Q

What are 4 functions of polyamines?

A

1) Cell growth and proliferation
2) Stabilise and package DNA
3) Stimulate DNA/RNA synthesis
4) Regulates enzyme/protein synthesis
5) Platelet aggregation
6) Lipolysis

87
Q

The synthesis of polyamines (eg. Putrescine, Spermidine, Spermine) require which amino acid?

A

Methionine

88
Q

What is the function of Creatine?

A

Energy storage
- can be (de)phosphorylated via creatine kinase → creatine phosphorylation (high energy)
- substrate-level ATP production when needed

89
Q

In which organs is glycine transaminidinase or guanidinoacetic acid synthesis located?

A

Kidney and pancreas

90
Q

Why is ATP not a good choice for storage as an energy reserve?

A

ATP affects a lot of reactions
(allosteric regulation)

91
Q

Where does Creatine synthesis via methylation from guanidinoacetic acid occur?

A

Liver and pancreas

92
Q

Where is Creatine kinase found?

A

Muscle and brain

93
Q

What is the principal energy storage chemical in muscles?

A

Creatine phosphate

94
Q

What are the nitrogenous substances excreted by humans in order of abundance?

A

1) Urea (30g)
2) Creatinine (1-1.8g)
3) NH4+ (0.7g)
4) Uric acid (0.5-1g)

Metabolism and Biochem (8 decks)

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