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MET1 > Nitrogen Metabolism > Flashcards

Nitrogen Metabolism Flashcards

1
Q

Where does nitrogen come from? How is it stored?

A 
From food (only way)
It cannot be stored
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2
Q

Why do amino acids have different properties?

A
  • Amino acids have different properties; depending on their side chains
  • Some are essential amino acids!
  • Some are conditionally essential amino acids (ex. Arginine)!
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3
Q

Why do we need amino acids?

A
  • Amino acids are need both as amino acids and as building blocks for proteins
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4
Q

What are the other biochemical functions of amino acids?

A
  • As intermediates in other metabolic cycles

- As building blocks of other chemicals (or are themselves used as signalling molecules)

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5
Q

What can tyrosine (phenylalanine) be metabolised to?

A

Melanin, dopamine, adrenaline, noradrenaline, thyroxine

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6
Q

What can tryptophan be metabolised to?

A

Serotonin, melatonin

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7
Q

What can arginine be metabolised to?

A

Nitric oxide

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8
Q

What can histidine be metabolised to?

A

Histamine

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9
Q

What can glycine, glutamate and aspartate be metabolised to?

A

Are used directly as neurotransmitters

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10
Q

What is transamination and what is it catalysed by?

A
  • Process by which new amino acids can be made by using the carbon skeleton of other amino acids and transferring a new side chain on it.
  • Catalysed by transaminase enzymes (imp. in liver)
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11
Q

What keto acids correspond to alanine, glutamate and aspartate?

A

Pyruvate, alpa-ketoglutrate, oxaloacetate

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12
Q

What intermediary is required in transamination and from where is it derived?

A
  • Requires an intermediary called:
    o Pyridoxal phosphate (derived from vitamin B6)
    o Completely reversible!
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13
Q

What are the symptoms of vitamin B6 deficiency?

A
  • Skin inflammation
  • Cardiovascular problems
  • Depression
  • Anaemia
  • Neurological degeneration
  • Dementia
  • Fatigue
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14
Q

What are glucogenic amino acids?

A
  • Glucogenic – can be converted into glucose by gluconeogenesis and can feed into the TCA cycle as pyruvate or one of intermediates.
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15
Q

What are ketogenic amino acids?

A
  • Ketogenic - can be converted to ketone bodies and feed TCA cycle mostly by being converted to acetyl coA or acetylacetate.
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16
Q

Can amino acids be both glucogenic and ketogenic?

A

Yes!

17
Q

How is ammonia generated? Why is this a problem? How is it excreted?

A
  • During these reaction that produce TCA intermediaries (deamination), the amino group is no longer required, and is given off in the form of ammonia.
  • Ammonia is toxic and highly reactive and alkaline so can alter pH.
  • Excess ammonia is removed from the body to prevent its build up.
    o Excreted in the form of UREA – in the UREA cycle.
18
Q

What enzyme may be used to convert glutamate to alpha-glutamate?

A

Glutamate dehydrogenase

19
Q

What is glutamine? Why is it important? How is it formed? What can it be converted to, and what does this produce?

A
  • Glutamine is by far the most abundant amino acid in the body
  • Glutamate is an important neurotransmitter; present in more than half of nervous tissues.
  • Formed during the metabolism of glucose and amino acids.
  • Requires cooperation between different organs in the body.
  • The conversion of glutamine (an amino acid) to glutamate and then to a-ketoglutarate, generates free ammonia that needs to be removed.
20
Q

What are the functions of glutamine and its metabolites?

A
  • Important source of fuel during fasting particularly in muscles, immune cells.
  • For gluconeogenesis, particularly in the kidney.
  • Produces ammonia that can acts as a buffer for protons (removed in urea)
  • Anti-inflammatory properties – in gut
21
Q

What are the sources of ammonia in the urea cycle?

A
  • Sources of ammonia:
    o Microflora in gut release ammonia when breaking down food
    o Deamination of AA (glutamine).
    o Breakdown of DNA/RNA
    o Metabolism of AA (glutamate recycling in the liver – dehydrogenase).
    o Ketogenesis/gluconeogenesis from AA releases ammonia.
22
Q

Where does the urea cycle primarily occur?

A

The liver

23
Q

What does the urea cycle require and where do they come from?

A
  • Requires two amino groups:
    o One comes from aspartate.
    o One from ammonia (carbamoyl phosphate)
24
Q

What is the key regulating enzyme in the urea cycle?

A
  • Key regulating enzyme: CP synthase
    o Requires 2 ATP molecules
    o Controlled allosterically by a metabolites of glutamate, N-acetyl glutamate, formed in an excess of glutamate so drives urea cycle.
    Glutamate + acetyl-coA -> N-acetyl glutamate + CoASH
25
Q

How can defects of urea formation occur? What might symptoms be? What are the two types of onset? What are the treatments?

A
  • Regulated by 6 enzymes, defects of any of which will cause reduction in urine formation.
  • Symptoms related to accumulation of ammonia – can be fatal in new borns.
  • Symptoms include: vomiting, nausea, neurological disorders, lethargy, coma.
  • Two types of onset:
    o neonatal
    o late-onset (post-natal; 70%)
  • Treatment – dietary management, phenylbutyrate (ammonia scavengers)
  • Thought to be undiagnosed causes of SIDS
26
Q

Summarise nitrogen metabolism.

A

Amino acids obtained from ingested protein or biosynthesis.
Amino acids can then be degraded to nitrogen (to form urea), carbon skeletons (to form ketogenic or glucogenic acids), or to form purines, pyrimidines or porphyrins.

27
Q

What are the key points of nitrogen metabolism?

A
  • Nitrogen must be kept in a balance (intake/production vs loss/metabolism)
  • Amino acids have numerous functions besides building proteins.
  • Transamination – process by which different amino acids can be created or shuttled to produce energy
  • Glucogenic vs ketogenic amino acids.
  • Reactions that generate ammonia – and its disposal (UREA CYCLE)
  • Importance of glutamine – glutamate – α-ketoglutarate

MET1 (16 decks)

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