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Foundations of Medicine > Nitrogen > Flashcards

Nitrogen Flashcards

1
Q

What are the main nitrogen containing molecules of the body?

A

Amino acids
Nucleotides

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2
Q

What is the role of dietary protein in overall nitrogen metabolism?

A

Primary role of carbs and fats - to provide energy

Primary role of amino acids - building blocks for proteins

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3
Q

How many essential and non-essential amino acids exist?

A

E 9
NE 20

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4
Q

Why do vegetarians need a variety of different plant foods to ensure adequete intake of essential amino acids?

A

Plant proteins are not as well digested and processed by the body as animal proteins, and are not as ‘complete’ as protein from meat.

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5
Q

What can cellular proteins be targeted for?

A

Destruction

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6
Q

What can cellular proteins be used for?

A
  • Misfolded proteins
  • Foreign proteins
  • Unwanted proteins
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7
Q

Eventually all proteins are

A

Turned over

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8
Q

What is a ubiquinated protein?

A

Covalently modified protein to fit into the proteosome which is effectively a protein destroying machine.

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9
Q

What is a carbon skeleton?

A

The pattern in which the carbon atoms are bonded together in a molecule

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10
Q

Where can the aminopeptidases be found?

A

Intestine - membrane bound proteins

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11
Q

How are dietary proteins enzymatically hydrolyzed?

A

Pepsin cuts proteins into peptides in the stomach

Pepsin and chymotrypsin cut proteins into smaller peptides in the small intestine

Aminopeptidase and carboxypeptidase degrade peptides in the small intestine to amino acids

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12
Q

Under which three circumstances do amino acids go under oxidative catabolism?

A

Leftover amino acids from normal protein turnover

Excess dietary amino acids

Proteins in the body are broken down (during starvation)

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13
Q

How much of a herbivores energy intake is met by amino acids?

A

Small fraction

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14
Q

What is the name given to nitrogen fixing bacteria?

A

Diazotrophs

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15
Q

What does the assimilation stage of the nitrogen cycle consist of?

A

Fixation (n2 to ammonium)
TO
Glutamate
TO
other amino acids
TO
Proteins and other amino acids

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16
Q

What is the degradation stage of the nitrogen cycle?

A

Proteins/nucleotides
TO
Other amino acids
TO
Glutamate
TO
NH4+

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17
Q

What is the effect of lightning on nitrogen gas?

A

Breaks the triple bond and makes NO(nitric oxide) or NO2 (nitrite)

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18
Q

What ways of fixing nitrogen exist?

A

Haber process, Lightning, Nitrogen fixing bacteria

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19
Q

Name two nitrogen fixing bacteria

A

Cyanobacteria and rhizobia

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20
Q

What do the nitrogen fixing bacteria require?

A

Lots of ATP, nitrogenase enzyme inhibited by oxygen - anaerobic conditions needed , cyanobacteria form heterocysts whose cell wall forms a wall to oxygen, leguminous plants contain legheomoglobin which binds to oxygen and provides an environment that nitrogenase can work.

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21
Q

What happens to ammonium once it is fixed?

A

Nitrifiction to nitrite (NO2-) to nitrate (NO3-) this is taken up by plants and microbes - then converted to ammonia via nitrile

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22
Q

What amino acid plays a key role in regards to nitrogen?

A

Glutamate

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23
Q

What is special about glutamate?

A

It is the only amino acid that can directly obtain its nitrogen from NH4 and the only one that can give up its nitrogen directly

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24
Q

What are the 4 amino acids usually found in much higher concentrations than others?

A

Alanine, glutamine, glutamate and aspartate

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25
Q

How do organisms conserve N2?

A

Transamination - The transfer of amino groups from one biological molecule to another

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26
Q

What type of reaction is transamination if the reaction is reversible?

A

Synthesis and degradation

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27
Q

What do amino transferases rely on?

A

Pyridoxal phosphate cofactor transfers the amino acid during the reaction.

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28
Q

What molecule usually accepts the amino groups?

A

Alpha ketoglutarate

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29
Q

Which molecule usually acts as a temporary storage of nitrogen?

A

L - Glutamine (possible of donating the amino acid when it is needed for biosynthesis)

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30
Q

What is pyridoxal phosphate made from?

A

Made from vitamin B6

31
Q

Why do all excess amino acids have to be catabolised?

A

There is no storage facility for protein

32
Q

How is ammonia transported in the bloodstream?

A

As glutamine

33
Q

Where is excess glutamine processed?

A

Intestines kidney and liver

34
Q

Glutamate + ammonia =

A

Glutamine

35
Q

How is alanine made?

A

Glutamate donates ammonia to pyruvate

36
Q

Why is pyruvate converted to alanine?

A

Pyruvate builds up in an anaerobically working muscle - lactic acid build up.

By forming alanine it can be transported to the liver.

37
Q

What happens to the protein that’s broken down during exercise?

A

Transported to the liver as alanine or glutamine.

Carbon skeleton is converted into glucose or oxidised as part of the citric acid cycle.

Nitrogen is excreted as ammonia and converted to urea by the urea cycle

38
Q

Why is nitrogen transported through the body as glutamine and alanine instead of glutamate?

A

Glutamate has a negative charge - does not pass readily through cell membranes

Alanine and glutamine do not bear charge

39
Q

Where is excess glutamate metabolised?

A

Mitochondria of hepatocytes

40
Q

What is the name of the process where glutamate loses its notrogen as ammoia to form alpha ketoglutarate? And what is the electron acceptor?

A

Oxidative deamination (two electron oxidation followed by hydrolysis) NAD+ and NADP+

41
Q

What is the function of Carbomyl Phosphate?

A

Recaptures the ammonia from glutamate and enters the urea cycle.

42
Q

What is the fate of ketogenic amino acids?

A

They are broken down to produce acetyl - CoA (forms ketone bodies or is oxidised in the citric acid cylce) and acetoacetylacetate.

43
Q

What are glucogenic amino acids?

A

Feed in to gluconeogenesis and can produce glucose or glycogen in the liver.

44
Q

Why can’t ketogenic amino acids produce glucose?

A

Pyruvate dehydrogenase reaction is irreversible (Pyruvate to acetyl CoA). No net increase in Oxaloacetate.

45
Q

Why can’t ketogenic amino acids produce glucose?

A

Pyruvate dehydrogenase reaction is irreversible (Pyruvate to acetyl CoA). No net increase in Oxaloacetate.

46
Q

What do all amino transferases rely on?

A

Pyridoxal phosphate cofactor

47
Q

Inherited metabolic disorders usually result in abnormal synthesis and catabolism of:

A

Amino acids
Proteins
Carbohydrates
Lipids

48
Q

When are symptoms of an inherited metabolic disorder usually most severe?

A

Infancy or childhood

49
Q

What type of inheritance pattern do IMD’s follow?

A

Autosomal recessive inheritance

50
Q

What are some of the most common clinical features of inherited metabolic disorders present in childhood?

A

Acidosis
Failure to thrive
Vomiting, refusal of feeds, vomiting
Central nervous system dysfunction
Hypoglycaemia
Unusual odor

51
Q

What happens to ingested protein that is surplus to the bodies needs? Why?

A

It is catabolised because there is no storage facility for excess proteins.

52
Q

What is the urea cycle function?

A

Converts excess ammonia into urea in the mitochondria of liver cells.

The urea forms, then enters the blood stream, is filtered by the kidneys and is ultimately excreted in the urine.

53
Q

What happens to ingested protein that is surplus to the bodies needs? Why?

A

It is catabolised because there is no storage facility for excess proteins.

54
Q

Where in the cell is the urea cycle?

A

It is split between the cytosol and the mitochondria

55
Q

How many enzymes catalyse the reaction in the liver?

A

5

56
Q

What does the concentration of the enzymes controlling the urea cycle depend on?

A

The quantity of protein in the diet

57
Q

What is the regulatory enzyme in the urea cycle?

A

CPS1 - Carbomyl Phosphate synthase

58
Q

What is the allosteric activator of CPS1? (Carbomyl phosphate synthase)

A

N Acetylglutamtae

59
Q

How many inherited disorders of the urea cycle exist?

A

6

60
Q

What may amino acids be metabolised into?

A

Other amino acids, hormones, neurotransmitters, pigments

61
Q

What do inherited gene defects in the amino acid conversion pathway result in?

A

Decreased enzyme activity
Decreased product
Increased precursors
Alternative metabolic products, potentially toxic

62
Q

What enzyme is deficient or absent in phenylketonuria?

A

Phenylalanine hydroxylase (responsible for converting phenylalanine to tyrosine)

63
Q

What type of inheritance is PKU?

A

Autosomal recessive

64
Q

Why are high levels of phenylalanine bad?

A

Toxic - can result in impaired brain development

65
Q

What is the treatment?

A

Reduced protein diet supplemented with tyrosine

66
Q

Defects of the urea cycle can lead to

A
  • Rare group of inherited metabolic disorders
  • 6 inherited disorders of the urea cycle
  • Most common is ornithine transcarbamoylase (OTC) deficiency - 1 in 40,000 UK births
  • OTC has X-linked inheritance, rest are autosomal recessive
  • Characterised by hyperammonaemia (elevated blood ammonia level) - high toxic
  • Elevated blood ammonia is a medical emergency
  • Typically presents in newborn period
67
Q

Where does the urea cycle take place?

A

Mainly in the liver

68
Q

What comprises the synthesis of urea from ammonium?

A

Comprises the synthesis
of urea from ammonium, CO2,
aspartate and bicarbonate.

69
Q

Net reaction per urea cycle

A

2 NH3 + CO2 + 3 ATP + H2O → urea + 2 ADP + 4 Pi + AMP

70
Q

What enters the urea cycle?

A

Ammonia

71
Q

What leaves the urea cycle?

A

The urea cycle removes ammonia from the blood and makes urea, which is eventually excreted as urine.

72
Q

What causes pKU

A

Amino acid phenylalanine to builds up in the body.

PKU is caused by a change in the phenylalanine hydroxylase (PAH) gene.

This gene helps create the enzyme needed to break down phenylalanine.

73
Q

How is nitrogen transported to the liver?

A

The alanine-glucose cycle

Ammonia from amino acid degradation is transaminated to form glutamate.

Foundations of Medicine (56 decks)

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