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Science for Medicine > Nitrogen > Flashcards

Nitrogen Flashcards

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Biology 101 flashcards
1
Q

What do amino acids and nucleotides contain that carbohydrates and fats don’t?

A

Nitrogen

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2
Q

Where does our nitrogen come from?

A

from our diet (we do breathe it in but we cant use it)

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3
Q

how do the plants/animals we eat get their nitrogen?

A

From nitrogen fixing bacteria – the diazotrophs

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4
Q

fixation

A

N2 in atmosphere becomes +NH4

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5
Q

ASSIMILATION

A

+NH4 to glutamate —> other amino acids —> proteins/nucleotides

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6
Q

DEGENERATION

A

proteins/nucleotides —> amino acids —> glutamate —-> +NH4 —> N2 goes back to atmosphere

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7
Q

Nitrogen is very unreactive because of

A

triple bond between the 2 nitrogen atoms

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8
Q

How do you capture all the nitrogen?

A
  • lightning with O2 (NO or NO2)
  • 200 atm pressure with iron catalyst using H2 (+NH4)
  • Nitrogen fixing bacteria (cyanobacteria in oceans)
  • root nodules in legumes contain rhizobium bacteria
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9
Q

best to worst capturing nitrigen

A
  • lightning
  • biological sea
  • industrial
  • biological farmland
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10
Q

Nitrogen fixation requires enzyme

A

nitrogenase and a LOT of energy

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11
Q

Nitrogenase is inactivated by

A

oxygen

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12
Q

O2 is abundant:

Nitrogen fixing bacteria live

A

anaerobically.

Some uncouple mitochondria – increases electron flow and “burns” off O2 in cell

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13
Q

O2 is abundant:

Some cyanobacteria form

A

heterocysts whose “cell wall” prevents O2 entry

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14
Q

Leguminous plants produce

A

leghemoglobin which binds to O2 and keeps the concentration low enough to allow nitrogenase to work
- Example of the symbiotic relationship between the bacteria and the plant

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15
Q

NO3- =

A

nitrate

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16
Q

NO2- =

A

nitrification nitrate

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17
Q

Usable form of nitrogen; taken up by plants and microbes

A

NO3- and turned into NO2-

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18
Q

Flow of N from NH4+ to other biomolecules occurs through

A

glutamate.

  • a-ketoglutarate (citric acid cycle intermediate)
  • Glutamate (coded amino acid)
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19
Q

Glutamate is the only amino acid that can

A

obtain its nitrogen directly from NH4 AND the only one that can give up its nitrogen directly.

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20
Q

Central role of glutamate

A

4 amino acids found in much higher concs in cells compared to other a/a
Alanine, glutamine, glutamate and aspartate

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21
Q

Glutamate and aspartate are

A

excitatory neurotransmitters

- Glu also important in taste (monosodium glutamate

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22
Q

Glu has central role in

A

a/a breakdown

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23
Q

Nitrogen assimilation:
Most organisms can’t fix N2, so they conserve what N2 they do have
How?

A

By transferring amino groups between different molecules – transamination

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24
Q

Transamination – general principles

A

Note: no loss or gain of nitrogen (robbing Peter to pay Paul)
Readily reversible
One of the 2 substrate pairs is often glutamate

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25
Q

transaminases participate in amino acid

A

synthesis AND degradation as reaction is reversiable

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26
Q

Glutamate + Pyruvate —>

amino acid) (a-keto acid

A

a-keto glutarate + alanine
(a-keto acid) (amino acid)

note: NH3+ is with amino acids

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27
Q

All aminotransferases rely on the

A

pyridoxal phosphate cofactor

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28
Q

Typically, a-ketoglutarate accepts

A

amino groups

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29
Q

L-Glutamine acts as

A

a temporary storage of nitrogen

- can donate the amino group when needed for amino acid biosynthesis

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30
Q

PLP =

A

pyridoxal phosphate

  • Cofactor made from vitamin B6 (essential vitamin)
  • Transfers the amino group during the reaction
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31
Q

Aminotransferases are intracellular enzymes; presence in plasma indicates

A

cell damage

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32
Q

Liver disease followed by measuring

A

serum levels of ALT or AST

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33
Q

About 90% of energy needs of carnivores can be met by

A

amino acids immediately after a meal

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34
Q

Amino acids undergo oxidative catabolism under three circumstances:

A
  • Leftover amino acids
  • Dietary amino acids
  • Proteins in the body are broken down
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35
Q

Leftover amino acids from normal protein turnover are

A

degraded

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36
Q

Dietary amino acids that exceed

A

body’s protein synthesis needs are degraded

37
Q

Proteins in the body are broken down to supply

A

amino acids for catabolism when carbohydrates are in short supply (starvation, diabetes mellitus),

38
Q

Pepsin cuts

A

protein into peptides in the stomach

39
Q

Trypsin and chymotrypsin cut

A

proteins and larger peptides into smaller peptides in the small intestine

40
Q

Aminopeptidase and carboxypeptidases A and B degrade

A

peptides into amino acids in the small intestine

41
Q

Cellular proteins can also be targeted for destruction:

Used to degrade

A
  • Misfolded proteins
  • Foreign proteins
  • Unwanted proteins

Same end point as dietary proteins:
- Individual amino acids

42
Q

NH4 conversion to NO2/NO3 by bacteria to allow

A

uptake into cells; converted back to NH4

43
Q

NH4 transferred to glutamate; hence

A

to other amino acids by transamination

- enzyme = aminotransferases

44
Q

Plants conserve almost all of their

A

nitrogen

45
Q

Many aquatic vertebrates release

A

ammonia to their environment

  • Passive diffusion from epithelial cells
  • Active transport via gills
46
Q

Many terrestrial vertebrates and sharks excrete

A

nitrogen in the form of urea

  • Urea is far less toxic that ammonia
  • Urea has very high solubility
47
Q

Some animals, such as birds and reptiles excrete

A

nitrogen as uric acid

  • Uric acid is rather insoluble
  • Excretion as paste allows to conserve water
48
Q

Humans and great apes excrete

A

both urea (from amino acids) and uric acid (from purines)

49
Q

Ammonia is Transported in the Bloodstream Safely as

A

Glutamine

50
Q

Excess glutamine is processed in

A

intestines, kidneys and liver

51
Q

Vigorously working muscles operate nearly anaerobically and rely on

A

glycolysis for energy

52
Q

Glycolysis yields

A

pyruvate that muscles cannot metabolize aerobically; if not eliminated lactic acid will build up.

  • This pyruvate can be converted to alanine for transport into liver
  • Carbon skeleton —> pyruvate
  • Nitrogen excreted as ammonia (ammonium ion) and converted to urea by the urea cycle
53
Q

What charge does glutamate have?

A

-ve charge

54
Q

What charge do alanine and glutamine have?

A

NO charge

55
Q

Why make glutamate, then convert it to glutamine or alanine only to convert it back in the liver?

A

Charged molecules don’t pass through membranes easily; hence convert to uncharged molecule to allow easy transport

56
Q

Excess Glutamate is Metabolised in the

A

Mitochondria of Hepatocytes

57
Q

The Glutamate Dehydrogenase Reaction

A
  • Two-electron oxidation of glutamate followed by hydrolysis
  • Net process is oxidative deamination of glutamate
  • mitochondrial matrix
  • Can use either NAD+ or NADP+ as electron acceptor
58
Q

Ammonia is Re-captured via Synthesis of

A

Carbamoyl Phosphate

- This is the first nitrogen-acquiring reaction

59
Q

Nitrogen from Carbamoyl Phosphate Enters

A

the Urea Cycle

- Entry of aspartate into the urea cycle is the second nitrogen-acquiring reaction

60
Q

beta oxidation is when

A

fatty acids get converted into acetyl CoA (2C)

61
Q

Carbon atoms of degraded amino acids emerge as major metabolic intermediates

A 
Seven to acetyl-CoA
Six to pyruvate
Five to a-ketoglutarate
Four to succinyl-CoA
Two to fumarate
Two to oxaloacetate
62
Q

Primary role of carbs and fat?

A

To provide energy

63
Q

Primary role of amino acids?

A

Building blocks for proteins

64
Q

8 are “essential” needed in diet:

A

Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine

65
Q

glucogenic

A

Some amino acids “feed in” to gluconeogenesis and so produce glucose or glycogen, in liver.

66
Q

ketogenic

A

Other amino acids “feed in” to acetoacetate or acetyl CoA.

67
Q

ketogenic cannot result in gluconeogenesis. Why?

A

pyruvate dehydrogenase reaction (pyruvate to acetyl CoA) is irreversible and no NET synthesis of oxaloacetate through the citric acid cycle

68
Q

isoleucine, tyrosine and phenylalanine

A

amino acids are both glucogenic and ketogenic

69
Q

Ketone bodies facts

A

Small water soluble

produced by liver; used by brain in absence glucose

70
Q

Catabolism of amino acids involves

A

transfer of the amino group via PLP-dependent aminotransferase to a donor such as a-ketoglutarate to yield L-glutamine

71
Q

L-glutamine can be used to

A

synthesize new amino acids, or it can dispose of excess nitrogen as ammonia

72
Q

In most mammals, toxic ammonia is

A

quickly recaptured into carbamoyl phosphate and passed into the urea cycle

73
Q

Carbon skeleton of some amino acids can be used in

A

gluconeogenesis (glucogenic amino acids)

- Other amino acids are ketogenic (carbon skeleton forms ketone bodies)

74
Q

Inherited Metabolic Disorders:
Usually due to a single gene defect
Typically result in deficiencies of key enzymes
Results in abnormal synthesis or catabolism of:

A
  • Proteins
  • Amino acids
  • Carbohydrate
  • Lipids
75
Q

Inherited Metabolic Disorders:

Clinical symptoms usually

A

severe and typically present in infancy or childhood

76
Q

Most Inherited Metabolic Disorders show

A

autosomal recessive inheritance.

- Heterozygotes are phenotypically normal

77
Q

Some common clinical features of inherited metabolic disorders presenting in childhood:

A
  • Acidosis
  • Failure to thrive
  • Vomiting, refusal of feeds, irritability
  • Central nervous system dysfunction
  • Hypoglycaemia
  • Unusual odour
78
Q

Disorders of the urea cycle:
6 inherited disorders of the urea cycle
main one is

A 
ornithine transcarbamoylase (OTC) deficiency
- characterised by hyperammonaemia
79
Q

out of 6 inherited disorders of the urea cycle what one causes X linked disease

A

ornithine transcarbamoylase (OTC) deficiency

80
Q

out of 6 inherited disorders of the urea cycle 5 of them are

A

autosomal recessive

81
Q

hyperammonaemia

A

(elevated blood ammonia level) – highly toxic

82
Q

Amino acid disorders:

A

Phenylketonuria (PKU)

83
Q

Phenylketonuria (PKU) described as

A

Absence/deficiency of Phenylalanine hydroxylase (PAH) – classical PKU
- Autosomal recessive disorder

84
Q

Untreated individuals of Phenylketonuria (PKU) exhibit

A

signs of impaired brain development

- neurological features are evident by 6 months of age

85
Q

Phenylketonuria (PKU) Treatable condition through

A

Reduced protein diet supplemented with tyrosine

  • Neonatal screening programme (carried out on day 5)
  • Positive screening test
86
Q

Inherited metabolic disorders are individually

A

rare but collectively not uncommon

87
Q

Majority of inherited metabolic disorders present clinically in

A

infancy/childhood, but may present in older patients

- Reduced or absent enzyme activity

88
Q

Inherited metabolic disorders may give rise to

A

intoxication

- may alter energy metabolism

Science for Medicine (16 decks)

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