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Nitrogen 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
transaminases participate in amino acid
synthesis AND degradation as reaction is reversiable
26
Glutamate + Pyruvate ---> | amino acid) (a-keto acid
a-keto glutarate + alanine (a-keto acid) (amino acid) note: NH3+ is with amino acids
27
All aminotransferases rely on the
pyridoxal phosphate cofactor
28
Typically, a-ketoglutarate accepts
amino groups
29
L-Glutamine acts as
a temporary storage of nitrogen | - can donate the amino group when needed for amino acid biosynthesis
30
PLP =
pyridoxal phosphate - Cofactor made from vitamin B6 (essential vitamin) - Transfers the amino group during the reaction
31
Aminotransferases are intracellular enzymes; presence in plasma indicates
cell damage
32
Liver disease followed by measuring
serum levels of ALT or AST
33
About 90% of energy needs of carnivores can be met by
amino acids immediately after a meal
34
Amino acids undergo oxidative catabolism under three circumstances:
- Leftover amino acids - Dietary amino acids - Proteins in the body are broken down
35
Leftover amino acids from normal protein turnover are
degraded
36
Dietary amino acids that exceed
body’s protein synthesis needs are degraded
37
Proteins in the body are broken down to supply
amino acids for catabolism when carbohydrates are in short supply (starvation, diabetes mellitus),
38
Pepsin cuts
protein into peptides in the stomach
39
Trypsin and chymotrypsin cut
proteins and larger peptides into smaller peptides in the small intestine
40
Aminopeptidase and carboxypeptidases A and B degrade
peptides into amino acids in the small intestine
41
Cellular proteins can also be targeted for destruction: | Used to degrade
- Misfolded proteins - Foreign proteins - Unwanted proteins Same end point as dietary proteins: - Individual amino acids
42
NH4 conversion to NO2/NO3 by bacteria to allow
uptake into cells; converted back to NH4
43
NH4 transferred to glutamate; hence
to other amino acids by transamination | - enzyme = aminotransferases
44
Plants conserve almost all of their
nitrogen
45
Many aquatic vertebrates release
ammonia to their environment - Passive diffusion from epithelial cells - Active transport via gills
46
Many terrestrial vertebrates and sharks excrete
nitrogen in the form of urea - Urea is far less toxic that ammonia - Urea has very high solubility
47
Some animals, such as birds and reptiles excrete
nitrogen as uric acid - Uric acid is rather insoluble - Excretion as paste allows to conserve water
48
Humans and great apes excrete
both urea (from amino acids) and uric acid (from purines)
49
Ammonia is Transported in the Bloodstream Safely as
Glutamine
50
Excess glutamine is processed in
intestines, kidneys and liver
51
Vigorously working muscles operate nearly anaerobically and rely on
glycolysis for energy
52
Glycolysis yields
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
What charge does glutamate have?
-ve charge
54
What charge do alanine and glutamine have?
NO charge
55
Why make glutamate, then convert it to glutamine or alanine only to convert it back in the liver?
Charged molecules don’t pass through membranes easily; hence convert to uncharged molecule to allow easy transport
56
Excess Glutamate is Metabolised in the
Mitochondria of Hepatocytes
57
The Glutamate Dehydrogenase Reaction
- 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
Ammonia is Re-captured via Synthesis of
Carbamoyl Phosphate | - This is the first nitrogen-acquiring reaction
59
Nitrogen from Carbamoyl Phosphate Enters
the Urea Cycle | - Entry of aspartate into the urea cycle is the second nitrogen-acquiring reaction
60
beta oxidation is when
fatty acids get converted into acetyl CoA (2C)
61
Carbon atoms of degraded amino acids emerge as major metabolic intermediates
``` Seven to acetyl-CoA Six to pyruvate Five to a-ketoglutarate Four to succinyl-CoA Two to fumarate Two to oxaloacetate ```
62
Primary role of carbs and fat?
To provide energy
63
Primary role of amino acids?
Building blocks for proteins
64
8 are “essential” needed in diet:
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine
65
glucogenic
Some amino acids “feed in” to gluconeogenesis and so produce glucose or glycogen, in liver.
66
ketogenic
Other amino acids “feed in” to acetoacetate or acetyl CoA.
67
ketogenic cannot result in gluconeogenesis. Why?
pyruvate dehydrogenase reaction (pyruvate to acetyl CoA) is irreversible and no NET synthesis of oxaloacetate through the citric acid cycle
68
isoleucine, tyrosine and phenylalanine
amino acids are both glucogenic and ketogenic
69
Ketone bodies facts
Small water soluble | produced by liver; used by brain in absence glucose
70
Catabolism of amino acids involves
transfer of the amino group via PLP-dependent aminotransferase to a donor such as a-ketoglutarate to yield L-glutamine
71
L-glutamine can be used to
synthesize new amino acids, or it can dispose of excess nitrogen as ammonia
72
In most mammals, toxic ammonia is
quickly recaptured into carbamoyl phosphate and passed into the urea cycle
73
Carbon skeleton of some amino acids can be used in
gluconeogenesis (glucogenic amino acids) | - Other amino acids are ketogenic (carbon skeleton forms ketone bodies)
74
Inherited Metabolic Disorders: Usually due to a single gene defect Typically result in deficiencies of key enzymes Results in abnormal synthesis or catabolism of:
- Proteins - Amino acids - Carbohydrate - Lipids
75
Inherited Metabolic Disorders: | Clinical symptoms usually
severe and typically present in infancy or childhood
76
Most Inherited Metabolic Disorders show
autosomal recessive inheritance. | - Heterozygotes are phenotypically normal
77
Some common clinical features of inherited metabolic disorders presenting in childhood:
- Acidosis - Failure to thrive - Vomiting, refusal of feeds, irritability - Central nervous system dysfunction - Hypoglycaemia - Unusual odour
78
Disorders of the urea cycle: 6 inherited disorders of the urea cycle main one is
``` ornithine transcarbamoylase (OTC) deficiency - characterised by hyperammonaemia ```
79
out of 6 inherited disorders of the urea cycle what one causes X linked disease
ornithine transcarbamoylase (OTC) deficiency
80
out of 6 inherited disorders of the urea cycle 5 of them are
autosomal recessive
81
hyperammonaemia
(elevated blood ammonia level) – highly toxic
82
Amino acid disorders:
Phenylketonuria (PKU)
83
Phenylketonuria (PKU) described as
Absence/deficiency of Phenylalanine hydroxylase (PAH) – classical PKU - Autosomal recessive disorder
84
Untreated individuals of Phenylketonuria (PKU) exhibit
signs of impaired brain development | - neurological features are evident by 6 months of age
85
Phenylketonuria (PKU) Treatable condition through
Reduced protein diet supplemented with tyrosine - Neonatal screening programme (carried out on day 5) - Positive screening test
86
Inherited metabolic disorders are individually
rare but collectively not uncommon
87
Majority of inherited metabolic disorders present clinically in
infancy/childhood, but may present in older patients | - Reduced or absent enzyme activity
88
Inherited metabolic disorders may give rise to
intoxication | - may alter energy metabolism

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