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Biochem BLOCK 3 > Nitrogen Metabolism > Flashcards

Nitrogen Metabolism Flashcards

1
Q

Atmospheric nitrogen

A

Most abundant but is too inert for use in most biochemical reactions

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2
Q

Dietary proteins

A

N2 is acted upon by bacteria and plants to nitrogen containing compounds. We assimilate these as dietary compounds

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3
Q

What are the two main ways of obtaining nitrogen

A

Air and diet

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4
Q

Is there a storage form of nitrogen in humans?

A

No

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5
Q

Why must the body get rigid of any nitrogen that’s is above the needs?

A

Because its a reactive compound

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6
Q

How does most nitrogen leave the body?

A

Through the urea cycle

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7
Q

What serves to clear the body of excess nitrogen

A

Urea cycle

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8
Q

Urea cycle

A

Serves to clear the body of any excess nitrogen by also retaining any “carbon skeletons” of the nitrogen containing compounds for other uses

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9
Q

How does most nitrogen enter the body?

A

In the form of amino acids

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10
Q

Input of the amino acids in the amino acid pool?

A
  1. Amino acids from dietary protein
  2. Amino acids from protein turnover in the body
  3. Synthesis of non-essential amino acids de novo
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11
Q

Out of amino acids

A
  1. Synthesis of proteins
  2. Synthesis of other nitrogen containing compounds (nucleotides and heme)
  3. Use of the “carbon skeleton” of AA for other compounds (glucose, lipids., ketone bodies), or for energy
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12
Q

What has to be balanced for the individual to be in a steady state?

A

Input and output

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13
Q

Selectively degrade damaged or short lived proteins

A

Proteasomes

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14
Q

What do proteasomes use to target proteins for degradation

A

Ubiquitin modification

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15
Q

What do proteasomes require?

A

ATP, energy dependent

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16
Q

Nonselectively degrade intracellular proteins (autophagy( and extracellular (heterophagy)

A

Lysosomes

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17
Q

What do lysosomes use to break down peptide bonds

A

Acid hydrolases

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18
Q

How much protein do we get a day in the diet?

A

~100g

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19
Q

Where is protein digested ?

A

Stomach and small intestine

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20
Q

Enzyme in the stomach that breaks down protein

A

Pepsin

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21
Q

Enzymes in the small intestine that breaks down protein

A
  • pancreatic enzymes

- intestinal wall cells

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22
Q

Pancreatic enzymes

A
  • trypsin
  • chymotrypsin
  • elastase
  • carboxyl emptied
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23
Q

Intestinal wall cells

A
  • aminopeptidases

- di and tripeptidases

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24
Q

What roles do HCL play?

A
  • killing microorganism
  • aiding digestion as it helps denature proteins
  • converts pepsinogen to active pepsin
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25
Q

Absorption from the lumen into the enterocytes

A
  • free AA

- di and tripeptides

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26
Q

Free AA

A

Absorbed into the lumen into the enterocytes by a sodium linked secondary transport systme of the apical membrane

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27
Q

Absorption from the lumen into the enterocytes of di and tripeptides

A

By a proton-linked transport system

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28
Q

Peptides in the enterocytes

A
  • Peptides are hydrolyzed in the cytosol to amino acids

- AA released into the portal system

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29
Q

What is found in the portal vein after a meal containing protein?

A

Only Free AA

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30
Q

What organ plays a central role in absorption and transport of amino acids?

A

Liver

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31
Q

What role does liver play in absorption and transport of AA?

A

-Liver determines which amino acids will be releases into general circulation and how much

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32
Q

Branch chained amino acids

A

Are not metabolizes by the liver bu instead are sent from the liver primarily to muscle via the blood

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33
Q

Removal of nitrogen from AA

A
  1. Transamination

2. Oxidative deamination

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34
Q

Transamination

A

Transfer of the AA a-amino group to a-ketoglutarate producing an a-keto acid (derived from the original AA) and glutamate

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35
Q

Oxidative deamination

A

Results in the liberation of the amino group as free ammonia

  • these reactions occur primarily in the liver and kidney
  • also happens in the mitochondria
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36
Q

What is the enzyme that plays a role in the transport of ammonia to the liver as glutamine?

A

Glutamine synthetase

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37
Q

Transport of ammonia to the liver as glutamine

A
  • free NH3 is added to glutamate to make glutamine
  • occurs in many tissues
  • bathe form to release nitrogen into the bloodstream for transport to the liver
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38
Q

What is the enzyme responsible for the transport of ammonia to the liver as alanine?

A

ALT

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39
Q

Transport of ammonia to the liver as alanine

A
  • ALT
  • transamination of pyruvate
  • mainly in muscle cells
  • in the liver, Ala is converted to pyruvate, again by transamination (the glucose-alanine cycle)
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40
Q

What are names for the urea cycle

A

Ornithine cycle

41
Q

Urea cycle

A

-a cycle of biochemical reactions occurring in that produces urea from ammonia

42
Q

Where does the urea cycle primarily take place in mammals?

A

Liver, and to a lesser extent the kidney

43
Q

What does the urea cycle consist of?

A

5 reactions

  • 2 mitochondrial
  • 3 cytsosolic
44
Q

Is the urea cycle catabolic or anabolic?

A

Catabolic, ATP is used.

45
Q

Is the synthesis of urea reversible or irreversible?

A

Irreversible, with a large -deltaG

46
Q

What is the immediate precursor for both ammonia?

A

Glutamate

47
Q

What is one nitrogen of the urea molecule supplied by?

A

Free NH3 and the other nitrogen is asparatate

48
Q

Sources of ammonia

A
  1. Dietary amino acids
  2. From glutamine
  3. From bacterial action
  4. From amines
  5. From the catabolism of purines and pyrimidines
49
Q

How much ammonia is always in the blood?

A

A low constant level

50
Q

Is amonia toxisc or nah?

A

Super toxic

51
Q

How is amino acid transported in the blood?

A
  • an amino group as part of an AA

- urea

52
Q

Free ammonia

A

Will be removed by the liver and used for synthesis of urea

53
Q

What do kidneys do other than removing urea from circulation

A

Produce some free ammonia, via glutaminase

54
Q

Where is free ammonia realized into?

A

Urine

-contributes to the acid-base balance of the body by excreting protons (ammonium ion)

55
Q

Elevated levels of ammonia in the blood

A

Hyperammonemia

56
Q

Hyperammonemia is a symptom of what?

A

Liver failure

57
Q

Any condition that interferes with liver function can lead to what

A

Hyperammonemia

58
Q

What happens if you have elevated ammonia (above 1000micomols/l)?

A

Ammonia intoxication which is a medical emergency

59
Q

What can cause blurring of vision

A

Elevated of ammonia

60
Q

What do the carbon skeletons of amino acids shuttle into?

A

Pathways we have already seen

61
Q

What can the carbon skeletons of AA acids be converted into?

A
  • intermediates of the TCA cycle
  • pyruvate
  • acetyl coA
  • acetoacetate
62
Q

What are the glucogenic things that the carbon skeleton of AA can be converted into?

A
  • Intermediates of the TCA cycle (OAA, fumarate, succinyl CoA, a-ketoglutarate
  • pyruvate
63
Q

Ketogenic things that the carbon skeletons of the AA can be broken down into?

A
  • acetyl CoA

- acetoacetate

64
Q

Glucogenic catabolism

A

An amino acid athat can be converted into pyruvate or an intermediate of the TCA cycle. They may be used as substrates for gluconeogensis, therefore their breakdown can give rise to a net increase in glucose formation in the liver

65
Q

An amino acid that can be converted into pyruvate or an intermediate of the TCA cycle can be used for what?

A

Gluconeogensis

66
Q

What does the breakdown of glucogenic amino acids cause an increase in?

A

Net increases in glucose formation in the liver

67
Q

Ketogenic amino acid

A

Amino acids that can be converted into acetoacetate or a precursor to acetoacetate

68
Q

Precursor for acetoacetate

A

-acetyl coA or acetoacetyl coA

69
Q

What are the nonessential glucogenic amino acids?

A
  • alanine
  • arginine
  • asparagine
  • aspartate
  • cysteine
  • glutamine
  • glutamate
  • glycine
  • proline
  • serine
70
Q

Essential glucogenic amino acids

A
  • histidine
  • methionine
  • threonine
  • valine
71
Q

Which nonessemtial amino acid is both glucogenic and ketogenic?

A

Tyrosine

72
Q

What essential amino acids are both glucogenic and ketogenic

A
  • isoleucine
  • phenylalanine
  • tryptophan
73
Q

What essential amino acids are ketogenic?

A
  • leucine

- lysine

74
Q

Which nonessential amino acids are ketogenic?

A

None

75
Q

Nonessential amino acids

A

Can be synthesized by biochemical pathways in the human cells

76
Q

Essential amino acids

A

Lack enzymes necessary, so they cannot be synthesized by humans to meet the metabolic demand of the body

77
Q

Conditionally essential amino acids

A

An amino acids that would normally be considered nonessential but may become ‘essential’ to meet an increases demand

78
Q

When does elevated homocysteine occur?

A

During methionine metabolism

79
Q

How many disposal pathways are there for Hcy requiring vitamins?

A

2

80
Q

What do elevations in plasma Hcy promote?

A

Oxidative damage, inflammation, and endothelial dysfunction

81
Q

What are elevations in plasma Hcy risk factor for?

A

Independent risk factor for occlusive vascular disease

82
Q

Elevated Hcy during pregnancy is associated with

A

Increases incidence of neural tube defects

83
Q

Eye anomalies associated with homocystinuria

A
  • ectopia lentis
  • myopia
  • glaucoma
  • optic atrophy
  • retinal detachment
  • cataracts
84
Q

What is homocystinuria

A

The disease is due to a deficiency in cystathionine synthase

85
Q

What is albinism a defect in?

A

A number of enzymes that are involved in the conversion of tyrosine to melanin

86
Q

A defect in a number of enzymes that are involved in the conversion of ________ to _______ will cause albinism.

A
  • tyrosine

- melanin

87
Q

What is the most severe form of albinism

A

Complete albinism

88
Q

What enzyme is deficient in complete albinism

A

Tyrosinase

89
Q

What does complete albinism result in?

A

Complete lack of pigment

90
Q

What enzyme deficiency causes a complete lack of pigment?

A

Tyrosinase

91
Q

What are albino patients at increased risk for?

A

Skin cancer

92
Q

What is a source of methyl groups in metabolism?

A

Methionine

93
Q

Member of urea cycle, precursor of nitric oxide

A

Arginine

94
Q

Transport of ammonia, precursor for nucleotide biosynthesis

A

Glutamine

95
Q

Precursor of histamine

A

Histidine

96
Q

Precursor of serotonin

A

Tryptophan

97
Q

Precursor for catecholamines

A

Tyrosine

98
Q

Transport of ammonia (muscle)

A

Alanine

Biochem BLOCK 3 (12 decks)

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