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Flashcards in Nitrogen Metabolism Deck (98):
1

Atmospheric nitrogen

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

2

Dietary proteins

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

3

What are the two main ways of obtaining nitrogen

Air and diet

4

Is there a storage form of nitrogen in humans?

No

5

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

Because its a reactive compound

6

How does most nitrogen leave the body?

Through the urea cycle

7

What serves to clear the body of excess nitrogen

Urea cycle

8

Urea cycle

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

9

How does most nitrogen enter the body?

In the form of amino acids

10

Input of the amino acids in the amino acid pool?

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

11

Out of amino acids

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

12

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

Input and output

13

Selectively degrade damaged or short lived proteins

Proteasomes

14

What do proteasomes use to target proteins for degradation

Ubiquitin modification

15

What do proteasomes require?

ATP, energy dependent

16

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

Lysosomes

17

What do lysosomes use to break down peptide bonds

Acid hydrolases

18

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

~100g

19

Where is protein digested ?

Stomach and small intestine

20

Enzyme in the stomach that breaks down protein

Pepsin

21

Enzymes in the small intestine that breaks down protein

-pancreatic enzymes
-intestinal wall cells

22

Pancreatic enzymes

-trypsin
-chymotrypsin
-elastase
-carboxyl emptied

23

Intestinal wall cells

-aminopeptidases
-di and tripeptidases

24

What roles do HCL play?

-killing microorganism
-aiding digestion as it helps denature proteins
-converts pepsinogen to active pepsin

25

Absorption from the lumen into the enterocytes

-free AA
-di and tripeptides

26

Free AA

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

27

Absorption from the lumen into the enterocytes of di and tripeptides

By a proton-linked transport system

28

Peptides in the enterocytes

-Peptides are hydrolyzed in the cytosol to amino acids
-AA released into the portal system

29

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

Only Free AA

30

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

Liver

31

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

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

32

Branch chained amino acids

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

33

Removal of nitrogen from AA

1. Transamination
2. Oxidative deamination

34

Transamination

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

35

Oxidative deamination

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

36

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

Glutamine synthetase

37

Transport of ammonia to the liver as glutamine

-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

38

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

ALT

39

Transport of ammonia to the liver as alanine

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

40

What are names for the urea cycle

Ornithine cycle

41

Urea cycle

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

42

Where does the urea cycle primarily take place in mammals?

Liver, and to a lesser extent the kidney

43

What does the urea cycle consist of?

5 reactions
-2 mitochondrial
-3 cytsosolic

44

Is the urea cycle catabolic or anabolic?

Catabolic, ATP is used.

45

Is the synthesis of urea reversible or irreversible?

Irreversible, with a large -deltaG

46

What is the immediate precursor for both ammonia?

Glutamate

47

What is one nitrogen of the urea molecule supplied by?

Free NH3 and the other nitrogen is asparatate

48

Sources of ammonia

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

49

How much ammonia is always in the blood?

A low constant level

50

Is amonia toxisc or nah?

Super toxic

51

How is amino acid transported in the blood?

-an amino group as part of an AA
-urea

52

Free ammonia

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

53

What do kidneys do other than removing urea from circulation

Produce some free ammonia, via glutaminase

54

Where is free ammonia realized into?

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

55

Elevated levels of ammonia in the blood

Hyperammonemia

56

Hyperammonemia is a symptom of what?

Liver failure

57

Any condition that interferes with liver function can lead to what

Hyperammonemia

58

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

Ammonia intoxication which is a medical emergency

59

What can cause blurring of vision

Elevated of ammonia

60

What do the carbon skeletons of amino acids shuttle into?

Pathways we have already seen

61

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

-intermediates of the TCA cycle
-pyruvate
-acetyl coA
-acetoacetate

62

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

-Intermediates of the TCA cycle (OAA, fumarate, succinyl CoA, a-ketoglutarate
-pyruvate

63

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

-acetyl CoA
-acetoacetate

64

Glucogenic catabolism

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

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

Gluconeogensis

66

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

Net increases in glucose formation in the liver

67

Ketogenic amino acid

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

68

Precursor for acetoacetate

-acetyl coA or acetoacetyl coA

69

What are the nonessential glucogenic amino acids?

-alanine
-arginine
-asparagine
-aspartate
-cysteine
-glutamine
-glutamate
-glycine
-proline
-serine

70

Essential glucogenic amino acids

-histidine
-methionine
-threonine
-valine

71

Which nonessemtial amino acid is both glucogenic and ketogenic?

Tyrosine

72

What essential amino acids are both glucogenic and ketogenic

-isoleucine
-phenylalanine
-tryptophan

73

What essential amino acids are ketogenic?

-leucine
-lysine

74

Which nonessential amino acids are ketogenic?

None

75

Nonessential amino acids

Can be synthesized by biochemical pathways in the human cells

76

Essential amino acids

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

77

Conditionally essential amino acids

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

78

When does elevated homocysteine occur?

During methionine metabolism

79

How many disposal pathways are there for Hcy requiring vitamins?

2

80

What do elevations in plasma Hcy promote?

Oxidative damage, inflammation, and endothelial dysfunction

81

What are elevations in plasma Hcy risk factor for?

Independent risk factor for occlusive vascular disease

82

Elevated Hcy during pregnancy is associated with

Increases incidence of neural tube defects

83

Eye anomalies associated with homocystinuria

-ectopia lentis
-myopia
-glaucoma
-optic atrophy
-retinal detachment
-cataracts

84

What is homocystinuria

The disease is due to a deficiency in cystathionine synthase

85

What is albinism a defect in?

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

86

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

-tyrosine
-melanin

87

What is the most severe form of albinism

Complete albinism

88

What enzyme is deficient in complete albinism

Tyrosinase

89

What does complete albinism result in?

Complete lack of pigment

90

What enzyme deficiency causes a complete lack of pigment?

Tyrosinase

91

What are albino patients at increased risk for?

Skin cancer

92

What is a source of methyl groups in metabolism?

Methionine

93

Member of urea cycle, precursor of nitric oxide

Arginine

94

Transport of ammonia, precursor for nucleotide biosynthesis

Glutamine

95

Precursor of histamine

Histidine

96

Precursor of serotonin

Tryptophan

97

Precursor for catecholamines

Tyrosine

98

Transport of ammonia (muscle)

Alanine