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Biochem Exam 2 > Nitrogen Metabolism > Flashcards

Nitrogen Metabolism Flashcards

1
Q

Use of amino acids carbon skeletons requires excretion of ______

A

amino nitrogen

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2
Q

What are the essential amino acids?

A

lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, methionine, histidine, arginine (there’s 10)

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3
Q

What is a good mnemonic to remember the essential amino acids?

A

PVT. TIM HALL

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4
Q

How does the body made non-essential amino acids?

A

carbons from glucose and nitrogen from glutamate (glutamate is a universal nitrogen donor)

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5
Q

If the body gets insufficient levels of an amino acid what will happen?

A

the body will break down muscle to get the amino acid it needs

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6
Q

Some plant protein sources are low in which amino acids?

A

methionine and lysine

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7
Q

Plants do not contain which essential vitamins?

A

B12 and vitamin D

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8
Q

most amino acids are glucogenic, what does that mean? Which amino acids are NOT glucogenic?

A

they can be used to make glucose (except lysine and leucine)

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9
Q

What are the main precursors to gluconeogenesis?

A

lactate, glycerol, alanine (glutamine in kidney)

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10
Q

lysine and leucine can be metabolized to generate what?

A

ketone bodies (they are ketogenic)

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11
Q

In addition to lysine and leucine which other amino acids can be broken down to ketone bodies?

A

isoleucine, threonine, tryptophan
(phenylalanine and tyrosine?)

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12
Q

conversion of amino acids to carbohydrate results in production of ____ which needs to be converted to _____

A

ammonium, urea

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13
Q

In order for proteins to break down what sequence of events must happen?

A

pepsin + HCL in stomach,
many proteases: pancreas

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14
Q

What kinds of peptides can be digested?

A

amino acids (single)
or di and tri amino acids which get broken down by di/tri peptases

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15
Q

what is an exoprotease?

A

cut off the amino or carboxy terminal amino acid off

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16
Q

what are endoproteases?

A

cut amino acid at specific site

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17
Q

What amino acids does trypsin cut?

A

arg, lys (positve)

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18
Q

what is a zymogen?

A

inactive form that must be activated in order to begin to work (this is important for keeping the enzymes from digesting our own tissues)

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19
Q

What activates trypsinogen to become trypsin?

A

enteropeptidase

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20
Q

What does pepsin look for to cut?

A

Phe, Tyr (both aromatic)
Glu, Asp (negative)

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21
Q

What activates pepsinogen to become pepsin?

A

H

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22
Q

review the chart on slide 250

A

pepsin vs trypsin

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23
Q

How are amino acids transported across the cell membranes?

A

Na linked carriers

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24
Q

uric acid is a biproduct of ____ metabolism

A

purine

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25
Q

are transfers of amino acids reversible?

A

yes

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26
Q

what is the most common amino donor and amino acceptor?

A

donor: glutamate
acceptor: alpha-ketoglutarate

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27
Q

What is the key cofactor for aminotransferase reactions? what is it derived from?

A

PLP pyridoxal phosphate
needs B6 (this vitamin is extremely important for neurotransmitters)

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28
Q

What is needed to git rid of the amino group completely?

A

glutamate dehydrogenase (takes amine group off to make ammonium which needs to be excreted as urea)

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29
Q

urea has two nitrogen’s, where do they come from?

A

ammonium and aspartate

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30
Q

what are the precursors of the urea cycle?

A

bicarbonate and free ammonium (they combine to make carbamoyl phosphate)

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31
Q

what are the products of the urea cycle?

A

urea

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32
Q

where does the urea cycle happen?

A

mitochondria in liver

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33
Q

What amino acids are involved in the urea cycle?

A

aspartate, arginine

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34
Q

What are the general steps of the urea cycle?

A

–bicarbonate joins with free ammonium
–ornithine becomes citrulline leaves mito
–hooks up with aspartate
–loses fumarate becomes arginine

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35
Q

what happens when the liver is damaged?

A

ammonium can accumulate in the blood causing a coma or death

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36
Q

what happens when there is an excess of glutamate?

A

glutamate combines with acetyl coa to make n-acetyl-glutamate (hereditary diseases that cause this step not to happen can cause ammonia accumulation)

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37
Q

After 12 hrs of fasting, glycogen is depleted, so muscle will break down protein and release free ______; this gets converted to ____ and ammonium in liver; ammonium -> urea!

A

alanine, pyruvate,

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38
Q

what are the two key amino acids in nucleotide biosynthesis?

A

serine and glycine

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39
Q

serine can be synthesized from _____

A

glucose (they are not essential so they can be

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40
Q

serine donates carbon to ____ in metabolism of glycine

A

folate (FH4)

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41
Q

Breakdown of glycine can yield ___ and ____

A

carbon and folate

42
Q

____ and ____ are key sources of carbon for folate

A

serine and glycine

43
Q

__________ is critical for nucleotide synthesis

A

folate

44
Q

Folate can be used to make which nucleotides?

A

purine nucleotides and deoxythymidine (dTMP)

45
Q

Folate can also transfer a carbon (in the form of a methyl group) to ___ which can transfer carbon to other pathways

A

B12

46
Q

Folate from our diet is reduced to ____ to be ‘activated’ in the body’

A

FH4

47
Q

What enzyme is needed to activate folate?

A

dihydrofolate reductase

48
Q

FH4 can carry a carbon in a variety of oxidation states, in the formyl phase it can generate _____

A

purines (A and G)

49
Q

FH4 can carry a carbon in a variety of oxidation states, in the methylene phase it can generate _____

A

pyrimidine (T)

50
Q

FH4 can carry a carbon in a variety of oxidation states, in the methyl phase it can generate _____

A

B12

51
Q

The only way folate can get rid f the methyl group is _____. Is this the same for the formyl and methylenes?

A

b12
no, formyl and meth can go back and fourth depending on what is needed. once methylene goes to methyl it CANNOT go back

52
Q

A B12 deficiency can lead to a ____ deficiency, why?

A

because there in the other forms the FH4 can be recycled but sine the methyl cant go back there becomes a methyl trap, methionine synthetase levels decrease. This causes more folate to be trapped as the 5-methyl derivative

53
Q

Folate deficiency leads to________

A

megaloblastic anemia

54
Q

why does folate deficiency cause megaloblastic anemia?

A

because folate is key in nucleotide synthesis and without it DNA cant replicate properly for blood cell maturation (in early pregnancy folate definicy can cause defects like spina bifida)

55
Q

what does megaloblastic anemia cause?

A

failure of blood cell precursors to make their final division (decreased mature red blood cells and instead megaloblasts circulate in blood)

56
Q

What can a B12 deficiency cause?

A

megaloblastic anemia (because without b12 folare is trapped in methyl form)

57
Q

What causes pernicious anemia?

A

destruction of parietal cells causes deficiency due to poor absorption of things such as b12)

58
Q

Why is megaloblastic anemia related to decreased nucleotide synthesis?

A

all dividing cells rely on nucleotide biosynthesis to make the nucleotides that need to replicate, they need folate and B12 to do this……because humans synthesize almost all of their nucleotides, we no not really use the ones from the food we eat

59
Q

What amino acids are needed to make pyrimidines? (U,C,G)

A

glutamine and aspartate, carbon from FH4

60
Q

Purines (A and G) are formed from

A

glutamine, glycine, aspartate and and carbon from FH4 (remember FH4 gets its carbon from serine and glycine)

61
Q

What enzymes are a target for cancer trugs to control the production of nucleotides in cancer cells?

A

dihydrofolate reductase and thymidine synthase (in essence these cancer drugs are giving you the same symptoms/situation as a folate deficiency)

62
Q

deficiency’s in folate and b12 are linked to which oral health issues?

A

glossitis (tongue inflammation)
angular cheilitis (inf of corner of mouth)
recurrent aphthous stomatitis (mouth ulcer)

(because folate and b12 are important for cell division in all cells)

63
Q

B12 deficency can also cause accumulation of _______ which can cause heart disease, thromboembolism)

A

homocysteine

64
Q

B12 deficiency can cause accumulation of _____ which is linked to demyelination of axons, neurological disease)

A

methylmalonate

65
Q

absorption of b12 requires _____ secreted in the stomach

A

intrinsic factor

66
Q

how can b12 absorption be enhanced if there is issues with pernicious anemia?

A

B12 injections, sublingual B12 (because these put b12 right to blood stream)

67
Q

B12 transfers methyl group to generate ____ a key methyl group donor

A

SAM

68
Q

Norepinephrine and SAM makes

A

epinephrine

69
Q

acetylserotinin + sam =

A

melatonin

70
Q

nucleotides + SAM =

A

methylated nucleotides (important for gene expression)

71
Q

guanidinoacetate + SAM =

A

creatine

72
Q

serotonin and melatonin derive from _____

A

tryptophan

73
Q

catecholamines derive from

A

phenylalanine/tyrosine
(remember SAM methylates norep-ep)

74
Q

histamine derives from

A

histidine

75
Q

Nitric oxide derives from

A

arginine

76
Q

Glutamate and GABA derive from

A

glutamine or alpha-ketoglutarate

77
Q

ammine groups can be transferred from BCAA’s to be combine _____ to make _____

A

pyruvate, alanine ( in liver the reverse of this can happen)

78
Q

What are branched chain amino acids (BCAA)?

A

deaminated and metabolized in muscle and brain to drive ATP production

79
Q

first step on BC amino acid metabolism:

A

transamination (remove the amino group)

80
Q

what are the branched amino acids?

A

leucine, isoleucine, valine

81
Q

second step of BC amino acid metabolism:

A

decarboxylation

82
Q

what enzyme is important for BCAA metabolism?

A

a-ketoacid dehydrogenase

83
Q

What occurs during catecholamine biosynthesis?

A

Conversion of phenylalanine to tyrosine
depends on phenylalanine hydroxylase

84
Q

What is a disease that can be caused by decrease in a-ketoacid dehydrogenase?

A

maple syrup urine, accumulation of the BCAA in urine causes sweet smell

85
Q

How is maple syrup urine treated?

A

low protein diet, limiting levels of BCAA

86
Q

what causes classical phenylketonuria (PKU)?

A

Phenylalanine hydroxylase is defective; phenylalanine (Phe) cannot be
converted to tyrosine. Phe is converted to other products such as
phenylpyruvate and phenylacetate, which can accumulate to toxic
levels

87
Q

how is PKU treated?

A

Treatment: Diet must restrict levels of phenylalanine, with supplementation of tyrosine. Aspartame (Nutrasweet) contains phenylalanine equivalents and must be avoided.

88
Q

what occurs with alkaptonuria?

A

Defect in homogentisate dioxygenase (in Tyr degradation pathway); leads to accumulation of homogentisate in tissues, bone, urine.
* Homogentisate turns dark brown/black upon oxidation (to “alkapton”, oxidation product). Urine turns black after exposure to air

89
Q

what is homocysteine metabolism?

A

It is metabolized to cystathionine (by
cystathionine synthase) This metabolism depends on PLP (pyridoxal phosphate), which is derived from dietary vitamin B6.

90
Q

Where does alkapton accumulate? What can this cause?

A

–Alkapton can also accumulate in
cartilage, bone, sclera. TEETH
–Can precipitate, leading to arthritis,
also damage to heart valves and
kidneys; sialolithiasis (stones in
salivary gland) can also occur

91
Q

What causes homocystinuria?

A

Defect in cystathionine synthase, leads to accumulation of homocystine (oxidized homocysteine) in blood and urine.

92
Q

Elevated purine degradation can lead to ____

A

gout

93
Q

What symptoms are there of homocystinuria?

A

HCU results in a range of symptoms, including risk of cardiovascular
disease and thromboembolism.
–sunken chest
–lens dislocation

94
Q

How is homocystinuria treated?

A

high dose of vit B6
also increasing methionine, B12 and folic acid can help metabolize HC through increasing activity of methionine synthase pathway

95
Q

The major purine degradation product
is _____

A

uric acid

96
Q

What is a drug that can help with gout?

A

allopurinol (inhibits xanthine oxidase)

97
Q

What is a hypercatabolic state? What causes this?

A

increased fuel utilization and negative nitrogen balance (nitrogen excreted is greater than the amount consumed). HS occurs following trauma, surgery, or critical illness

98
Q

HS is associated with elevated levels of _____

A

cortisol; cortisol release
stimulates glucose / fatty acid metabol

99
Q

Why does hypercatabolic state maintain normal tissue function?

A

The resulting mobilization of protein, lipid and carbohydrate serves to maintain normal tissue function in the presence of limited dietary intake, as well as to support the requirements of the immune response and wound healing
(after surgery or major illness you may lose appetite, body mobilizes more fuels)

100
Q

what cells get the top priority during HS?

A

immune cells

Biochem Exam 2 (6 decks)

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