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Biochem III > Protein and Amino acid Catabolism > Flashcards

Protein and Amino acid Catabolism Flashcards

1
Q

Why are amino acids considered glucogenic?

A

they can be converted to OAA

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2
Q

Ketogenic amino acids form what two compounds?

A

acetyl-CoA or acetoacetyl-CoA

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3
Q

Which amino acids are degraded to acetyl-CoA?

A

Leucine, Isoleucine, Tryptophan

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4
Q

What amino acids are degraded to pyruvate?

A

alanine, serine, cysteine , glycine

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5
Q

What amino acids are degraded to oxaloacetate?

A

Aspartate and asparagine

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6
Q

What amino acids are degraded to fumarate?

A

Trp, Tyr, Phe

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7
Q

What amino acids are degraded to succinyl-CoA?

A

Val, Thr, Iso, Met

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8
Q

What amino acids are degraded to a-KG?

A

Arg, His, Glu, Pro

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9
Q

During fasting or low energy state, what enzymes activity most influences amino acid metabolism?

A

mitochondrial glutamate dehydrogenase

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10
Q

What three products does glutamate dehydrogenase produce?

A

ammonium, NADH and a-KG

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11
Q

What mutant enzyme do patients with HHF6 possess?

A

they express mutant forms of GDH

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12
Q

What about these mutant forms of GDH predispose thee patients to hypoglycemia?

A

Their GDH is insensitive to inhibition by GTP

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13
Q

What does this mutant GDH produce?

A

ATP and ammonia

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14
Q

What does this excess ATP trigger?

A

insulin release

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15
Q

This aberrant activity of GDH also reduces the synthesis of what? What are the effects of this?

A

N-acetylglutamate

Decreased activity of the urea cycle

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16
Q

Where is oxalate secreted? What does oxalate have a high affinity for?

A

urine. Calcium.

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17
Q

What is the pathway for the formation of oxalate?

A

glycine –> glyoxalate –> oxalate

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18
Q

How does oxalate relate to kidney physiology?

A

calcium oxalate can precipitate and form kidney stones

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19
Q

What product does the glycine cleavage system produce?

A

N5, N10 methylene THF

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20
Q

Is the methylene cleavage system reversible?

A

Yes

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21
Q

Defects in the glycine cleavage system lead to what?

A

glycine encephalopathy

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22
Q

What is glycine encephalopathy also known as?

A

nonketotic hyperglycinemia

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23
Q

What is the function of asparaginase?

A

Asparagine to aspartate

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24
Q

What is the function of AST?

A

Aspartate to OAA

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25
Q

Propionyl-CoA Carboxylase requires what co-factor?

A

Biotin

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26
Q

Carboxylation of propionyl-CoA yields what product?

A

D-methylmalonyl-CoA

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27
Q

The conversion of L-methylmalonyl-CoA to Succinyl-CoA requries what co-factor?

A

B12

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28
Q

Where does absorption of B12 occur?

A

distal ileum

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29
Q

What is the function of transcobalamin?

A

to bind B12 once it has been absorbed

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30
Q

What is pernicious anemia?

A

lack of B12 (due to a number of reasons)

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31
Q

What reaction converts N5-methyl-THF back into THF? What enzyme catalyzes this reaction?

A

conversion of homocysteine to methionine

Methionine Synthase

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32
Q

N5, N10- methylene THF is required for the synthesis of what DNA components?

A

thymidine and purine rings

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33
Q

Name three tenets of how homocysteine may contribute to atherosclerosis?

A

oxidize LDL’s

damages cells lining arteries

interference with blood clotting system

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34
Q

BCKDH is related to what other dehydrogenase?

A

PDH

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35
Q

What are the products of the BCAA degradation?

A

branched-chain acyl-CoA’s

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36
Q

Oxidation of branched-chain acyl-CoA’s is very similar to what other degradative pathway?

A

beta-oxidation

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37
Q

What is valine coverted into?

A

propionyl-CoA

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38
Q

What is isoleucine converted into?

A

propionyl-CoA and acetyl-CoA

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39
Q

What is leucine converted into?

A

acetyl-CoA and acetoacetyl-CoA

40
Q

MSUD is characterized by defects in what complex?

A

BCKDH

41
Q

What gives MSUD its odor?

A

presence of branched chain alpha-keto acids

42
Q

What population has a high incidence of MSUD?

A

Old World Mennonite

43
Q

What enzyme is defective in tyrosinemia-II?

Tyrosinemia-II is characterized by what three conditions?

A

tyrosine aminotransferase

keratitis, photophobia, painful skin lesions

44
Q

Where do these conditions of tyrosinemia-II occur?

A

palms of hands and soles of feet

45
Q

What color does the urine of alkaptonuria patients turn when exposed to air? What compound provides for this? What enzyme is deficient in these patients?

A

black

homogentistate

Homogentistate oxidase

46
Q

Oxidation of homogentistate produces what? What will this oxidation product cause?

A

benzoquinones

pigmentation (ochronosis) of connective tissue and arthritis

47
Q

What two procedures do alkaptonuria patients often require by midlife?

A

joint and cardiac valve replacements

48
Q

What is Nitisinone?

A

drug that impedes homogenistate formation

49
Q

What enzyme is deficient in tyrosinemia-I?

A

fumarylacetoacetate hydrolase

50
Q

What two products accumulate in patients suffering from tyrosinemia-I?

A

fumarylacetoacetate and maleylacetoacetate

51
Q

In patients suffering from tyrosinemia-I, fumarylacetoacetate and maleylacetoacetate are converted to what?

A

succinylacetone

52
Q

Succinylacetone can inhibit the synthesis of what?

A

heme

53
Q

Which amino acids can be deaminated without the help of an aminotransferase?

A

serine, cysteine, histidine and theronine

54
Q

What are the substrates of carbamoyl phosphate synthetase I?

A

ATP, HCO3, ammonium

55
Q

Carbamoyl Phosphate Synthetase I requires what product as a co-factor?

A

n-acetylglutamate

56
Q

What enzyme synthesizes n-acetylglutamate? What activates this enzyme?

A

N-acetylglutamate synthetase

arginine

57
Q

What does carbamoyl phosphate condense with?

A

ornithine

58
Q

What two steps of the urea cycle take place in the mitochondria?

A

formation of carbamoyl phosphate and condensation of carbamoyl phosphate with ornithine

59
Q

What is the RLS of the urea cycle?

A

carbamoyl phosphate synthetase I

60
Q

At what point does the urea cycle leave the mitochondria? How is this achieved?

A

citrulline is exchanged for ornithine

61
Q

What product links the urea cycle to the citric acid cycle?

A

fumarate

62
Q

What is the intestinal-renal axis?

A

intestinal epithelial cells produce citrulline from glutamine

renal cells pick up citrulline and convert it to arginine

63
Q

When is the intestinal-renal axis established?

A

post-natally

64
Q

Conditions affect which two organs can affect arginine synthesis?

A

intestine or kidneys

65
Q

Which organ system can perform the entire urea cycle?

A

Liver

66
Q

WHat are the sources of the amide nitrogen in urea?

A

NH4 and aspartate

67
Q

What is the urea-TCA bicycle?

A

fumarate is generated by the urea cycle

OAA is converted to aspartate and utilized by the urea cycle

68
Q

What two drugs can be used to treat patients with defects in either carbamoyl phosphate synthetase I or ornithine transcarbamoylase?

A

phenylbutyrate and benzoate

69
Q

Ketogenic amino acids form what two products?

A

acetyl-CoA and acetoacetyl-CoA

70
Q

Under low energy charge, what enzyme most influences amino acid degradation?

A

mitochondrial glutamate dehydrogenase

71
Q

What regulates the activity of glutamate dehydrogenase?

A

cellular energy charge

72
Q

Regarding the activity of GDH, what side of the equation is NADH on?

A

alpha-KG

73
Q

Familial hyperinsulemic hypoglycemia have been found to possess a mutated version of what enzyme? What makes this enzyme defective?

A

GDH

it is resistant to inhibition by GTP

74
Q

In HHF patients, what causes insulin secretion?

A

NADH acting on beta-cells

75
Q

If now converted to serine, what else can glycine be converted to?

A

glyoxalate and oxalate

76
Q

In humans, what is the major route of glycine metabolism? What does this produce?

A

mitochondrial glycine cleavage pathway

N5N10-methylene-THF, NADH

77
Q

What enzyme degrades asparagine? What is the product?

A

asparaginase

aspartate

78
Q

Defects in the glycine cleavage pathway lead to what?

A

glycine encephalopathy

AKA

nonketotic hyperglycinemia

79
Q

What are the best sources of B12?

A

meats and shellfish

80
Q

What is MSUD characterized by regarding enzymatic defects?

A

defective branched chain alpha-ketoacid dehydrogenase complex (BCKDH)

81
Q

What enzyme is defective in alcaptonuriua?

A

homogentisate oxidase

82
Q

What enzyme does nitisinone affect the activity of? What will this impede the formation on? What disease can this help treat?

A

4-hydroxyphenylpyruvate hydroxylase

homogentisate

alcaptonuria

83
Q

What product in the urine in diagnostic of tyrosinemia-I?

A

succinylacetone

84
Q

Where is carbamoylphosphate synthetase I located?

A

mitochondria

85
Q

What does carbamoyl phosphate synthetase I require as an allosteric activatior?

A

N-acetylglutamate

86
Q

What enzyme produces N-acetylglutamate? What product activtaes the enzyme that produces N-acetylglutamate?

A

N-acetylglutamate Synthetase

Arginine

87
Q

What two enzymes of the urea cycle perform their activities in the mitochondria?

A

carbamoyl phosphate synthetase I and ornithine transcarbamoylase

88
Q

What are the nitrogen sources of urea?

A

aspartate and ammonium

89
Q

Infants born with defects in carbamoyl phosphate synthetase I or ornithine transbarbamoylase require the administration of what two drugs?

A

phenylbutyrate and benzoate

90
Q

What two amino acids are released from the muscles in the beginning of the early fast?

A

alanine and glutamine

91
Q

What is the function of tryptophan hydroxylase? What co-factor does tryptophan hydroxylase require? The activity of this enzyme leads to the formation of what?

A

add hydroxyl group to tryptophan

THBtn

serotonin

92
Q

What enzyme begins the formation of melatonin? What is the enzymatic function of this enzyme? What enzyme converts N-acetylserotonin to melatonin?

A

N-acetyltransferase

serotonin –> N-acetylserotonin

Hydroxyindole-O-methyltransferase

93
Q

What is GABA produced from? What co-factor does this reaction require?

A

glutamate

pyridoxal phosphate

94
Q

What type of bond does GST form?

A

thio-ether

95
Q

The increased degradation of glutamate to a-KG also decreases the production of what molecule involved in the urea cycle?

A

N-acetylglutamate

96
Q

What enzyme of the urea cycle develops post-natally?

A

arginpsuccinate lyase

97
Q

What is alpha-ketoisovalerate converted into?

A

ONLY glucose

Biochem III (9 decks)

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