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Biochemistry 2 Final Exam > N metabolism and protein turnover > Flashcards

N metabolism and protein turnover Flashcards

1
Q

Is ammonia a neurotoxin?

A

yes

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2
Q

What percentage of the amino acids leaving the gut and liver are BCAA?

A

25%, 60%

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3
Q

What are the BCAA

A

branch-chain amino acids: leucine, valine, isoleucine

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4
Q

Where do amino acids go in the Fed state?

A

absorbed from the gut, they go to the liver for metabolism into other substances (VLDL/Chylomicrons/glycogen) before going into the blood to other cells

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5
Q

Where do amino acids go in the Fasting state?

A

glutamine, alanine and other AA from skeletal muscle go to the kidney for extraction of NH4, conversion to serine and alanine, then to the liver. glutamine also converted to alanine in the gut before going to the liver.

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6
Q

What two amino acids are Nitrogen carriers?

A

Glutamine and Alanine

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7
Q

How do the kidneys support liver gluconeogenesis during fasting?

A

The convert glutamine to alanine via transaminases. Alanine is a precursor to pyruvate, which can undergo gluconeogenesis.

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8
Q

How doe glutamine enter the TCA cycle?

A

deamidation to glutamate, deamination to a-ketoglutarate

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9
Q

What amino acid buffers hydrogen ions?

A

glutamine (as a source of ammonia)

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10
Q

What amino acid is the primary fuel for the kidneys in normal and fasting states?

A

glutamine

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11
Q

What type of energy is used by cells of the renal medulla?

A

glucose

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12
Q

What type of energy is used by cells of the renal cortex?

A

Lactate

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13
Q

What is the major fuel of the gut?

A

glutamine

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14
Q

What three things does the gut use for fuel/oxidation?

A

glutamine (major), BCAA and aspartate

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15
Q

What uses up short-chain fatty acids?

A

bacteria in the colon

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16
Q

Amino acids that produce pyruvate or Krebs cycle intermediates are called:

A

glucogenic AAs

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17
Q

Amino acids that produce acetyl CoA or acetoacetyl CoA are called:

A

ketogenic AAs

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18
Q

What two amino acids are purely ketogenic?

A

leucine and lysine

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19
Q

What five amino acids are both ketogenic and glucogenic?

A

tryptophan, phenylalanine, tyrosine (aromatics), isoleucine, threonine

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20
Q

What enzyme oxidizes the BCAA? What is the reaction type and what are the cofactors?

A

branched-chain keto-acid dehydrogenase. oxidative decarboxylation. cofactors: lipoic acid, CoA, TPP, NADH, FADH2

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21
Q

Of the 5 cofactors for the branched-chain keto-acid dehydrogenase enzyme, which is NOT a vitamin derivative?

A

lipoic acid

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22
Q

What are the two steps for BCAA degradation?

A

BCAA specific aminotransferase converts them to branched chain keto-acids which then undergo oxidative decarboxylation.

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23
Q

What is the cause for maple syrup urine disease?

A

a defective branched-chain keto-acid dehydrogenase

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24
Q

What percentage of muscle amino acid content is BCAA?

A

25%

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25
Q

What does muscle do with BCAA?

A

uses them for fuel, then converts them to alanine and glutamine to transfer N to other tissues.

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26
Q

What is the primary fuel for muscles?

A

BCAA

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27
Q

Is tyrosine an essential Amino acid? why/why not?

A

Tyrosine is NOT an essential amino acid because it can be made from phenylalanine via phenylalanine hydroxylase.

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28
Q

What enzyme converts phenylalanine to tyrosine? what is its cofactor?

A

phenylalanine hydroxylase. cofactor: tetrahydrobiopterin

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29
Q

What condition occurs when one cannot convert phenylalanine to tyrosine? What are 3 toxic by-products that can accumulate?

A

phenylketonuria. phenylpyryvate, phenyllactate, phenylacetate can accumulate

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30
Q

What is classical PKU?

A

A defect in the phenylalanine hydroxylase enzyme that can be treated by a phenylalanine-restricted diet

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31
Q

What is atypical PKU?

A

A defect in tetrahydrobiopterin reductase enzyme

32
Q

What two substances doe tyrosine eventually get catabolized to?

A

fumarate and acetoacetate

33
Q

Which substance is catabolic in nature, which is anabolic? Insulin or glucagon?

A

insulin is anabolic, glucagon in catabolic

34
Q

What differences are there between a high-carbohydrate meal versus a high-protein meal to insulin/glucagon levels?

A

a high protein diet stimulates both catabolism and anabolism, whereas a high carbohydrate diet stimulates only anabolism. Also, a the stimulation of anabolism is short-lived and drops rapidly in a high-carb meal.

35
Q

What two amino acids are the primary regulators of glucagon release?

A

arginine and leucine

36
Q

What is a negative nitrogen balance? give an example

A

N excretion higher than consumption- eg. a sick person not eating well

37
Q

What is a positive nitrogen balance? give an example

A

N excretion lower than consumption- eg. newborns using AA for growth

38
Q

What six things characterize a hypercatabolic state?

A

increased fuel metabolism and a negative nitrogen balance. degradation of skeletal muscle protein. increased synthesis of immune system components and gluconeogenesis. increased urea synthesis.

39
Q

How does insulin stimulate cholesterol uptake into cells?

A

by stimulating lipoprotein lipase

40
Q

What are the ten essential amino acids?

A

PVT TIM HALL : phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, leucine, lysine

41
Q

How is alanine synthesized?

A

transamination from pyruvate

42
Q

How is aspartate synthesized?

A

transamination of oxaloacetate

43
Q

How is asparagine synthesized?

A

amidation of aspartate

44
Q

How is glutamate synthesized?

A

glutamate dehydrogenase, a reductive amination of a-keto glutarate

45
Q

How is glutamine synthesized?

A

amidation of glutamate

46
Q

How is arginine synthesized?

A

from the urea cycle

47
Q

How is proline synthesized?

A

from glutamate

48
Q

how is serine synthesized?

A

from 3-phosphoglycerate (glycolysis)

49
Q

how is glycine synthesized?

A

from serine

50
Q

how is cystein synthesized?

A

from serine and methionine (sulfur-containing)

51
Q

how is tyrosine synthesized?

A

from phenylalanine

52
Q

What two things does and enzyme need to synthesize a reaction to form a non-essential amino acid?

A

a precursor and an amine group (from a N-donor)

53
Q

What are the three one-carbon carriers and what type of carbons do they carry?

A

biotin (CO2); tetrahydrofolate (THF) (one-carbon units in all oxidation states except CO2); S-adenosylmethionine (active methyl group donor)

54
Q

What three reactions does biotin mediate?

A

pyruvate carboxylase (in gluconeogenesis); carbonyl CoA rxns; odd-chain FA degradation

55
Q

What is SAM?

A

a ribose sugar nucleotide

56
Q

What is vitamin B9?

A

folate

57
Q

Why is folate a vitamin?

A

Because we cant synthesize the pteridine ring

58
Q

How is folic acid absorbed in the gut?

A

reductases and conjugases on the brush border deconjugate the THF from polyglutamates. THF is absorbed, then reconjugated intracellularly

59
Q

What is the most reduced form of THF and why is it unique?

A

5-methyl-FH4, it’s formation is irreversible, so it cannot form any other C oxidation states. Other forms of THF are interconvertible.

60
Q

What is the major one-carbon source, and what are three other one-carbon sources in folate derivatives?

A

serine is the major source. glycine, histidine and formate are other sources

61
Q

Which amino acid is an immediate precursor to SAM

A

methionine

62
Q

After SAM loses a carbon group, what does it become?

A

SAH

63
Q

After SAH loses Adenosine, what does it become?

A

Homocysteine

64
Q

How does homocysteine regenerate methionine? name the enzyme and two cofactors

A

homocysteine methyltransferase. requires B12 and an activated methyl from N-methylTHF.

65
Q

What two steps (name enzyme and cofactor) are required to convert homocysteine to cysteine?

A
  1. cystathionine synthase (req. pyridoxal phosphate)

2. cystathionase (req. pyridoxal phosphate)

66
Q

What is the methyl trap hypothesis?

A

inadequate B12 traps the THF methyl group from converting homocysteine to methionine. Thus no SAM is made, contributing to macrocytic anemias.

67
Q

What are five products that SAM can help produce?

A

epinephrine, creatine, methylated nucleotides, phosphatidylcholine, melatonin

68
Q

What four amino acids can be degraded to succinyl CoA?

A

valine, methionine, isoleucine, threonine

69
Q

Conversion of propionyl CoA to methylmalonyl CoA requires what vitamin cofactor?

A

biotin

70
Q

What are two reactions that require B12?

A

conversion on homocysteine to methionine; conversion on methylmalonyl CoA to Succinyl CoA

71
Q

What 2 compounds would accumulate in a B12 deficiency?

A

homocysteine (less so, as it can be converted to cysteine) and methylmalonyl CoA

72
Q

What two things in the gut are required for B12 absorption?

A

R-binders and intrinsic factor released from parietal cells

73
Q

Where is B12 absorbed in the gut?

A

the ileum

74
Q

What happens in methylmalonic aciduria?

A

defect of the methylmalonyl CoA reductase that normally converts methylmalonyl CoA to succinyl CoA. May respond to high dose of B12

75
Q

If B12 absorption is impaired, why might high doses of B12 help?

A

1% can passively diffuse through the small intestine

Biochemistry 2 Final Exam (5 decks)

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