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GI > Protein Metabolism > Flashcards

Protein Metabolism Flashcards

1
Q

What is the Haber-Bosch reaction?

A

chemical process that enables the formation of ammonia from nitrogen gas; N2 + 3H2 -> 2 NH3

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2
Q

What are the essential amino acids? Why?

A

arginine (good for growth), histidine, isoleucine, Leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine; carbon skeleton cannot be synthesized

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3
Q

Which amino acids are non-essential? Why?

A

alanine, arginine, asparagine, aspartate, cysteine (sulfur from methionine), glutamate, glutamine, glycine, proline, serine, tyrosine (from phenylalanine) carbon skeletons can be synthesized in the body

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4
Q

Why is it necessary sometimes to remove the nitrogen from amino acids?

A

utilization of amino acid carbon skeletons for energy; likewise biosynthesis of amino acids can occur by adding an amino group to the corresponding keto acid

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5
Q

What is transamination?

A

transfer of amino group from one amino acid to a keto acid in the liver to form an amino acid; pyridoxal phosphate serves as a coenzyme in these reactions, alpha ketoglutarate is often a recipient of the amino groups, forming glutamate; multiple aminotransferases exist and the amino groups are generally funneled to glutamate and aspartate

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6
Q

An increase in the presence of aminotransferases in the blood signify what?

A

sign of cellular damage; plasma levels of AST and ALT are elevated in all forms of liver disease

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7
Q

What is oxidative deamination?

A

amino group is removed from the molecule to form ammonia and the alpha keto acid; ammonia is also produced by other reactions in cells and in the gut; ammonia formed from these/other sources must be prevented from reaching high concentrations

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8
Q

Where is d-amino acid oxidase and what does it do?

A

found in cell walls of plants and microorganisms that are consumed in the diet, it is a FAD-dependent enzyme that removes amino group as ammonia, H2O2 released is degraded to H2O by catalase

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9
Q

How is glutamine synthesized?

A

glutamine synthetase catalyzes formation of glutamine from glutamate and ammonia; glutamine can go through the blood to the liver, providing non-toxic mechanism for transport of ammonia from peripheral tissues to the liver

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10
Q

What is the alanine cycle?

A

method for transport of ammonia from muscle to the liver

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11
Q

What is hyperammonenemia?

A

ammonia intoxication, elevated blood levels of ammonia, direct neurotoxic effect on CNS, may result in tremors, slurring of speech, somnolence, vomiting, cerebral edema, blurring of vision, coma and death

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12
Q

What is acquired hyperammonenemia?

A

may result from liver disease or damage, viral hepatitis, ischemia, hepatoxins or cirrhosis can result in decreased ability of the liver to metabolize ammonia to urea for excretion

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13
Q

What is hereditary hyperammonenemia?

A

can result from deficiencies in urea cycle enzymes, resulting in impairment of the ability of the liver to synthesize urea for excretion; should have protein in diet limited, administer phenylbutyrate will result in conversion to phenylacetate which will react with glutamine to form phenylacetylglutamine which is then excreted by the kidney

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14
Q

Where are the enzymes in the liver located that make urea? What donates the nitrogen that makes up the urea?

A

both mitochondrial and cytoplasmic, one nitrogen from aspartate and the other from ammonia and CO2 provides the carbon and oxygen atoms

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15
Q

What is BUN? what is it used for?

A

blood urea nitrogen levels; reduced in liver failure and elevated in renal failure, leading to uremia

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16
Q

What is the reaction for the urea cycle?

A

aspartate + NH3 + 3ATP -> Urea + fumarate + 2ADP + AMP + 2Pi + PPi + 3H2O

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17
Q

What activates carbamoyl phosphate Synthetase I?

A

N-acetylglutamate, formed from acetyl CoA and from glutamate by the action of N-acetylglutamate synthetase

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18
Q

What are the characteristics of N-acetylglutamate synthase deficiency?

A

results in a decrease of N-acetylglutamate, leading to a reduction in CPS-1 activity

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19
Q

What is carbamoyl phosphate synthase I defect?

A

referred to type of hyperammonemia

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20
Q

What results from ornithine transporter defects?

A

results in hyperornithinemia, hyperammonemia, and homocistrulinemia

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21
Q

What are the characteristics of ornithine transcarbamoylase deficiency?

A

an x-linked disorder termed type II hyperammonemia; mothers of male children with this disorder will exhibit hyperammonemia and will avoid high protein foods

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22
Q

What results from arginosuccinate synthase deficiency?

A

citrullinemia in the blood and the urine

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23
Q

What results from arginosuccinate lyase deficiency?

A

elevated levels of arginosuccinate in the blood, cerebrospinal fluid, and urine

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24
Q

What is ketogenic amino acid degradation?

A

carbon backbones metabolized to acetyl CoA or acetoacetyl CoA; can give rise to ketone bodies; Leucine and lysine are ketogenic only

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25
Q

What is glucogenic amino acid degradation?

A

carbon backbones metabolized to pyruvate or TCA cycle intermediates; can be used as substrates for gluconeogenesis; alanine, arginine, asparagine, aspartate, cysteine, glutamine, glutamate, glycine, histidine, proline, serine, methionine, threonine, and valine are glucogenic only

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26
Q

Which amino acids are both ketogenic and glucogenic?

A

tyrosine, isoleucine, phenylalanine, and tryptophan

27
Q

How can serine be broken down?

A

deaminated to pyruvate or converted to glycine which is metabolized to carbon dioxide and ammonia

28
Q

How can arginine be broken down?

A

arginase converts it to ornithine in the urea cycle

29
Q

How can phenylalanine be broken down?

A

converted to tyrosine, which then is metabolized to fumarate and oxaloacetate

30
Q

How can proline be broken down?

A

oxidized to glutamate

31
Q

How can histidine be broken down?

A

converted to glutamate

32
Q

What are the characteristics of deamidation of asparagine and glutamine?

A

amide group is removed as ammonia by the actions of glutaminase or asparaginase, forming aspartate and glutamate; rapidly growing leukemia cells cannot synthesize enough asparagine; treatment of leukemia patients wit asparaginase will lower blood asparagine levels and deprive cancer cells of a nutrient needed for rapid growth

33
Q

What are the three branched chain amino acids? How are they catalyzed?

A

isoleucine, Leucine, and valine; share an initial common pathway catalyzed by single enzymes

34
Q

How can methionine and cysteine be converted?

A

methionine is converted to methyl-donor s-adenosylmehtionine and then to homocysteine, reconversion back to methionine can occur or conversion to cysteine; methionine is metabolized to TCA cycle intermediate succinyl CoA

35
Q

What is spina bifida? How is it effected by dietary supplementation of folic acid?

A

folic acid deficiency is associated with an increased incidence of neural tube defects resulting in spina bifida

36
Q

How are derivatives of folic acid and methionine used?

A

single carbon units can be biosynthetically transferred to or removed from molecules in different oxidation states, derivatives are used for these reactions

37
Q

How are non-essential amino acids synthesized?

A

transamination of their corresponding alpha-keto acids with amino group being supplied by glutamate

38
Q

What is the precursor for proline?

A

glutamate

39
Q

How is serine synthesized?

A

from glycolytic intermediate, D3 phosphoglycerate

40
Q

How is glycine be synthesized?

A

from serine as seen for it’s degradation

41
Q

What does glutamine synthase do?

A

catalyzes biosynthesis of glutamine from glutamate and ammonia

42
Q

What does asparagine synthase do?

A

catalyzes a similar reaction from aspartate and ammonia to form asparagines

43
Q

What is hyperphenalanemia? Cause?

A

caused by an impairment of the ability to metabolize essential amino acid phenylalanine, results in PKU; type I caused by loss of phenylalanine hydrolase (most common), II and III is loss of dihydrobiopterin reductase, type IV and V is loss of dihydrobiopterin synthase

44
Q

What are the symptoms of PKU?

A

developmental and neurological defects, treatment of infants is diet restrictions, cofactor defects will also be treated with dietary tetrahydrobiopterin, need to treat pregnant mom with PKU because it can damage the fetus

45
Q

What is albinism?

A

deficiency of tyrosine hydroxylase (tyrosinase) in melanocytes, resulting in a deficiency of the ability to form melanin

46
Q

What is tyrosinemia I?

A

from fumarylacetoacetate hydrolase deficiency, associated with liver failure and death in the first year of life due to toxic effects of fumarylactoacetate

47
Q

What is tyrosinemia II?

A

due to tyrosine aminotransferase deficiency

48
Q

What is alcaptonuria?

A

homogentisate oxidase deficiency, is accompanied by secretion of homogentisate in the urine, which turns brown upon standing; oxygenation of homogentisate

49
Q

What is Parkinson’s disease?

A

reduction in neuronal cell production of dopamine due to loss of the dopamine producing cells in the brain; treat with L-dopa

50
Q

What is homocystinuria?

A

loss of cystathionine synthase causes it, homocystine is elevated in blood and urine and methionine is elevated in the blood, mental retardation, dislocation of lens, CT abnormalities; treat with pyridoxine (vitamin B6)

51
Q

What is cystathionuria?

A

caused by cystathionase deficiency, excreted in urine with no pathological complications, characterized by cysteine crystals in the kidney due to loss of membrane transport protein that permits reabsorption of cystine

52
Q

What is cystinosis?

A

lysosomal storage disease due to defective transporter for cysteine across the lysosome membrane

53
Q

What is histidinemia?

A

due to deficiency in histidinase, elevated levels of histidine occur in the blood and urine, mental retardation is common but not always present

54
Q

What enzyme defects are involved in Maple Syrup Urine disease?

A

branched chain alpha ketoacid dehydrogenase

55
Q

How is creatinine synthesized?

A

by transamidination of glycine using arginine as a nitrogen donor

56
Q

How is carnitine synthesized?

A

from protein bound lysine

57
Q

Which amino acids serve directly as neurotransmitters and which are converted to other compounds?

A

direct: glutamate and glycine; converted: GABA from glutamate, catecholamines from tyrosine and and serotonin from tryptophan, acetylcholine from choline which is from serine and methionine

58
Q

What is acetylcholine synthesized from?

A

from choline which is from serine and methionine; s-aldomet is methylating agent

59
Q

What is serotonin synthesized from and what is it used for?

A

product of tryptophan; pain perception, normal and abnormal behaviors, regulation of sleep from serotonin derivative melatonin which regulates temperature and blood pressure; hydroxytryptophan intermediate

60
Q

What is GABA used for? Synthesized from? Degraded to?

A

inhibitory neurotransmitter synthesized from glutamate and degraded to succinate; decarboxylation

61
Q

Which biologically active amines are collectively called catecholamines? Which are NT? Which are synthesized in the adrenal medulla?

A

dopamine, norepinephrine, and epinephrine; NT: dopamine and norepinephrine, Medulla: norepinephrine and epinephrine

62
Q

What is the use of NO physiologically? How is it synthesized?

A

vasodilation, neurotransmission and ability of immune system to kill tumor cells and parasites; when arginine metabolized by NO synthase to citrulline causes the release of NO

63
Q

How is histamine used in the body?

A

vasodilator secreted by mast cells in response to allergic reactions or trauma

64
Q

What are polyamines?

A

structural molecules found in association with nucleic acids, present in all cells and inhibition of their synthesis blocks cell growth; putrescine, spermidine and spermine

GI (9 decks)

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