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BMSC 230 > Chapter 30 - AA Degradation and the Urea Cycle > Flashcards

Chapter 30 - AA Degradation and the Urea Cycle Flashcards

1
Q

T/F: There is no protein whose sole job is to act as a storage depot for amino acids

A

True

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2
Q

amino acid input in animals

A
  • protein turnover
  • dietary proteins
  • amino acid biosynthesis
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3
Q

amino acid utilization in animals

A
  • synthesis of proteins
  • synthesis of nitrogenous molecules
  • degradation of amino acids carbon skeleton (acetyl coA)
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4
Q

half-life of regulatory proteins

A

minutes to hours

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5
Q

half-life of collagen

A

weeks/months/years

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6
Q

2 major protein degradation pathways

A
  • ubiquitin-proteasome pathway

- chemical signals

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7
Q

average dietary intake of protein

A

70-100g/day

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8
Q

Generally, proteins are too large to be absorbed intact so….

A

they are digested into amino acids and di- and tri- peptides

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9
Q

proteolysis

A

the hydrolytic cleavage of proteins by proteases; occurs in stomach and small intestine

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10
Q

endopeptidases

A
  • trypsin
  • chemotrypsin
  • elastase
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11
Q

exopeptidases

A
  • carboxypeptidases A + B

- amino peptidases

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12
Q

acidic environments…

A

denature proteins and enhance proteolysis

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13
Q

gastroesophageal reflux disease (GERD)

A

a condition where the stomach acid leaks back to the esophagus
-The K+/H+ pump in the
membrane of specialized stomach cells pumps protons into the stomach in exchange for K+ at the expense of ATP hydrolysis
-generates acidic environment and releases heat

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14
Q

medications for GERD

A
  • antacids
  • histamine H2 receptor clockers
  • proton pump inhibitors
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15
Q

zymogens

A

inactive proteolytic enzymes so that they don’t breakdown proteins in the cells where they are made and stored

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16
Q

how are zymogens activated?

A

by proteolysis, which allows for proper folding of the enzyme

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17
Q

pepsin

A

preferentially cleaves pepDde bonds between hydrophobic amino acids and aromaDc amino acids

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18
Q

trypsin

A

cleaves peptide bonds following Arg or Lys residues

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19
Q

chymotrypsin

A

preferentially cleaves peptide bonds after an aromatic amino acid

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20
Q

elastase

A

cuts after amino acids with smaller, hydrophobic side chains such as Glycogen, Ala

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21
Q

T/F: proteases self-inactivate

A

TRUE

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22
Q

Excess amino acids are not secreted or stored, so have to be……

A

metabolized to other molecules that can be excreted or used for other purposes

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23
Q

transamination reaction

A

reversible reaction that transfers amino group to a-KG

-catalyzed by aminotransferase

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24
Q

obligatory step of transamination

A

degradation of amino acids (except Lys and Thr and Pro)

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25
Q

aminotransferases/transaminases required the coenzyme _________________.

A

pyridoxal phosphate; derived from pyridoxine (vit B6)

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26
Q

glutamate + pyruvate –»

A

alanine + a-KG

-catalyzed by alanine transaminase

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27
Q

glutamate + oxaloacetate –»

A

aspartate + a-KG

-catalyzed by AST

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28
Q

fate of glutamate in liver

A

transported to mitochondria and undergoes oxidative deamination to release ammonia

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29
Q

ratio of ammonia vs ammonium depends on?

A

pH

-pH 7.4 = 98.3% NH4+ (ammonium)

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30
Q

oxidative deamination of glutamate

A
  • reversible rxn that removes amino group from Glu as NH4+
  • catalyzed by glutamate dehydrogenase
  • in mitochondrial matrix
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31
Q

coenzymes of glutamate dehydrogenase

A

NAD+ and NADP+

32
Q

positive allosteric modulator of glutamate dehydrogenase

A

ADP

33
Q

negative allosteric modulator of glutamate dehydrogenase

A

GTP

34
Q

high concentration of ______ is toxic

A

NH4+

35
Q

NH4+ is converted to what in the liver?

A

urea

36
Q

How does Ammonia that is Produced in Non-Liver Tissues get to the Liver so it can be Converted to Urea? (in most tissues)

A
  • NH4+ reacts w/ glutamate to form glutamine (catalyzed by glutamine synthetase)
  • glutamine is a nontoxic storage and transport for of NH4+
  • it is transported via blood to liver
  • NH4+ released from Gln by cleavage by glutaminase
37
Q

How does Ammonia that is Produced in Non-Liver Tissues get to the Liver so it can be Converted to Urea? (in muscle)

A
  • glutamate transfers amino group to pyruvate to form alanine
  • alanine leaves muscle into blood to liver
  • undergoes transamination to release amino group as ammonium
  • ALSO, glutamine can be formed from glutamate and released from muscle to liver
38
Q

the urea cycle

A

cyclical pathways whereby excess NH4+ is converted to urea

-occurs in liver

39
Q

precursors of urea

A

NH4+, CO2, and aspartate

40
Q

where does the urea produced go?

A

it is secreted into the blood, filtered by kidney, then excreted in urine.

41
Q

carbamoyl phosphate synthesis

A
  • rate limiting step, regulated
  • requires 2 ATP
  • catalyzed by carmaboyl phosphate synthetase I (CPSI) (requires N-acetylglutamate as allosteric activator)
42
Q

how is N-acetylglutamate formed?

A

from acetylCoA and Glu by N-acetylGlu synthase (stimulated by arginine)

43
Q

some of the glutamate is used to form _____ which provides the second ammonium group

A

aspartate

44
Q

advantages of clustering

A
  • rapid rxn rates
  • intermediates remain in complex
  • conc of intermediates is high
  • intermediates do not undergo side rxns
45
Q

___ and ______ link the urea cycle and the citric acid cycle

A

Asp. and fumarate

46
Q

urea cycle overall rxn

A

Asp + NH4+ + HCO3-, + 3ATP –> urea, fumarate, 2ADP + AMP + 2Pi + PPi

47
Q

ammoniotelic organisms

A

release ammonia directly (usually aquatic organisms)

48
Q

uricotelic organisms

A

secrete nitrogen as the purine uric acid, require little water
-generally used by organisms that can’t afford to lose water: reptiles, birds

49
Q

sources of free NH4+

A
  • dietary and body protein
  • kidneys
  • amines (norepinephrine)
  • purine and pyrimidine catabolism
50
Q

major source of ammonia

A

amino acids from diet or protein turnover via transdeamination in liver

51
Q

While ammonia is constantly being produced, its level in the blood are kept low by what mechanisms?

A
  • formation of urea
  • formation of glutamate in muscle by glutamate dehydrogenase
  • formation of glutamine in most tissues by glutamine synthetase
52
Q

hyperammonemia

A
  • ammonia is particularly toxic to CNS

- brain tries to reduce levels by synthesizing glutamine from glutamate

53
Q

increased levels of glutamine

A

Glutamine is an osmolyte in astrocytes, which causes an uptake of water and thus brain swelling

54
Q

decreased levels of glutamate

A

Glutamate is itself a neurotransmitter, but also a substrate for the synthesis of a second neurotransmitter, GABA (gamma aminobutyrate); so neurotransmitter function is affected

55
Q

symptoms of hyperammonemia

A

tremors, slurring of speech, blurred vision, cerebral edema, coma

56
Q

Causes of hyperammonemia?

A
  • acquired: liver damage

- congenital: genetic

57
Q

acquired hyperammonemia

A
  • liver damage from viral hepatitis, hepatotoxins

- when liver becomes cirrhotic

58
Q

congenital hyperammonemia

A

-defects in genes coding for all 5 urea cycle enzymes

59
Q

treatments for hyperammonemia

A
  • early treatment regimen was to inhibit protein intake and increase caloric intake to reduce amino acid catabolism
  • more recent, compounds administered that bind amino acids, forming compounds excreted in urine
60
Q

compounds that are administered to bind to amino acid to treat hyperammonemia target glutamine. why?

A
  • not an essential AA
  • main carrier of ammonium from peripheral tissues
  • contain 2 amino groups
61
Q

glucogenic

A

amino acids that are catabolized to pyruvate or an intermediate of the TCA cycle, since they can be used for glucose synthesis via gluconeogenesis

62
Q

ketogenic

A

amino acids that are catabolized to acetyl CoA or acetoacetate; can lead to formation of FA, ketone bodies, or their precursors

63
Q

Most ketogenic amino acids are also glycogenic except for…

A

lysine and leucine

64
Q

T/F: gluconeogenesis is a simple reversal of glucose synthesis

A

FALSE

65
Q

catabolic pathways for Top, Ala, Sec, and Cys

A

can all be converted to pyruvate

66
Q

catabolic pathway for Asparagine in mitochondria

A

converted to oxaloacetate

67
Q

catabolic pathway for phenylalanine

A

converted to tyrosin (catalyzed by Phe hydroxylase) –> fumarate or acetylCoA

68
Q

phenylketonuria

A
  • best known of the diseases of amino acid metabolism
  • caused by absence or deficiency of Phe hydroxylase
  • phenylalanine accumulates and cannot be converted to tyrosine for complete degradation
69
Q

catabolism of branched-chain amino acids (Leucine, Isoleucine, and valine)

A

yield acetyl CoA, acetoacetate, or succinyl CoA

70
Q

Specialized products that are derived from amino acids

A

nitrogen-containing molecules such as porphyrins, some hormones, neurotransmitters, purines/pyrimidines

71
Q

poryphyrins

A

-cyclic compounds that bind primarily Fe2+ or Fe3+ (heme)

72
Q

Carbon and nitrogen atoms in porphyrins are derived from..

A

glycine and succinyl CoA

73
Q

porphyrias

A

rare genetic disease which lead to defects in biosynthesis of porphyrins and accumulation of intermediates

74
Q

Conversion of amino acids to catecholamines

A

synthesized from tyrosine

-dopamine, norepinephrine, epinephrine

75
Q

Conversion of amino acids to histamine

A
  • mediates many responses (allergic and inflammatory responses, gastric acid secretions)
  • stronf vasodilator
  • formed from decarboxylation of histidine
76
Q

Conversion of amino acids to serotonin (5-hydroxytryptamine)

A
  • synthesized from tryptophan

- pain, sleep, temp, blood pressure, appetite, well-being

77
Q

Conversion of amino acids to creatine

A
  • synthesized from glycine, guanidine group of arginine and Mat
  • small pool of energy source in phosphorylated form

BMSC 230 (15 decks)

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