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GI > Protein Degradation > Flashcards

Protein Degradation Flashcards

1
Q

Two systems of protein degradation

A

extracellular

intracellular

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2
Q

EC Protein Degradation

A

diet: proteins –> epithelial cells of SI (absorption)–> liver (by the portal vein for processing): AAs

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3
Q

4 steps of protein catabolism

A
  • 1) degradation of proteins to AAs
  • 2) removal of AA group
  • 3) elimination of ammonia (urea)
    4) fate of the carbon chain…
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4
Q

Which can be stored?

fat, carb, protein

A

only fat and carb can be stored (protein/AAs/ammonia cannot be stored)

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5
Q

What happens to AAs of protein?

A

Carbon chain goes for storage but NH3 gets excreted

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6
Q

What are 2 roles of trypsin?

A

cut proteins in diet; cut other proteases (zymogens)

-lacks protein target specificity

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7
Q

Why is no ATP required for absoprtion of proteins?

A

Acidity of gut environment

In cells, you need ATP to de-fold proteins

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8
Q

Describe the transamination reaction

A

take nitrogen group from alpha amino acid from diet and add it to glutamate using AMINOTRANSFERASE (multiple)

*converted AA to ketoacid, which is basically a carbon chain

  • no energy requirement,
  • fully reversible
  • no energy needed
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9
Q

What is the essential co-factor required for transamination reaction?

A

pyridoxal phosphate (B6 derivative)

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10
Q

What are the 3 important AA/Ketoacid pairs (that feed into TCA)?

A

1) glutamate alpha-ketoglutarate
2) alanine pyruvate
3) aspartate oxaloacetate

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11
Q

What is the role of “glutamate alpha-ketoglutarate” ?

A

transamination

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12
Q

What is the role of alanine pyruvate?

A

glucose-alanine cycle: capture of ammonia in peripheral tissue and safe transportation of that ammonia to the liver

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13
Q

What is the role of aspartate oxaloacetate?

A

urea cycle (donates second nitrogen into the cycle)

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14
Q

Why the tight coupling btwn AA breakdown and TCA?

A

energy requirement (depletion)

these are the sensors to tell you time to start breaking down protein:

1) glutamate alpha-ketoglutarate
2) alanine pyruvate
3) aspartate oxaloacetate

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15
Q

What is arginine’s effect on S-ethyglutamate (cofactor for CPS1)?

A

stimulates as [arg] increases

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16
Q

CPS1

A

rate limiting factor in pathway

17
Q

Why is the urea cycle irreversible?

A

1) energy requirement

2) compartmentalized

18
Q

How is urea cycle regulated?

A

-positively regulated:

arg positively regulates cofactor for CPS1 (RLS enzyme)

19
Q

What is the nitrogen source for the urea cycle?

A

glutamate (directly and indirectly)

20
Q

What is the net effect in step(s) of urea cycle?

A

hyperammonenemia

eg: Mutation in CPS1

21
Q

What is the physiological response to sudden “pulse” of ammonia?

A

1) attach ammonia to pyruvate and make alanine –> transport to liver –> catalyze hydrolysis there

22
Q

What are key enzymes only expressed in liver?

A

asparginase, glutaminase, arginase, CPS1

23
Q

Which reactions require: Vitamin B6 (pyridoxal phosphate)?

A

x

24
Q

Which reactions require: S-adenosyl methionine?

A

x

25
Q

Which reactions require: tetrahydrobiopterin?

A

x

26
Q

Which reactions require: folate?

A

x

27
Q

Which reactions require: Vitamin B12 (methylcobolamin)?

A

x

28
Q

What is the RLS of the urea cycle?

A

x

Enzyme: CPS1

29
Q

What is the ALLOSTERIC EFFECTOR of the urea cycle?

A

X

30
Q

How is energy coupled to nitrogen incorporation in the urea cycle?

A

x

31
Q

What are the dedicated enzymes of the urea cycle?

A

LIVER: arginase, asparinginase, glutaminase, CPS1

32
Q

How would a spike in ammonia levels be temporarily controlled?

A

glutamate –> glutamine

33
Q

Whats the difference btwn glutamate dehydrogenase and aminotransferase?

A

x

34
Q

What are 3 liver-specific enzymes that are involved in ammonia metabolism?

A

x

35
Q

What is the effect of mutations in CPS1 and N-acetylglutamate synthase?

A

x

36
Q

What are 3 reactions that primarily occur in the liver relating to the urea cycle?

A

glutamine –> glutamate;
asparagine –> aspartate;
glutamate –> alpha-KG

GI (17 decks)

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