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FHB Exam 3 > Metabolism: Amino Acid Metabolism > Flashcards

Metabolism: Amino Acid Metabolism Flashcards

1
Q

What is the typical level of free AAs in the serum?

A
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2
Q

What is the typical level of free AAs in the serum?

A
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3
Q

What are the sources of free AAs?

A
  • dietary protein
  • biosynthesis of nonessential AAs
  • degradation of endogenous proteins
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4
Q

What are free AAs used for?

A
  • synthesis of endogenous proteins
  • precursors
  • energy (urea is excreted in this process)
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5
Q

Compare nutritionally essential vs nonessential AAs.

A
  • essential = body cannot make them from other precursors

- nonessential = body can make them from other precursors

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6
Q

What are 2 pathways of endogenous protein degradation?

A
  • ATP-dependent ubiquitin proteosome system

- lysosomal

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7
Q

What is the general fate of excess dietary protein?

A

even on a high protein diet, most AAs are degraded, not stored
- transient protein storage after a meal (1/3 meal protein stored)

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8
Q

What is the general fate of excess dietary protein?

A

even on a high protein diet, most AAs are degraded, not stored
- transient protein storage after a meal

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9
Q

What happens to each part of the AA during catabolism?

A
  • N => urea
  • Cs => glucogenic or ketogenic
    • glucogenic = TCA intermediates or pyruvate (glycolysis)
    • ketogenic = aCoA, acetoacetate, acetoacetyl-CoA
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10
Q

What happens to each part of the AA during catabolism?

A
  • N => urea

- Cs => glucogenic or ketogenic

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11
Q

Nitrogen balance = ..

A

N balance = N ingested - N excreted

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12
Q

Describe physiological states where a person might be in positive nitrogen balance.

A
  • growth
  • pregnancy
  • bodybuilding
    ==> protein synthesis > degradation; N is accumulating
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13
Q

Where does urea synthesis occur?

A

liver

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14
Q

Where does urea synthesis occur?

A

liver

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15
Q

What are the sources of free AAs?

A
  • dietary protein
  • biosynthesis of nonessential AAs
  • degradation of endogenous proteins
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16
Q

What are free AAs used for?

A
  • synthesis of endogenous proteins
  • precursors
  • energy (urea is excreted in this process)
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17
Q

Compare nutritionally essential vs nonessential AAs.

A
  • essential = body cannot make them from other precursors

- nonessential = body can make them from other precursors

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18
Q

List the essential AAs.

A
  • arg
  • his
  • ile
  • leu
  • lys
  • met
  • phe
  • thr
  • try
  • val
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19
Q

List the nonessential AAs.

A
  • ala
  • asn
  • asp
  • cys
  • glu
  • gln
  • gly
  • pro
  • ser
  • tyr
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20
Q

What are 2 pathways of endogenous protein degradation?

A
  • ATP-dependent ubiquitin proteosome system

- lysosomal

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21
Q

What is unique about the turnover rate of regulatory proteins?

A

degraded and resynthesized at a faster rate

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22
Q

What is the general fate of excess dietary protein?

A

even on a high protein diet, most AAs are degraded, not stored
- transient protein storage after a meal

23
Q

How much is obligatory protein degradation?

A

55g

thus, dietary protein must supply 55g to remain in net balance

24
Q

What happens to each part of the AA during catabolism?

A
  • N => urea

- Cs => glucogenic or ketogenic

25
Q

Nitrogen balance = ..

A

N balance = N ingested - N excreted

26
Q

Describe physiological states where a person might be in positive nitrogen balance.

A
  • growth
  • pregnancy
  • bodybuilding
    ==> protein synthesis > degradation; N is accumulating
27
Q

Describe physiological states where a person might be in negative nitrogen balance.

A
  • starvation (protein malnutrition)
  • trauma
  • infection
  • infection, sepsis
  • cancer
  • burn
    ==> protein degradation > synthesis; N is being lost; muscle mass decreases
28
Q

Where does urea synthesis occur?

A

liver

29
Q

Describe the transamination reaction in urea production.

A
  • first step
  • AA-NH2 + alpha-ketoglutarate => aminotransferase => glutamate
  • occurs for ALL AAs catabolism
30
Q

What is the cofactor for aminotransferase?

A

pyridoxal phosphate (B6)

31
Q

Why are serum ALT/AST used in diagnosis?

A

if there is tissue damage, cytosolic contents of cells are released. These particular transaminases (alanine and aspartate) are found in the cytosol and if they are increased in the serum it indicates damage

32
Q

What is the 2nd step in urea production?

A

glutamate => aspartate + NH4

- high levels of glu push the reaction of aspartate transaminase in the opposite direction

33
Q

Describe genetic hyperammonemia.

A

due to genetic deficiency of a urea cycle enzyme

34
Q

How does glutamate produce ammonia?

A

glu + NAD => glu dehydrogenase => NH4 + alphaketoglu + NADH

35
Q

What is the major regulated step of urea synthesis?

A
  • formation of carbamoyl phosphate via carbamoyl phosphate synthetase I
  • Carbamoyl phosphate is a requirement for N-acetylglutamate to function
36
Q

List the steps involved in the urea cycle.

A
  1. NH4 => carbamoyl phosphate via carbamoyl phosphate synthetase and N-AG
  2. CP + ornithine => citrulline via ornithin transcarbamylase
  3. citrulline + asp => argininosuccinate via argininosuccinate synthetase
  4. => arg + fumarate via argininosuccinate lyase
  5. arg => urea + ornithine via arginase
37
Q

What is the overall reaction for urea cycle?

A

NH3 + asp + CO2 + 3 ATP + 3 H2O => urea + fumarate + 2 ADP + AMP + 4 Pi

38
Q

Where are the urea cycle enzymes located?

A
  • carbamoyl phosphate synthetase = mitochondria
  • ornithine transcarbamylase = mitochondria
  • all others are cytosol
  • ornithine enters mito and citrulline leaves via shuttle exchanger
39
Q

What is the role of N-AG?

A

activates carbamoyl phosphate synthetase

- high glutamate levels cause glutamate acetylation which binds to CPS and alerts the system of the need to detoxify NH3

40
Q

Describe activation of urea cycle.

A
  • high glutamate => high N-AG => high urea production

- high protein diet => high levels of urea enzymes

41
Q

How is nitrogen delivered to the liver?

A

via alanine and glutamine

42
Q

What is the normal BUN level?

A

7-30 mg/dL

43
Q

What does an increased BUN indicate?

A 
renal disease
GI bleeding
leukemia
dehydration
UT obstruction
44
Q

What does a decrease in BUN indicate?

A

pregnancy
liver failure
acromegaly

45
Q

What is the function of urea synthesis?

A

ammonia detox

46
Q

What can hyperammonemia lead to?

A

liver failure
coma
hepatic coma

47
Q

Describe acquired hyperammonemia.

A
  • due to portal-systemic shunting
  • ## leads to portal-systemic encephalopathy
48
Q

Describe genetic hyperammonemia.

A

due to genetic deficiency of a urea cycle enzyme

49
Q

Describe protein balance during fed state.

A

overall = synthesis

- in muscles, AAs and insulin promote synthesis and inhibit degradation

50
Q

Describe protein balance during starvation/overnight fast.

A

overall = degradation

  • lack of AAs and insulin leads to protein degradation
  • AAs go to the liver for gluconeogenesis (influenced by glucagon)
51
Q

Which AAs are ketogenic?

A

leucine

lysine

52
Q

Which AAs are both gluco and ketogenic?

A 
ile
phe
thr
trp
tyr
53
Q

Is arginine essential or nonessential?

A

semiessential

- can be made but not sufficient enough for growing children

54
Q

Is it okay to be deficient in one essential AA?

A

no b/c all proteins require all AAs so if you are missing one it will disrupt protein synthesis

FHB Exam 3 (23 decks)

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