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SFM > (L6) Protein and AA Metabolism > Flashcards

(L6) Protein and AA Metabolism Flashcards

1
Q

How are AAs supplied to and depleted from the body supply of AAs?

L6 S7 LO1

A

Supply:

  • degradation of protein
  • dietary
  • synthesis of AAs

Depletion:

  • production of proteins
  • synthesis of nitrogen compounds
  • degradation of AAs
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2
Q

What is Hartnup disease?

L6 S7 LO1.a

A

Autosomal recessive defect in transporter for nonpolar/neutral AAs

Transporter found in the kidney and SI

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3
Q

How does Hartnup disease present?

L6 S7 LO1.a

A

Manifest as an infant

-failure to thrive

  • nystagmus
  • tremor
  • ataxia (intermittent)

-photosensitivity

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4
Q

What is cystinuria?

L6 S7 LO1.a

A

Autosomal recessive defect in transporter for dimeric cystine and dibasic AAs

resluts in cystine cyrstals in kindeys which form renal calculi

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5
Q

How does cystinuria present?

L6 S7 LO1.a

A

Abdominal pain that comes in waves linked with formation of kidney stones, renal colic

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6
Q

What are exopeptidases and endopeptidases?

L6 S12 LO1.b

A

Exopeptidase:

-cleaves peptide bond from either the C or N terminus

Endopeptidase:

-cleaves peptide bond at specific site within protein

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7
Q

What are the major intracellular pathways of protein degradation?

L6 S13 LO1.c,d

A

Lysosomal/autophagy:

  • non-selective
  • occurs in the lysosome and requires acidic pH (~5)

Proteasomal:

  • selective; requires protein to be ubiquinated
  • occurs in cytoplasm by proteasome complex
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8
Q

What is the extracellular pathway of protein degradation?

L6 S14 LO1.d

A

Secreted, inactive zymogens which are activated by enterokinases

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9
Q

What are the different AA synthesis families?

L6 S11 LO1.f

A
  • Pyruvate
  • Glutamate
  • Aspartate
  • Serine
  • Aromatic
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10
Q

What is the difference between ketogenic and glucogenic amino acids?

L6 S17 LO2.a

A

Ketogenic:

-can be converted into precursors for keto acids, ketones, or FAs (eg. acetyl CoA and acetoacetate)

Glucogenic:

-can be converted into precursors for gluconeogenesis (eg. pyruvate or TCA intermediates)

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11
Q

What are the ketogenic only amino acids?

L6 S17 LO2.a

A
  • Leucine
  • Lysine
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12
Q

What amino acids are both ketogenic and glucogenic?

L6 S17 LO2.a

A
  • Isoleucine
  • Phenylalanine
  • Tryptophan
  • Tyrosine
  • Threonine

I Pee 3 Times

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13
Q

What is the reaction catalyzed by ALT?

L6 S21-22 LO2

A

Alanine aminotransferase

Pyruvate + Glutamate -> Alanine + α-ketoglutarate

Uses PLP (vitamin B6)

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14
Q

What is the reaction catalyzed by AST?

L6 S21-22 LO2

A

Aspartate aminotransferase

OAA + Glutamate -> Aspartate + α-ketoglutarate

Uses PLP (vitamin B6)

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15
Q

What is the reaction catalyzed by GA?

What is the significance of this?

L6 S21;23 LO2

A

Glutamine aminohydrolase

Glutamine + H20 -> Glutamate + NH3

Used to sequester free nitrogen in the brain.

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16
Q

What is hyperhomocysteinemia?

L6 S26 LO2

A

Results from deficiencies in cofactors (B6, B12, folic acid) or enzymes (cytationine β-synthase) that cause build up of homocysteine

Risk factor for ASHD, stroke, Alzheimer’s, lens dislocation, osteoporosis, and MR

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17
Q

What is maple syrup urine disease?

L6 S28 LO2

A

Autosomal recessive disease resulting from deficiency of branched-chain

α-keto acid dehydrogenase (BCKD) which is responsible for degrading branched chain AAs (isoleucine, leucine, and valine).

High concentrations of these AAs in the urine give it a smell simialr to maple syrup.

Treatment is limiting intake of these AAs.

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18
Q

What is the mechanism of phenylketonuria and how is it treated?

L6 S29 LO2

A

Defect in phenylalanine hydroxylase (PAH) which converts Phe into Tyr

Phenyllactate and phenylacetate are instead produced which block AA transport into brain and prevent myelin formation.

Treatment in limitation of Phe consumption with supplementation of Tyr

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19
Q

What are notable tryptophan derivatives?

L6 S34 LO3

A

Niacin

  • requires B6
  • used in NAD+/NADP+

5-hydroxytryptophan

  • requires B6
  • used in serotonin which is also used in melatonin
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20
Q

What are notable tyrosine derivatives?

What diseases are realized to tyrosine derivatives?

L6 S35 LO3

A

T3 and T4

-Graves’ disease and hyper/hypothyroidism

Melaninin:

-Albinism

Dopamine:

-Parkinson’s

Norepinephrine/epinephrine

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21
Q

What are notable arginine derivatives?

L6 S36 LO3

A

Creatine, creatine phosphate, and creatinine

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22
Q

How is ammonia removed from the brain?

L6 S40 LO4

A

α-ketoglutarate is aminiated to glutamate and glutamate is aminated to glutamine

Glutamine in shuttled to liver

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23
Q

How is ammonia removed from muscle?

L6 S41 LO4

A

Alanine is aminiated using ALT Alanine is shuttled to liver

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24
Q

What is the mechanism of ammonia toxicity?

L6 S45 LO4

A

Ammonia is able to cross cell membranes as it is uncharged (unlike ammonium)

This causes a pH imbalance, most notably in astrocytes in the brain resulting in:

  • cerebral edema
  • intracranial hypertension

TCA cycle is also disrupted due to depletion of α-ketoglutarate

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25
Q

What is the rate limiting step of the urea cycle?

Where does this occur?

L6 S43 LO4

A

Carbamoyl phosphate synthetase (in the mitochondria of the liver)

uses ammonium, bicarbonate, and ATP to form carbamoyl phosphate

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26
Q

Essential AA

A

pvt: phenylalanine, valine, threonine

Tim: tryptophan, isoleucine, methonine

hall: histadine, arganine, leucine and isoleucine

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27
Q

Phenylalanine makes

A

Tyrosine

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28
Q

ribose-5-phosphate makes

A

Histidine

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29
Q

Pyruvate makes

A

alanine

30
Q

3 phosphoglycerate makes

A

serine –> cystine or glycine

31
Q

Oxaloacetate makes

A

asparate –> asparganine

32
Q

alpha-ketoglutarate makes

A

glutamate –> glutamine, proline or arginine

33
Q

Exopeptidase vs endopetidase

A

attacks within the protein at a specific site

34
Q

Intracellular proteolytic control

A

enzymes are controlled through marking mech that tags their protein substrates for degradation, this keeps intracellular enzymes from indicsimiatley degrading functional proteins

2 Types:

  • Lysosomal/Autophagic System
  • Protesomal degredation
35
Q

Lysosomal/Autophagic System

A

have >50 hydrolase intracellular enzymes
-activate at pH of 5 in lysozme and inactive at pH of 7 (cytoplasmic)

  • enzymes are nonslective
  • 3 types: macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA)
36
Q

Intracellular proteolytic control: CMA

A

Chaperone mediated autophagy: specifically recgonizes substrate

37
Q

Intracellular proteolytic control: macroautophagy

A

uses multivesciular bodies (MVBs) to selectively deliver ubiqinated membrane proteins together with extracellular components to lysosomes

38
Q

Intracellular proteolytic control: proteasomal degradation

A

proteasomal degradation: large proteasome cytoplasmic complexes that cleave polyubqinated proteins (selective pathway)

  • catalytic core 20S with 7 subunits stacked on top of each other fo form a barrel
  • OH of threonine acts as a nucleophile to attack carbonyl of peptide bonds
39
Q

Extracellular proteolytic control

A
  • proteolytic enzymes are secrated when needed
  • secreted as zymogens and activated by proteolytic clevage

EX:

  • inactive tryspinogen and chymo are releasead in SI lumen
  • then ENTROKINASE is secreted and activates trypsin which activates chymo
40
Q

glucogenic AA

A

the rest

-goes to become pyruvate or TCA cycle intermediates (turned into glucose via gluconeogensis)

41
Q

Basic AA vs acidic aa

A

cysteine, orthine, arginine, cystine

asp, glu

42
Q

AA metaoblism

A

1) Aminotransferases/ transaminase (ALT/AST) will transfer an amino group from the AA to a keto acid to make glutamate
2) glutamate dehydorgenase will act on glutamate via Nad–> NADH and produce NH4+

3) NH4 will enter the urea cycle
- the amine is shuffeled into the liver and repackaged as urea in the urea cycle

43
Q

Transaminases need what?

A

-require coenzyme: pyridoxyl 5’ phosphate (a derivate of vitman B6)

44
Q

How is alpha-ketoglutarate replenished?

A

Alpha-ketoglutarate is replenished by the anaplerotic reaction: glutamine -> glutamate -> alpha-ketoglutarate

-(glutaminase (a hydrolase) converts glutamine to glutamate and releases an NH4+)

Reverse Rxn:
-glutamine synthase takes on a NH4 to trap the nitrogen

-his, arginine and proline also can do this

45
Q

What cofactor is shared with transaminases and cistionine beta synthase?

A

Pyridoxal phosphate (PLP)

46
Q

Homocytinuria

A

Normally if all enzymes are working homocysteine is turned into MET

caused by 2 things:
-cystathionine beta-synthase mutation (needs Pyridoxal phosphate (PLP) as a coenzyme)

  • HOMOCYSTEINE methyltransferase deficiency (needs vit b12)
  • this causes hyperhomocysteinemia as it is built up as it can not get degraded
47
Q

hyperhomocysteinemia and homocystinuria

A

Vitamin deficiencies (B6 (PLP), B12, folic acid) or genetic defects in enzymes (cystathionine β-synthase) cause defective metabolism of homocysteine

48
Q

Hyperhomocysteinemia Sx

A
  • risk factor for atherosclerotic heart disease
  • stroke
  • neuropscyh illnesses
49
Q

BCAA Catabolism

A

Valine –> turned into succinyl CoA (Glucogenic)

Isoleucine –> can produce succinyl CoA and acetyl coa as it is both

leucine can produce acetoacetate and acetyl coa

ENZYME THAT ACTS ON IT IS ALPHA KETO ACID DEHYDROGENASE –> AND IT DOES OXIDATIVE DECARBOXYLATION

Deficiencies of these pathways can lead to maple syrup disease

50
Q

Maple syrup urine disease (MSUD)

A

-rare autosomal diseases resulting from deficient branched-chain α-keto acid dehydrogenase complex (BCKD) activity which results in branched-chain ketoaciduria.

-Branched-chain amino acids present in the urine give the hallmark maple syrup smell.
Also accumulate in blood causing toxic effects on brain function and eventually mental retardation.

  • treatement includes snythetic diet limiting BCAA
  • Higher in Mennonite, Amish and Jewish populations
51
Q

Metabolism of Phenylalanine

A

-Phenylalanine turns into tyrosine which turns into fumurate eventually

  • this is done by phenylalanine hydroxylase
  • deffiency in phenyalanine hydroxylase leads to –> (PKU)
52
Q

Phenylketonuria

A

-PKU is caused by defects in the activity of phenylalanine hydroxylase (PAH)
Most common IEM; first IEM to be included in newborn screening

  • Dietary limit Phe, protein supplied with synthetic formula supplemented with Tyr.
  • Secondary PKU resulting from tetrahydrobiopterin deficiency (a cofactor of phenylalaninie hydroxlyase). Defects in synthesis or regeneration of BH4.
53
Q

Most common IEM. What is a common symptom with it?

A

PKU. MUSTY ODOR IN URINE.

54
Q

Tyrptophan AA derivative

A

can produce:
trp –> seritonin –> melatonin
trp —> nicanin —-(VIA vit b6)—-> nad+/NADP+

55
Q

tyrosine AA derivates

A
  • dopanine –> nor ep –> epi
  • thryoid hormones (t3 and t4)
  • melanin
56
Q

Ketogenic AA

A

leucine and lysine

-goes to acetyl CoA or acetoacetate (eventually turned into ketone bodies and can not be turned into glucose)

57
Q

Ketogenic and Glycolytic AA

A

Isoleucine, tryptophan, penylalanine, tyrosine, threonine (PITTT)

58
Q

Creatine

A
  • made from arginine, glycine, and methionine
  • 1-2% is creatine phosphate (CP)
  • excreted in the urine
  • elevated serum levels of CP means kidney dysfunction and muscle degradation
  • CP serves as energy storage in muscle, brain, and sperm
  • it quickly generates ATP, and is used as our immediate energy source
  • Cardiac isoform creatine kinase (CK-MB) diagnostic for MI

-can be turned into creatine, nonenzymatically

59
Q

What is albimsim caused by?

A
  • Albinism is due to severe lack of melanin
  • Conversion of tyrosine to melanin is blocked due to defects in the enzyme tyrosinase
  • Results in partial or complete absence of pigmentation in skin, hair and eyes
60
Q

Thyroglobulin and thyroid hormones

A
  • Thyroglobulin is a 660 kDa protein made by the thyroid and is used to produce T4 and T3
  • T4 is the combination of 2 diiodinated Tyr
  • T3 is the combination of 1 monoiodinated and 1 diiodinated Tyr; more potent than T4 but shorter half-life

If you cant make T3 and T4 –> Can cause Hypothyroidism –> which can lead to graves disease.

61
Q

Hypothyroidism vs Hyper thyroidism

A

  • High TSH, low T4
  • Low TSH, high T4/3
62
Q

Urea Sx

A

hepatic enceoplatophice, neurologica problems, toxic encphalophties

63
Q

Removal of excess nh4 from brain

A

alpha keto gluterate -(glutamate dehydrogenase)-> glutamate -(glutamine synthase)-> Gln (carries the Nh3 out)

  • Gln is than taken to the liver and turned into glu
  • the free NH4 released by the glutimase then enters the urea cycle
64
Q

What happens if there is to much ammonium

A

Glutamate dehydrogenase (GADH) keeps going on and on till it depletes the pool of alpha ketogluterate (CTA METABOLITE) and depletes ATP

65
Q

Removal of excess nh4 from the muscles

A
  • 1) pyruvate and glutamate react to form alanine and alphaketogluterate via (alanine aminotransferase with the coenzyme PLP)
    (TRANS AMINATION RXN)

-2) ALANINE is then transfered to the blood then liver and then alanine and alpha ketogluterate come toghether and form pyrvate and glutamate
(TRANS AMINATION RXN)

-glutamate is then turned into alpha ketogluterate by glutamate dehydrogenase
(OXIDATIVE DEMAINATION RXN)

66
Q

What is the RLS of the urea cycle and where does it happen?

A

MITOCHONDRIA OF THE LIVER (some times in kidney)

STIMULATED BY NAG……..

67
Q

Removing nitrogen: ammonia

A
  • Ammonia is removed as Glu and Gln in the brain via glutamine synthase
  • it is removed as gln and ala in other tissues
68
Q

Where is urea fromed

A

primarly liver but sometimes kidneys. It is excreted by the kindeys.

69
Q

Urea cycle STEP ONE

A
  • NH4 is turned into carbamoylphosphate via carbamoyl phosphate synthetase
  • this step is rate limiting
  • requires a bicarbonate and 2 ATP
70
Q

What causes hyperammonemia?

A

Carbamoyl phosphate synthetase 1 deffiency

71
Q

Ammonia tocitity slide****

A
72
Q

Urea cycle and the high protein diet

A

urea production is increased by a high protein diet and decreased by high carb diet.

  • Insulin and glucagon play a role in urea production
  • About 20-30% of urea produced is hydrolyzed in the GI tract by bacterial urease
  • Provides a source of ammonia nitrogen for gut bacteria, salvage and reuse
  • High protein diets enhances this production and hydrolysis

SFM (31 decks)

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