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SFM > Protein Metabolism > Flashcards

Protein Metabolism Flashcards

1
Q

What is the amino acid pool supplied and depleted by? (3 each)

A

Supplied:

  1. protein turnover
  2. digested food
  3. de novo syn of nonessential amino acids

Depleted:

  1. prod of body protein
  2. syn of nitrogen-containing compounds
  3. degradation
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2
Q
  • autosomal recessive condition that is associated w/ defects in protein transporters
  • defective transport of nonpolar or neutral AAs (e.g. tryptophan), leads to elevated conc in the urine
  • transporter located in kidney and small intestine
  • manifests in infancy w/ failure to thrive, nystagmus, tremor, intermittent ataxia, and photosensitivity
A

Hartnup disease

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3
Q
  • autosomal recessive condition that is associated w/ defects in protein transporters
  • defective transport of dimeric cystine and dibasic AAs: Arg, Lys, and ornithine (COAL)
  • formation of cystine crystals in kidneys (renal calculi)
  • patients present w/ renal colic, abd pain that is intermittent and is similar to kidney stone pain
A

cystinuria

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4
Q

AA biosyn

  • member: aromatic = Trp, Tyr
  • summary:
A

Phe > Tyr

Ribose 5-phosphate > His

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5
Q

AA biosyn

  • member: serine = Ser, Cys, Gly
  • summary:
A

3-phosphoglycerate > Ser > Cys or Gly

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6
Q

AA biosyn

  • member: pyruvate = Ala
  • summary:
A

Pyruvate > Ala

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7
Q

AA biosyn

  • member: Aspartate = Asp, Asn
  • summary:
A

Oxaloacetate > Asp > Asn

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8
Q

AA biosyn

  • member: Glutamate = Glu, Gln, Pro, Arg
  • summary:
A

α-ketoglutarate > Glu > Gln, Pro, Arg

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9
Q
  • type of proteolytic enzyme
  • attacks at C- (carboxypeptidase) or N-terminus (aminopeptidase) ends
  • digests terminal peptide bonds to release amino acids
A

exopeptidase

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10
Q
  • type of proteolytic enzyme
  • attacks within the protein at a specific site, described more specifically by MOA which is dependent on catalytic enzyme in active site
  • digests internal peptide bonds
A

endopeptidase

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11
Q
  • type of intracellular proteolytic control mechanism
  • sequester >50 hydrolase-type intraceullar proteolytic enzymes
  • active at pH 5, inactive at pH 7
  • non-selective
  • 3 types: macro, micro, and chaperone mediated (CMA)
A

lysosomal / autophagy

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12
Q
  • type of intracellular proteolytic control mechanism
  • large ______ cytoplasmic complex that cleaves polyubiquinated proteins > ubiquitin pathway
  • proteins are degraded to peptides and amino acids, which go to different pathways (biosyn, disposal, glucose/glycogen syn, FA syn, and cell respiration)
A

proteasome

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13
Q

What is the extracellular mechanism of proteolysis?

A
  • proteolytic enzymes secreted as inactive zymogens, which are activated by proteolytic cleavage
  • inactive trypsinogen and chymotripsinogen are released into SI lumen
  • trypsinogen activated by enterokinase which creates trypsin
  • trypsin activates chymotrypsinogen and other molecules of trypsinogen
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14
Q

What are the ketogenic amino acids? (2)

A
  1. Leu
  2. Lys

(acetyl CoA or acetoacetate)

(precursors for α-keto acids, ketone bodies, and FA’s)

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15
Q

What are the amino acids that are both ketogenic and glucogenic? (5)

A
  1. Ile
  2. Trp
  3. Phe
  4. Tyr
  5. Thr
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16
Q

What are the glucogenic amino acids? (13)

A
  1. Val
  2. His
  3. Arg
  4. Asn
  5. Gln
  6. Met
  7. Ala
  8. Asp
  9. Glu
  10. Gly
  11. Pro
  12. Ser
  13. Cys

(pyruvate or TCA cycle intermediates (OAA, α-ketoglutarate, succinyl CoA, fumarate)

(precursors for glucose syn via gluconeogenesis)

17
Q
  • enzymes that shuffle amino groups
  • amino group is transferred to an α-ketoacid
  • couple rxns
  • require coenzyme: pyridoxyl-5’-phosphate (PLP) (derivative of vit B6)
  • clinical relevance: ALT and AST liver enzymes
A

transaminases / aminotransferases

18
Q

How are the branch chain amino acids (Val, Ile, Leu) metabolized?

A
  • reduced to intermediates via branched-chain amino acid aminotransferases
  • reduced to isobutyryl CoA (Val), α-methyl-butyryl CoA (Ile), and isovaleryl CoA (Leu) by branched-chain α-keto dehydrogenases (needs CoA, FAD, lipoic acid, NAD, TPP); this is where maple syrup urine disease may occur if there is deficiency in these enzymes or co-enzymes
  • reduced to methacrylyl CoA (Val), tiglyl CoA (Ile), and β-methylcrotonyl CoA (Leu) by acyl CoA dehydrogenases (FAD linked)
  • methacrylyl CoA (Val) converted to propionyl CoA, tiglyl CoA (Ile) converted to propionyl CoA and acetyl CoA; the propionyl CoA then converted to methylmalonyl CoA and then succinyl CoA
  • meanwhile: β-methylcrotonyl CoA (Leu) converted to HMG CoA, then acetyl CoA and acetoacetate
19
Q
  • vitamin deficiencies (B6, B12, folic acid) or genetic defects in enzymes (cystathionine β-synthase) cause defective metabolism of homocysteine
  • risk factor for atheroslerotic heart dz, stroke, thrombosis, and can result in neuropsychiatric illness (vascular dementia, Alzheimer’s)
  • other risks: eye lens dislocation, myopia, osteoporosis, unproportional growth, chest wall deformities, altered facial appearance, mental retardation
  • vit supplementation can normalize plasma homocysteine levels in some cases
A

hyperhomocysteinemia and homocystinuria

20
Q
  • rate autosomal disease resulting from deficient branched-chain α-keto acid dehydrogenase complex (BCKD) activity which results in brached-chain ketoaciduria
  • BC AA’s in urine give hallmark sweet urine smell
  • also accumulate in blood, causing toxic effects and eventual mental retardation
  • tx: synthetic diet limiting BCAA’s (Val, Ile, Leu)
  • BCKD activity may be restored w/ thiamine supps in mild forms of condition
  • death usually within 5 months of birth based upon classification
  • higher in Mennonite, Amish, and Jewish populations
A

maple syrup urine disease

21
Q

What is the general metabolism of Phe?

A
  • Phe is converted to Try by phenylalanine hydroxylase (phenylketonuria)
  • Tyr > p-hydroxyphenylpyruvate (tyrosinemia type II)
  • p-hydroxyphenylpyruvate > homogentisate (tyrosinemia type III)
  • homogentisate > maleylacetoacetate (alkaptonuria)
  • maleylacetoacetate > fumarylacetoacetate
  • fumarylacetoacetate > fumarate and acetoacetate (tyrosinemia type I)
22
Q
  • caused by defects in activity of phenylalanine hydroxylase (PAH)
  • most common IEM, first to be included in newborn screening (post-parturition Guthrie heel prick test)
  • Phe converted to phenylpyruvate and then phenyllactate (musty odor in urine) and phenylacetate
  • later two disrupt neurotransmission, block AA transport to brain, myelin formation, results in severe brain function impairment
  • tx: dietary limit of Phe, synthetic protein supplemented w/ Tyr
  • secondary form of condition results from tetrahydrobiopterin deficiency (cofactor of PAH), defects in syn or regeneration of BH4
A

phenylketonuria

23
Q

derivative of Ser

A

acetylcholine

24
Q

derivative of Glu

A
  • γ-aminobutyric acid (GABA)
25
Q

Derivatives of Tyr (3)

A
  • dopamine > norepi > epi (Parkinsonism)
  • thyroid hormones > triiodothyronine (T3) and thyroxine (T4) (Graves’ dz, hyper/hypothyroidism)
  • melanin (albinism)
26
Q

Derivatives of Trp (2)

A
  • serotonin > melatonin (deficiency in conversion of Trp to serotonin could lead to carcinoid tumors)
  • Trp (needs vit B6) > niacin > NAD+/NADP+
27
Q
  • due to severe lack of melanin
  • conversion of tyrosine to melanin is blocked due to defects in enzyme tyrosinase
  • results in partial or complete absence of pigmentation in skin, hair, and eyes
A

albinism

28
Q
  • 660 kDa portein made by thyroid and used to prod T4 and T3
  • has ~120 Tyr residues, some labeled with iodine (mono and diiodinated Tyr)
  • T4: combo of 2 diiodinated Tyr
  • T3: combo of 1 monoiodinated and 1 diiodinated Tyr (more potent than T4 but shorter half-life)
  • hyperthyroidism tx: carbimazole and propylthiouracil block iodination of thyroglobulin to decrease prod of T4 and T3
A

thyroglobulin and thyroid hormones

29
Q

How is nitrogen removed in the body?

A
  • nitrogen in form of ammonia is removed as Glu and Gln in brain (glutamine synthase) and removed as Glu in other tissues
  • nitrogen in the form of urea is generated in AA metabollic pathways by deamination mechanisms
30
Q

How is ammonium removed from the brain?

A
  • α-KG > Glu (glutamate dehydrogenase)
  • Glu > Gln (glutamine synthase)
  • Gln transported via BS to liver
  • Gln in liver > Glu (glutaminase)
  • excess ammonium excreted via urea cycle
31
Q

How is excess ammonium removed from muscle?

A
  • pyruvate > α-KG and Ala (by ALT)
  • Ala transported via BS to liver
  • Ala in liver > pyruvate which goes into gluconeo to form glucose (by ALT)
  • Ala and α-KG also condensed in liver to Glu
  • ammonium removed from Glu to form α-KG (by GLDH)
  • excess ammonium excreted via urea cycle
32
Q

What are the general steps of the urea cycle?

A
  • NH4+ > carbamoyl phosphate (carbamoyl phosphate synthetase - rate limiting)
  • phosphate group removed from carbamoyl, carbamoyl condensed w/ ornithine to form citrulline (ornithine transcarbamoylase)
  • citrulline leaves mito and enters cyto
  • citrulline condensed w/ Asp > arginino-succinate (argininosuccinate synthetase, uses ATP)
  • arginino-succinate > Arg and fumarate (arginosuccinate lyase)
  • Arg > ornithine and urea (arginase, inhibited by ornithine)
  • cycle continues with ornithine conversion to citrulline

- urea sent via BS to kidneys to be excreted

33
Q

What is the condition associated with defect in ornithine transcarbamoylase (enzyme that condenses carbamoyl and ornithine to form citrulline)?

A

hyperammonemia w/ orotic aciduria (X-linked)

34
Q
  • excessive ammonia due to disorders in urea cycle or liver failure
  • NH3 is toxic agent due to its ability to permeate membranes
  • causes pH imbalance, astrocyte swelling, cerebral edema, intracranial hypertension
  • glutamate dehydrogenase catalyzes ox deamination of glutamate to α-KG, key reactant in TCA; inhibits activity of TCA cycle (disrupts ATP prod)
  • postsynaptic excitatory proteins are inhibited which depresses CNS function
  • depletion of glutamate disrupts neurotransmitter activity (key reactant in form of GABA)
  • also causes mito dysfunction
A

ammonia toxicity

35
Q
  • urea production is increased by a ____ ______ diet and decreased by ____ ____ diet
  • insulin and glucagon play a role in urea production
  • 20-30% of urea prod is hydrolyzed in GI tract by bacterial urease
  • provides nitrogen source for gut bacteria, salvage, and reuse
  • ____ ______ diet enhances prod and hydrolysis
A
  • high protein, high carb
  • high protein

SFM (21 decks)

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