Lecture 6: Protein and Amino Acid Metabolism Flashcards

1
Q

Amino Acid Pool and where they come from/go

A

AA Pool - population of free amino acids (100g)

Come From:

  1. body protein - 400g/day
  2. dietary protein - 100g/day
  3. synthed nonessential AA - varies

Go To:

  1. body protein - 400g/day
  2. porphyrins, creatine, neurotrans, nucelotides - 30g
  3. glucose/glycogen, CO2, urea, FA, ketone - varies
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2
Q

Hartnup Disease

A
  • defective transport of nonpolar/neutral AA (Tryptophan) leads to conc. lvls in urine
    transporter: kidney/small intestine
  • mainifests infancy: failure to thrive, nystagmus, tremor, ataxia, photosensitivity
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3
Q

Cystinuria

A
  • defective transport of dimeric cysteine/dibasic AA (Arg, Lys, Ornithine)
  • form cysteine crystals in kidneys
  • patients present w/renal colic (abdominal pain that comes in waves; linked to kidney stones)
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4
Q

Pyruvate synthesizes what AA?

A

Alanine

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5
Q

G3P synthesizes what AA?

A

Serine, Glycine, Cysteine

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6
Q

Oxaloacetate synthesizes what AA?

A

Aspartate, Asparagine

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7
Q

a-ketoglutarate synthesizes what AA?

A

glutamate, glutamine, proline, arginine

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8
Q

Proteolytic Enzymes

A
  • degradation of proteins for reabsorption

Exopeptidase: attacks at ends (C-terminus/N-terminus)
Endopeptidase: attacks within protein at specific site (internal peptide bonds)

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9
Q

Intracellular Lysosomal vs Proteosomal Proteolytic Control

A

Lysosomal: lysosomes have >50 proteolytic enzymes that are active at pH 5, but inactive at pH 7 (cytoplasmic); NONSELECTIVE

  • protects functional proteins from degradation in case of lysosomal rupture

Proteolytic: degrades polyubiquinated proteins; SELECTIVE

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10
Q

Extracellular Proteolytic Control

A
  • enzymes secreted as needed
  • secreted as inactive zymogens (activated by proteolytic cleavage)
  • enterokinase on intestinal epithelial cell (enteropeptidase) activate trypsinogen to trypsin
  • trypsin activates more trypsinogen, and converts chymotrypsinogen to chymotrypsin
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11
Q

Ketogenic Amino Acids (2)

A

Leucine and Lysine

  • precursors for keto acids, ketone bodies, and fatty acids
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12
Q

Ketogenic AND Glucogenic Amino Acids (5)

A

Isoleucine, Tryptophan, Phenylalanine, Tyrosine, Threonine

  • can make either ketone bodies OR precursors for glucose synthesis/gluconeogenesis (TCA intermediates0
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13
Q

What amino acids make Succinyl CoA?

A

Isoleucine, Valine, Methionine, Threonine

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14
Q

What amino acids make a-ketoglutarate?

A

glutamate

glutamine, histidine, proline ,arginine

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15
Q

What amino acids make fumarate?

A

phenylalanine, tyrosine

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16
Q

What amino acids make oxaloacetate?

A

aspartate and asparagine

17
Q

What is a transaminase reaction and what are the enzymes called?

A
  • the shuffling of amine groups (amino group transferred to an a-ketoacid)
  • coupled rxns that utilizes transaminases (aminotransferases)
  • required coenzyme: PRP (pyridoxyl-5-phosphate)
    • B6 derivative
    • alanine transaminase (ALT)
    • aspartate transaminase (AST)
18
Q

Hyperhomocysteinemia and homocystinuria

A
  • B6, B12, folic acid deficiencies and genetic defects in enzymes cause defective homocysteine metabolism
  • Hyperhomocysteinemia: risk factor in atherosclerotic heart disease, stroke, neuropsychatric illness
  • lens dislocation, osteoprorsis, mental retardation

supplement w/vitamins

19
Q

Maple Syrup Urine Disease

A
  • deficiency in branched-chain-a-keto acid dehydrogenase complex (BCKD)
  • branched chain ketoaciduria (give urine maple syrup smell)
  • blood accumulation causes toxic effect on brain = mental retardation
    treatment: thiamine supplementation, synthetic diet limiting BCAA
20
Q

Phenylketonuria (PKU)

A
  • defects in activity of phenylalanine hydroxylase
  • most common IEM (newborn screening)
  • Phe converted to phenylpyruvate, then phenyllactate (must urine odor) and phenylactate
  • later two disrupt neurotransmission and block AA transport in brain, as well as myelin formation

Secondary PKU –> defects in synthesis/regeneration of BH4

21
Q

What is a cardiac isoform that is used as a diagnostic serum marker for myocardial infarction?

A

creatine kinase (CK-MB)

22
Q

Albinism and Tyrosinase

A
  • albinism due to severe lack of melanin
    (tyrosine –> melanin blocked by defective tyrosinase)
  • also blocked by transfer of tyrosine in the body
  • symptoms: missing pigment in skin, hair, eyes
23
Q

Thyroglobulin and thyroid hormones (hyperthyroidism)

A
  • thyroglobulin used to produce T4/T3

- patients w/hyperthyroidism given agents that block iodination of thyroglobulin (dec. T3/T4 production)

24
Q

Removing Nitrogen from the body (Urea Cycle)

A

Ammonia: removed as Glu/Gln in brain
- removed as Gln/Ala in other tissue

Glutamine (2 amines), glutamate (1 amine) = excreted in urea cycle

25
Q

Ammonia Toxicity

A
  • excessive ammonia due to disorders in urea cycle/liver failure has toxic effects on brain (NH3 toxic)
  • cause pH imbalance, astrocyte swelling (cerebral edema, intracranial hypertension)
  • glutamate –> a-ketoglutarate loses NH4, which inhibits TCA activity and inhibits postsynaptic excitatory proteins (depressed CNS activity)
26
Q

What three AA make creatine?

A

arginine, glycine, methionine

27
Q

Phosphocreatine

A
  • storage form of energy in muscle, brain, and sperm
  • quickly generate ATP

cardioselective isoform of creatine kinase in serum is used as a diagnostic for myocardial infarction