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Flashcards in Protein and AA metabolism Deck (17):

where do the amino acids in the "AA pool" come from?

the AA come from dietary intake, protein turnover inside the body, and de novo synthesis of new nonessential AA inside the body


Where do the amino acids in the "AA pool" go?

Approximately the same amount that came from protein turnover inside the body go back into the body, some AA are used to synthesize creatine, neurotransmitters, nucleotides, and some go into the pathways that create glucose/glycogen, CO2, urea, ketone bodies, fatty acids and steroids depending on metabolic needs


Exopeptidase definition

exopeptidase is a proteolytic (degrades protein) by attacking the C (carboxypeptidase) or N (aminopeptidase) terminus of the protein

Think exo = attacks at end, shortens proteins


Endopeptidase definition

proteolytic enzyme that attacks within the protein at internal peptide bonds

endo = inside attack, splits proteins


intracellular proteolytic control (2 ways)

1) lysosomes house over 50 hydolase-type proteolytic enzymes that are non-selective, but function at 5pH (found inside lysosome). These enzymes are non functional at cytosolic pH7. When a protein is sent/enters the lysosome it will get degraded.

2) there are also large proteasome complexes in the cytosol that cleave polyubiquinated (marked for degradation)


extracellular proteolytic control

inactive forms of proteolytic enzymes (zymogens) are secreted as needed and are only activated by enterokinase which is found on the small intestinal epithelial cell surface


Essential AA (10)

Met, Thr, Val, Phe, Ile, Trp, Lys, Leu, His, Arg


just ketogenic AA


just glucogenic AA

Leu, Lys = "fat Loss in keto diet)

Ile, Trp, Phe, Tyr, Thr = "I wipe with TP"

all the rest of the AA


what do transaminase reactions do?

these rxns (enzyme also called aminotransferases) shuffle the amino group from an AA to an alpha-ketoacid (ie a-ketoglutarate) and are coupled reactions/reversible between a-ketoacids and AA.

These reactions require PLP which is a derivative of vitamin B6 so would be effected by a B6 deficiency


hyperhomocysteinemia and homocysteinemia

are deficiencies in B6, B12 and/or folic acid OR are genetic defects in cystathionine B-synthase needed for methionine degradation (makes homocysteine).

risk factors for heart disease (atherosclerosis)/stroke/lens dislocation/osteoperosis

corrected via vitamin supplements


maple syrup urine disease

autosomal recessive
deficient BCKD
maple syrup urine smell, BCAAs accumulate in blood, higher in mennonite, amish, jewish communities



PKU is caused by deficiency in phenylalanine hydroxylase (PAH)
disrupted neurotransmission and impaired myelin formation = severe brain impairment



severe lack of melanin caused by defects to tyrosinase enzyme (usually would convert tyrosine to melanin)

absence of skin/hair/eye pigmentation


urea cycle

removes nitrogen from body by making urea or ammonia

in the brain nitrogen (NH4+) is removed in the form of Glu (glutamate) and Gln (glutamine) since Gln can cross BBB into blood and into liver

in tissues nitrogen (NH4) is removed as Gln and Ala since Ala can cross into blood supply and into liver


ornithine cycle

also known as the urea cycle

happens in liver mitochondria and cytosol. creates urea (that is sent to kidneys via blood for excretion)


ammonia toxicity

liver failure or urea cycle failures can lead to increase toxic ammonia levels which cause pH imbalances in the brain and lead to cerebral edema/intracranial hypertension. inhibits glutamate dehydrogenase (in TCA) which depresses ATP production. neurotoxicity


creatine is made from three AA

Arg, Gly, Met