Protein and AA metabolism

Question 1

where do the amino acids in the “AA pool” come from?

Answer 1

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

Question 2

Where do the amino acids in the “AA pool” go?

Answer 2

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

Question 3

Exopeptidase definition

Answer 3

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

Question 4

Endopeptidase definition

Answer 4

proteolytic enzyme that attacks within the protein at internal peptide bonds

endo = inside attack, splits proteins

Question 5

intracellular proteolytic control (2 ways)

Answer 5

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)

Question 6

extracellular proteolytic control

Answer 6

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

Question 7

Essential AA (10)

Answer 7

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

Question 8

just ketogenic AA

keto/gluco

just glucogenic AA

Answer 8

Leu, Lys = “fat Loss in keto diet)

Ile, Trp, Phe, Tyr, Thr = “I wipe with TP”

all the rest of the AA

Question 9

what do transaminase reactions do?

Answer 9

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

Question 10

hyperhomocysteinemia and homocysteinemia

Answer 10

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

Question 11

maple syrup urine disease

Answer 11

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

Question 12

phenylketonuria

Answer 12

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

Question 13

albinism

Answer 13

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

absence of skin/hair/eye pigmentation

Question 14

urea cycle

Answer 14

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

Question 15

ornithine cycle

Answer 15

also known as the urea cycle

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

Question 16

ammonia toxicity

Answer 16

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

Question 17

creatine is made from three AA

Answer 17

Arg, Gly, Met