lecture 5: amino acid metabolism 1 Flashcards
why don’t amino acids have a storage form?
we can convert protein to ATP, still being used
protein turnover
synthesis and degradation of protein
influenced by factors such as oxidation
free amino acid pool remains constant
process that remove AAs = those that add amino acids
S + E = D + I
Positive nitrogen balance S > D
neg S < D
occur at equal rates S = D
how is excess nitrogen removed from the body?
AA breakdown removes nitrogen from body in the form of ammonia or urea
carbon skeletons remaining from removed N can enter TCA cycle
why would a protein turnover be required, even when the body requires no net gain or loss of protein?
replace proteins that have been oxidized, damaged, misfolded
adapt to new physiological and nutritional conditions (muscle breakdown - fasting state, starvation, illness)
which organs have higher protein turnover?
stomach, esophagus, colon - GI tract, replace epithelial lining
liver - metabolism
what individual proteins have higher turnover rates?
regulatory proteins - rapid adaptation of changing conditions
insulin in protein regulation
stimulates protein synthesis, inhibits protein degredation
insulin levels increase with feeding and decrease during fasting
signaling cascade > activation of mRNA translation
insulin protein synthesis activation mechanism
insulin or IGF-1 binds to receptor to stimulate Tyr phosphorylation of IRS-1
IRS-1 activation > stimulates kinases PI3K and pAKT
pAKT inactivates FoxO, which promotes protein breakdown, via phosphorylation > FoxO cannot enter nucleus
pAKT activates mTOR (promotes protein synthesis)
IRS-1
signaling adapter protein that plays a role in transmitting the signal from insulin to various kinases
activation > stimulates pAKT/PI3K
pAKT
kinase that inactivates FoxO, activates mTOR
FoxO
promotes expression of E3 ubiquitin ligases (genes involved in protein degradation), therefore promotes protein breakdown
mTOR
promotes protein synthesis
growth hormone (GH)
promotes longitudinal growth in adolescents
secreted by pituitary gland
initiates signal transduction that promotes expression of anabolic process genes
growth hormone anabolic cascade
GH binds to cell surface receptor, activates JAK2
JAK2 phosphorylates STAT proteins
phos. STAT proteins dimerize and enter nucleus
STAT proteins bind to specific DNA sequences, increasing expression (including IGF-1)