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Met.biochem L5

Proteins as micronutrients -AA catabolism

AA -1/2 syn -1/2 diet -40-50g daily requirement
protein degradation -all involve proteinases -in cyt. -catalysed by calpains or proteasomes
cathepsins -lysosomal proteinases -recycle aa from protiens
digestion of AA -pepsin digestion -acid denaturation & hydrolysis
pepsin -secreted as pepsinogen(inactive zymogen) -stomach acids modify (active)
enterokinase attaches... -to membrane of enterocyte which activate trypsinogen -causes cascade of proteinases
Active chymotrypsin -N-term + charge -forms ionic link W aspartic acid
action of peptidases -hydrolyse peptide bonds -in brush borders -active/facilitated diffusion
Digestibility of proteins -high efficiency -proteinase inhibitors prevents digestion
Turnover of proteins -7/8 essential aa recycled -300g aa endogenous -100g from diet
Nitrogen balance (-ve) -starvation -short term -decr intake -red. GI fn
Nitrogen balance (+) -children & pregnant -utilise to support protein syn. & growth
equilibrium -healthy adults -min=30-50g
essential AA -must be oresent in diet -his,leu,met,thr,val,ile,lys,phe,trp
his&arg -semi-essential -adults make enough but rate is too low
requirement for met... -can be made by cysteine + CH3 + v.v
Tyr can be made from -phe
limiting AAs -all aa must be present for syn. -continually supplied from diet -aa catabolised if not used
complementary proteins -2 low quality -combine to give overall aa balance
Created by: meglet