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Met.biochem L5
Proteins as micronutrients -AA catabolism
| Question | Answer |
|---|---|
| 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
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