protein

• Alanine: gluconeogenic AA, nonessential, needs N group from previous AA
• Valine, Leucine, Isoleucine: branched chain AA (BCAA), essential
• Tyrosine: semi-essential, aromatic ring
• Methionine: essential, sulfur containing

  Cysteine: semi-essential, sulfur containing
• Asparagine: nonessential, made from oxaloacetate (OAA), carboxamide (has amino N)
• Glutamine: nonessential, made from glutamate (alpha-KG) in the TCA cycle
• Glutamate: nonessential, alpha-KG, negative charge
• Peptide bonds: links between alpha-carboxylic group of one AA and the alpha-amino group of another AA
• Non-enzymatic modifications of AA side chains: glycation can accumulate over time, HbA1c used to monitor blood glucose
• Nonproteinogenic AA: from catabolism of proteinogenic AA
• protein is denatured by HCl, activates G cells to release gastrin = more HCI
• pepsin hydrolyzes peptide bonds, pepsinogen released from chief cells
• CCK tells pancreas to release proenzymes into duodenum
• duodenal enterocyte releases enteropeptidase to activate proenzymes
• Proenzyme: trypsinogen activates into trypsin which causes a cascade activation of other proenzymes
• Endopeptidases: target the internal peptide bonds, trypsins and elastases (pancreatic)
• Exopeptidases: target ends of polypeptides, carboxypeptidases A and B (pancreatic)
• Brush border peptidases: aminopeptidase and dipeptidase, turn oligopeptides into tripeptides, dipeptides and AA
• Enterocytes use or release AA, only free AA can leave the enterocyte into the portal blood
• PepT1 transporter: primary transporter for peptide uptake in enterocytes
• a mixture of dipeptides and tripeptides is absorbed more efficiently than a free amino acid mixture
• Exocrine pancreatic insufficiency: not breaking down polypeptides, people are given di, tri, and AAs
• Hartnup disease: disorder of B0 transport system, transports tryptophan, leads to no synthesis of niacin (not enough NAD created for TCA and ETC)
• Enterocytes use glutamine rather than glucose for fuel and substrate