IN PROGRESS

When protein is ingested, the first major digestive process (after chewing, of course) begins in the stomach.  The arrival of chewed food to the stomach signals the release of a peptide-hydrolysing enzyme precursor, called pepsinogen, which is activated by the acid present to produce pepsin.  Proteins require xxx time to be partially broken down by this enzyme.  Smaller peptide chains (oligopeptides) and free amino acids are produced during this time. 

After xxx, the contents of the stomach are released into the duodenum, the starting section of the small intestine where 90-95% of all digestion and absorption of nutrients occur.  Firstly, bicarbonate is release to neutralise the acid.  A new set of peptidase precursors are secreted into the mix by the pancreas and xxx

Amino acid intestinal brush border transporters.

Amino acid digestion

20 Normal amino acids

Unusual amino acids