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nbme24/Block 2/Question#48

The breakdown of dipeptides and tripeptides to free ...

Intestinal mucosa

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 +64  upvote downvote
submitted by seagull(432),

The semantics of this question made me vomit blood.

One day a patient will look me in the eyes and ask, "Where are tripetides broken down?" I will smile at them and say, "the intestinal mucosa and not the duodenum." They'll smile back and I'll walk away and think of this moment as I jump from the window.

sympathetikey  Too real. +2  
mcl  how do i upvote multiple times +6  
trichotillomaniac  I made an account solely so I could upvote this. +4  
dragon3  ty for the chuckle +1  
cinnapie  @trichotillomaniac Same +2  




 +12  upvote downvote
submitted by drdoom(207),

The duodenal lumen (and pancreatic proteases like CHYMOTRYPSIN) is the site where pancreatic enzymes (“endopeptidases”) cleave large polypeptides into smaller bits (=dipeptides,tripeptides). It is at the BRUSH BORDER where the smallest kinds of peptides (dipeptides,tripeptides) are broken down into their amino acids, which finally can be co-transported with Na+ into the intestinal cell.

I think about it this way:

  • stomach acid denatures and “opens up” proteins (without specific cleavage);
  • pancreatic enzymes then cleave denatured polypeptides into smaller bits;
  • brush border enzymes finally break down tiniest peptides into absorbable amino acids.




 +1  upvote downvote
submitted by seagull(432),

The semantics of this question made me vomit blood.

At least one day a patient will look me in the eyes and ask " where are tripetides broken down at". I will smile at them and say "the intestinal mucosa and not the duodenum". They'll smile back and then i'll then i'll walk away and think of this moment as I jump from the window.





Why is duodenal lumen incorrect? I thought pancreatic enzymes (chymotrypsin, carboxypeptidase) would be located here.

colonelred_  Enterokinase actives trypsinogen and is located closer to the intestinal mucosal (“brush border”). +  
drdoom  Yeah, @colonelred is right. @medstruggle: the duodenal lumen (and the pancreatic /proteases/ you mention) is the site where pancreatic enzymes (“endopeptidases”) cleave large polypeptides into smaller bits. It is at the BRUSH BORDER where the smallest kinds of peptides (dipeptides, tripeptides) are broken down into their amino acids, which finally can be co-transported with Na+ into the intestinal cell. I think about it this way: stomach acid denatures and “opens up” proteins (without any specific cleavage); pancreatic enzymes then cleave denatured polypeptides into smaller bits; brush border enzymes finally break down tiny peptides into absorbable amino acids. +  
welpdedelp  http://1.bp.blogspot.com/-UDdBiBiEgec/UzM61mV4pTI/AAAAAAAABRA/_qCG05fliGk/s1600/VBN.PNG +6  
drdoom  Nice schematic, @welpdedelp +