digestion

[unDRdog]

ok..i cant figure this one out...this is a question out of an ole school Kaplan bio book... maybe some of you have seen it:

"In an experiment, enterokinase secretion was blocked. As a direct result, secretion of all of the following enzmes was affected EXCEPT;
A. trypsin
B. aminopeptidase
C. chymotrypsin
D. carboxypeptidase

Answer is B...i understand its not A and C but how do you know its B and not D???? i cant figure this one out...am i just flat out missing the info?

---

Members don't see this ad.

 

[Baboo Bhaiya]

ok..i cant figure this one out...this is a question out of an ole school Kaplan bio book... maybe some of you have seen it:

"In an experiment, enterokinase secretion was blocked. As a direct result, secretion of all of the following enzmes was affected EXCEPT;
A. trypsin
B. aminopeptidase
C. chymotrypsin
D. carboxypeptidase

Answer is B...i understand its not A and C but how do you know its B and not D???? i cant figure this one out...am i just flat out missing the info?

There are 3 places that protein digestion takes place:

1. Stomach - important proteolytic enzyme here is Pepsin

2. Duodenum and Jejunum (small intestine) - the important proteolytic enzymes here are enzymes of the pancreatic secretions (Trypsin, Chymotrypsin, and Carboxypeptidase)

3. Brush Border (Microvilli) of the Small Intestine - two important proteolytic enzymes here are the aminopeptidase and dipeptidases

Since enterokinase is also a brush border enzyme, they may be implying that aminopeptidase secretion would be affected

Although I doubt that such a question would appear on the MCAT...

I understand how enterokinase secretion (which is part of brush border) will have no effect on trypsin, chymotrypsin, and carboxypeptidase secretion (since they are pancreatic secretions) but how does it make the fourth choice true.

How will blocking enterokinase secretion affect aminopeptidase secretion?

 

[Cjc555777]

so i'm not entirely sure but I do have an educated guess. Enterokinase is a serine protease. So my guess is that aminopeptidase doesn't have any serines in it (at least any that can be cleaved). Don't worry about it because that's something that's way too specific. My other guess is that we would have to think about which specific organic reactions this could apply to and it may have to do with the pathway, but nothing comes to mind. Don't worry about it too much

 

[Charles_Carmichael]

Enterokinase and aminopeptidase are found in the brush border of the intestinal epithelia. Enterokinase is important because it activates trypsin (by cleaving trypsinogen). Trypsin activates all the other pancreatic proenzymes; so without active trypsin, the pancreatic enzymes would not the activated.

Blocking enterokinase activity may affect pancreatic enzyme secretion by causing increased secretion of pancreatic enzymes. It would be like negative feedback since the chyme that enters the duodenum stimulates the pancreatic/bile secretions. If the contents of chyme are not digested, they can continue to stimulate more secretion.

For example, in response to lipids and peptides, the I cells secrete CCK, which stimulates the secretion of enzymes from the acinar cells in pancreatic ducts. If these enzymes are not activated, the lipids and peptides will not be digested. Their continued presence stimulates more CCK secretion and thus, more enzyme secretion from the pancreas.

Hope this helps.

Edit: To answer your question, aminopeptidase secretion will NOT be affected because it's not a pancreatic enzyme. Trypsin, chymotrypsin, and carboxypeptidase are all pancreatic enzymes, and pancreatic enzyme secretion WILL be affected if the enzymes are not activated because of the continued presence of nondigested material. Their secretion will be affected just like I described in my above explanation.