EK Bio In-Class Exams #120

[dougkaye]

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120. Pancreatic enzymes are released from the pancreas in an inactive form called a zymogen. Which of the following activates the zymogen form of pancreatic lipase.

A. bile salts
B. trypsin ("correct" answer)
C. low pH
D. high pH

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I can't find a single source that supports this answer. I've never heard of trypsin activating a zymogen other than proteolytic ones. Most of my sources say that pancreatic lipase is secreted in active form, and I found one source (dubious b/c not a textbook) that says pancreatic lipase is activated by bile salts. Curious if anyone had an idea. I chose "Low pH" because acid chyme is low pH until it's neutralized by HCO3-, but bile salts could have worked also as a guess.

From wiki (sorry, couldn't fit a better source🙂 Unlike some pancreatic enzymes like trypsin which are first secreted in the inactive form (e.g. trypsinogen), pancreatic lipase is secreted as the active enzyme.

 

[shffl]

120. Pancreatic enzymes are released from the pancreas in an inactive form called a zymogen. Which of the following activates the zymogen form of pancreatic lipase.

A. bile salts
B. trypsin ("correct" answer)
C. low pH
D. high pH

---
I can't find a single source that supports this answer. I've never heard of trypsin activating a zymogen other than proteolytic ones. Most of my sources say that pancreatic lipase is secreted in active form, and I found one source (dubious b/c not a textbook) that says pancreatic lipase is activated by bile salts. Curious if anyone had an idea. I chose "Low pH" because acid chyme is low pH until it's neutralized by HCO3-, but bile salts could have worked also as a guess.

From wiki (sorry, couldn't fit a better source🙂 Unlike some pancreatic enzymes like trypsin which are first secreted in the inactive form (e.g. trypsinogen), pancreatic lipase is secreted as the active enzyme.

Weird question. But I would have arrived at B with process of elimination. Zymogen form requires the protein to be cleaved to be activated. Bile salt and pH levels do not cleave proteins but trypsin, on the other hand, does.

 

[dougkaye]

But by process of elimination pH is a good answer as well. Many proteins are activated or inactivated based on pH changes. A good example is lysozomal enzymes which only function at low pH levels so that they don't "digest" the cell. I agree with you that trypsin "seems like" a good answer because it is a peptide that activates other digestive zymogens via cleavage. But I'm trying to determine if EK's answer is factually correct.

 

[shffl]

But by process of elimination pH is a good answer as well. Many proteins are activated or inactivated based on pH changes. A good example is lysozomal enzymes which only function at low pH levels so that they don't "digest" the cell. I agree with you that trypsin "seems like" a good answer because it is a peptide that activates other digestive zymogens via cleavage. But I'm trying to determine if EK's answer is factually correct.

I agree with you that pH can be a possible answer as well. But the best one that jumps right out for me was trypsin. Not sure about whether EK's answer is factually correct or not though. I just know a lot of their solutions lead to frustrations for me.

 

[soby10]

I agree with you this question doesn't make any sense to me either. Trypsin activates all pancreatic proteases not lipases. Pancreatic enzymes are in their zymogen form because this prevents digestion of the pancreatic cells. The only logical answer would be high PH but lipase isn't in a zymogen form so it doesn't have to be activated. The bile salts answer doesn't seem like a activator but more like a co-regulator of fat digestion. If this question is from EK it may be an error their known to have a few.

 

[dougkaye]

K thanks for the ideas. I think the important thing is to understand zymogens and some of the key zymogens that are activated, and by which enzymes. I doubt the MCAT will test this in such an ambiguous manner.