TBR and EK contradict each other! Where is the truth?

[sillyjoe]

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In TBR Organic Chemistry (even though it is a bio question), Section 6, Passage 5, Question 31, it reads:

Why is amylase released in both saliva and by the pancreas into the small intestine?

A. Salivary amylase is destroyed by the gastric fluids.
B. Pancreatic amylase is weaker than salivary amylase.
C. Salivary amylase is weaker than pancreatic amylase.
D. Pancreatic amylase cleaves amylose with B-linkages while salivary amylase cleaves a-linkages.

Choice A is correct. Amylase breaks down the a-glycosidic linkage. However, it is not stable under highly acidic conditions, where it is readily hydrolyzed. Gastric fluids are highly acidic, so amylase is destroyed in the stomach. It must be released again by the pancreas. This makes choice A the best answer. Both pancreatic and salivary amylase cleave a-glycosidic linkages,so choice D is absolutely wrong. **The two forms of amylase are identical enzymes,so they are equivalent in strength. This eliminates choices B and C.**

EK Bio Chapter 6 reads:

"Like salivary amylase, pancreatic amylase hydrolyzes polysaccharides to disaccharides and trisaccharides; however, pancreatic amylase is much more powerful. Pancreatic amylase degrades nearly all the carbohydrates from the chyme into small glucose polymers, The brush border enzymes finish degrading these polymers to their respective monosaccharides before they are absorbed. "

So EK says salivary amylase is weaker than pancreatic amylase, but TBR says they are the same strength. Which is correct?

 

[Czarcasm]

In TBR Organic Chemistry (even though it is a bio question), Section 6, Passage 5, Question 31, it reads:

Why is amylase released in both saliva and by the pancreas into the small intestine?

A. Salivary amylase is destroyed by the gastric fluids.
B. Pancreatic amylase is weaker than salivary amylase.
C. Salivary amylase is weaker than pancreatic amylase.
D. Pancreatic amylase cleaves amylose with B-linkages while salivary amylase cleaves a-linkages.

Choice A is correct. Amylase breaks down the a-glycosidic linkage. However, it is not stable under highly acidic conditions, where it is readily hydrolyzed. Gastric fluids are highly acidic, so amylase is destroyed in the stomach. It must be released again by the pancreas. This makes choice A the best answer. Both pancreatic and salivary amylase cleave a-glycosidic linkages,so choice D is absolutely wrong. **The two forms of amylase are identical enzymes,so they are equivalent in strength. This eliminates choices B and C.**

EK Bio Chapter 6 reads:

"Like salivary amylase, pancreatic amylase hydrolyzes polysaccharides to disaccharides and trisaccharides; however, pancreatic amylase is much more powerful. Pancreatic amylase degrades nearly all the carbohydrates from the chyme into small glucose polymers, The brush border enzymes finish degrading these polymers to their respective monosaccharides before they are absorbed. "

So EK says salivary amylase is weaker than pancreatic amylase, but TBR says they are the same strength. Which is correct?

Based on the answer choices, it's clear A is the best answer since proteins are broken down in the stomach. Whether or not you want to argue the relative strength of each enzyme is really arbitrary. Some might argue that pancreatic amylase is stronger because it cleaves more often. But if you consider each enzyme carriers out unique enzymatic activites, I don't think it's a valid comparison.

 

[sillyjoe]

Based on the answer choices, it's clear A is the best answer since proteins are broken down in the stomach. Whether or not you want to argue the relative strength of each enzyme is really arbitrary. Some might argue that pancreatic amylase is stronger because it cleaves more often. But if you consider each enzyme carriers out unique enzymatic activites, I don't think it's a valid comparison.

I am asking regardless of the answer since the answer explanation is what directly contradicts EK.

 

[WierdScience]

I am asking regardless of the answer since the answer explanation is what directly contradicts EK.

It is just a mechanism of the concentration that the amylase is released and not the strength of each enzyme per se. The pancreas releases a much more concentrated and directed dose. The salivary gland is just like a warm up.

 

[Czarcasm]

I am asking regardless of the answer since the answer explanation is what directly contradicts EK.

I understand, I'd be curious too. The way I see it though, it seems like a silly comparison and not something likely to be asked on the MCAT. If it's true they have the same enzymatic mechanism, what is also true is that they act on different substrates. If the salivary amylase cleaves glycosidic linkages in a large sugar polymer into a few shorter polymers, that might be considered a priming step that helps the enzymatic activity of pancreatic amylase. Also, like the person above mentioned, concentration is another factor to take into consideration. The environments are also very different since the small intestines is slightly alkaline which means their structures have to be quite different since pH plays an important role on protein structure and activity. There's just too many factors to consider and it's not something I think is worth stressing over, especially since you won't be asked anything about that.

 

[sillyjoe]

It is just a mechanism of the concentration that the amylase is released and not the strength of each enzyme per se. The pancreas releases a much more concentrated and directed dose. The salivary gland is just like a warm up.

Are you sure they are not isozymes and have different kinetics?

 

[WierdScience]

Are you sure they are not isozymes and have different kinetics?

They would have to be isozymes since they function optimally at different pH levels as the previous poster mentioned. And after a cursory search, it seems that pancreatic amylase is more effective even if parotid amylase is at the same concentration. But the pancreas still uses a higher concentration to break down the carbohydrates.

 

[sillyjoe]

They would have to be isozymes since they function optimally at different pH levels as the previous poster mentioned. And after a cursory search, it seems that pancreatic amylase is more effective even if parotid amylase is at the same concentration. But the pancreas still uses a higher concentration to break down the carbohydrates.

Thanks!