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AAMC COVID-19 FLE-7 Chem Question 4
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Hanna_3759
#1 Posted : Thursday, July 09, 2020 5:11:58 AM
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The solution text for this question says that catalytic efficiency can be interpreted using only Kcat. It also says that specificity constant = Kcat/Km. I have learned from U World MCAT prep that Catalytic Efficiency = Kcat/Km. Which is correct?
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INSTR_Katerina_102
#2 Posted : Monday, July 13, 2020 5:02:14 PM
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Hi Hanna,

To the best of my knowledge and memory, I would say kcat/Km is the specificity constant. Catalytic efficiency should depend primarily on kcat, as Km only dictates the propensity of enzymes to bind to substrates (and does not dictate catalysis itself).

I hope this helps!
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Hanna_3759
#3 Posted : Monday, July 13, 2020 8:48:02 PM
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Hi katerina,

I've checked with KhanAcademyMedicine and it actually says that catalytic efficiency is Kcat/Km [at this link at 6:35: https://www.khanacademy....chaelis-menten-equation]. I assume this is trustworthy in terms of MCAT knowledge since it is funded by the aamc.

So then what is a specificity constant? And going back to the Altius question, it must be wrong then?
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INSTR_Katerina_102
#4 Posted : Monday, July 13, 2020 9:47:07 PM
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Hi Hanna,

I can't speak to the accuracy of Khan academy because I've never used it as an MCAT resource myself but from primary literature sources I see that Kcat/Km seems to be defined as specificity constant distinct from catalytic efficiency.

https://www.cell.com/tre...ogy/fulltext/S0167-7799(07)00085-6

https://www.tandfonline..../02648725.2010.10648157

Looking further though, I see some other literature sources defining catalytic efficiency as Kcat/Km.

I think this comes from the fact that they seem to be used interchangeably in literature, so you should be safe treating both terms interchangeably.

I'm sorry I can't provide a more satisfactory answer than this, I hope it is somewhat helpful but perhaps another instructor will weigh in with more concrete information.


Katt
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