Saturday, June 16, 2007
Cellular Respiration Ninja Enzymes
Here's a student video presentation of glycolysis and respiration. It's much better than most [e.g., An Example of High School Biochemistry]. However, there are two errors in the video. The first one is fairly serious. The second one is less serious but it's something we cover in my class and it helps illustrate a fundamental concept about how certain reactions work. The second error was very common in most biochemistry textbooks in the past but it's been eliminated from the majority of 21st century textbooks. Can you spot both errors?
[Hat Tip: Greg Laden]
[Hint: What are the products produced by glycolysis and by the Krebs cycle?]
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6 comments :
First of all, thanks for the comments and the link! I appreciate it.
I think (as the creator of this video) that there are quite a few errors: The mitochondrion isn't shown to have a double-membrane. The products of the Krebs cycle should really be multiplied by 2 to account for the 2 pyruvates produced. Also, the production of NADH and FADH2 from NAD and FAD don't just involve electrons jumping into their arms, but require the addition of hydrogens -this way emphasizes their role as "electron carriers".
There are probably other things I missed too. I just hoped to be able to provide a simple model sufficient for the understanding required by an AP Biology student. I'd like to hear the errors I made actually are. Thanks.
-Chris Allison
Now that I think about it, I should have shown all the CO2 produced in the Krebs cycle. It is rather important, so that's a pretty big omission. I'm still not sure what exactly the other error is though.
Thanks again,
Chris
In the glycolysis section, the correct products are 2 ATP and not 4 ATP. While it's true there are 4 ATP molecules produced, there are also 2 ATPs used up in the hexose stage. Thus, the net gain is 2 ATP per glucose.
In the citric acid cycle the correct product is QH2 and not FADH2. FADH2 remains bound to the enzyme (succinate dehydrogenase or succinate:ubiquinone oxidoreuctase) and the reaction isn't complete until the electrons are passed to quinone (Q) to make QH2.
It was common in past years to consider FADH2 as a product but this is incorrect [see Brown ,2000].
Ok. As a high school science teacher I hate teaching inaccuracies/incorrect facts, theories etc [but I'm sure I do it]. I'm sure it happens a lot! So, how high is the QH2 vs FADH2 in terms of high school relevancy? Once again, this is an excellent example of how subtle important changes may not filter down to high school for years. Also, I'm not convinced the AP college board or IBO would acknowledge QH2 as an acceptable answer. Everyone teachers FADH2.
Your opinions please?
Linzel says,
So, how high is the QH2 vs FADH2 in terms of high school relevancy? Once again, this is an excellent example of how subtle important changes may not filter down to high school for years. Also, I'm not convinced the AP college board or IBO would acknowledge QH2 as an acceptable answer. Everyone teachers FADH2.
It's as accurate to say that FADH2 s the product of the succinate dehydrogenase reaction as it would be to say that it's the product of the pyruvate dehydrogenase reaction. In other words, it's wrong.
High school teachers must find it frustrating when they have to teach incorrect facts because the AP college board expects a wrong answer on their tests. I imagine the same problem applies to the SAT's.
We have similar problems in university. Some of the material I teach in my course directly conflicts with material taught in other science courses. My students have to learn to give one answer on my exams and a completely different answer on the exam in another course. All I can do is point out the differences and explain why I think one answer is right and another is wrong.
If one thing came out of Dr. Moran's course, it was the FADH2/QH2 change, that's for sure. I must admit that it's just better to use QH2 instead anyway. Makes more sense to me.
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