[ALD]

I had a frustrating conversation with my Microbiology instructor about one of these problems after receiving the graded test. We differ on the correct answer. I would like to get some feedback first and then I will post what each of us thought was the correct answer. Thanks in advance for any help.

[JGK]

Based on the forum rules you need to show your work first in order that we do not do your work for you.

[ALD]

Based on the forum rules you need to show your work first in order that we do not do your work for you.

I didn't want to give my answers until after feedback, but I will if those are the rules. I thought this was a very basic question. Here is my thought process:

This is a redox reaction. The NAD+ is being reduced to NADH. At the end of the reaction, NADH is left and it is in its reduced state. For #14, I answered d.

The reaction that it is coupled to is isocitric acid to ketoglutaric acid. This is an oxidation reaction. Therefore, at the end of the reaction ketoglutaric acid is left and it is in an oxidized state relative to what it started as. For #15, I answered b.

Any thoughts?

[Wreath]

Well, I'm not very good english speaker, so I'm not sure if I understood the question correctly. But, I'd say, that there are basicly two couples showing red/ox state: NADH/NAD+ and Isocitrate/Ketoglutarate. So, from that, I would assume correct question for 14 should be e), because both NADH and Isocitrate are reduced forms/states. Then in 15, there are two correct answers, b) and c).
But again said, I'm not sure I understood correctly.

[ALD]

Well, I'm not very good english speaker, so I'm not sure if I understood the question correctly. But, I'd say, that there are basicly two couples showing red/ox state: NADH/NAD+ and Isocitrate/Ketoglutarate. So, from that, I would assume correct question for 14 should be e), because both NADH and Isocitrate are reduced forms/states. Then in 15, there are two correct answers, b) and c).
But again said, I'm not sure I understood correctly.

That makes sense. However, the question states "at the end of the reaction". Doesn't that exclude reactants?

My answer on #14 was d and that was deemed the correct answer by the instructor. My instructor said e was the answer for #15. That makes absolutely NO sense to me.

[Wreath]

well, so ask him for an explanation, because it makes no sense for me either. the only possibility for me is the CO₂ missing in equation, but I have no idea how it should be working. In my opinion, at the end of reaction is ketoglutarate the one which is oxidized...but maybe someone gives us the explanation..

[ALD]

well, so ask him for an explanation, because it makes no sense for me either. the only possibility for me is the CO₂ missing in equation, but I have no idea how it should be working. In my opinion, at the end of reaction is ketoglutarate the one which is oxidized...but maybe someone gives us the explanation..

I did ask her. She said because isocitric acid supplied the electrons for NAD+ to be reduced that means that isocitric acid is in an oxidized state at the end of the reaction. I said that first of all, isocitric acid isn't even around at the end of the reaction. It is converted to ketoglutaric acid. Second, isocitric acid is in a relatively reduced state (compared to ketoglutaric acid).

Am I right?

[Wreath]

as far as I know, this is the reaction of isocitrate dehydrogenase, which is, quoting wikipedia, "the oxidative decarboxylation of isocitrate, producing alpha-ketoglutarate (α-ketoglutarate) and CO2 while converting NAD+ to NADH. This is a two-step process, which involves oxidation of isocitrate (a secondary alcohol) to oxalosuccinate (a ketone), followed by the decarboxylation of the carboxyl group beta to the ketone, forming alpha-ketoglutarate."

so: 1) we are missing something important or 2) your teacher is wrong..

[Yggdrasil]

I think that you clearly understand what's going on in the reaction and the teacher's answers do not make sense.  Yes, isocitric acid acts as a reducing agent in the reaction, but in the reaction it gets oxidized to α-ketoglutaric acid.  Her answer would make sense if the question had asked "Which compound acts as the reducing agent?" or "which compound gets oxidized?" but the answer and explanation do not make sense as the question is currently worded.  She says that "isocitric acid is in an oxidized state at the end of the reaction" but the oxidized state of isocitric acid in this reaction is α-ketoglutaric acid!  This logic behind the response also seems inconsistent with the answer to the previous question.

This is why biologists should not be allowed to teach chemistry...

[JGK]

Based on the forum rules you need to show your work first in order that we do not do your work for you.

I didn't want to give my answers until after feedback, but I will if those are the rules. I thought this was a very basic question. Here is my thought process:

This is a redox reaction. The NAD+ is being reduced to NADH. At the end of the reaction, NADH is left and it is in its reduced state. For #14, I answered d.

The reaction that it is coupled to is isocitric acid to ketoglutaric acid. This is an oxidation reaction. Therefore, at the end of the reaction ketoglutaric acid is left and it is in an oxidized state relative to what it started as. For #15, I answered b.

Any thoughts?

I agree with your answers for both questions (but with a degree in biochemistry, what do I know about it  )

[ALD]

I appreciate all the responses. This was not the first issue like this that I have had. In fact, there have been multiple issues. On this particular issue, she said "You are a chemist. You should know this." I said "I understand it very well." She then said "I don't care what you say. I'm not giving you a point." I reply, "I don't care if you give me a point or not. It doesn't make your answer correct."

Oh well. I'm not sure if it's worth my effort to push the issue. I just hate it when incorrect information is propagated.

Funny story:
One time in class, the discussion was about UV radiation damaging DNA. She said "this is why tanning beds now use IR radiation". I couldn't keep my mouth shut. I politely said, "Ummm, I'm pretty sure tanning beds use UV radiation--and UVA radiation at that." She replies "are you sure?". I said "yeah, I'm pretty sure."

People want a tan--not to be baked.

[AhmedEzatAlzawalaty]

for me , at the end of the reaction, NADH is the reduced compound,thi is d for 14
and e for 15.becoz at the end of the reaction there is only ketoglutaric acid and NADH but isocitric acid has been consumed and there is not more of it anymore.