AAMC Sample test C/P Q38, Q46

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AAMC Sample test C/P Q38, Q46

Post by dbflsdl0228 » Mon Nov 05, 2018 10:35 am

Good morning! Hope anyone could help me out for these two questions! I am really struggling and couldn't understand AAMC explanation.

Q38. How do we keep tracking of 14-C labeled during these reaction? Could you please explain in different ways? I always spend a lot of time at this kind of question because I am so weak at this.

Q46. Could you also explain what equation we have to know in order to solve this question? I am not still sure about why the correct answer is A.

Thank you so much!
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Re: AAMC Sample test C/P Q38, Q46

Post by NS_Tutor_Will » Wed Nov 07, 2018 9:34 am

Q38 is a little tough to explain in writing, but I'll try my best. We need to follow the 14-C carbons on the acetyl-CoA molecules. Reaction 1 gives us the first two and they don't change after that reaction (positions 2 and 4). In the second reaction, acetyl-CoA attacks the carbonyl to the left of acetoacetyl-CoA. The steps of that reaction aren't too important, but we end up with another 14-C next to the old carbonyl (position 5). The decarboxylation is the final step, but it doesn't involved the 14-C labeled positions.

For Q51, you need to understand Archimedes' principle. The AAMC summarizes it this way:
The ratio of the density of an object to the density of the fluid it is submersed in is equal to the ratio of the weight of the object in air to the difference of submersed weight and weight in air
So, the equation: ρobj / ρfluid = weight(obj) / (weight(obj) - weight(sub))

For fluids, I find it helpful to watch videos explaining the concepts because, at least for me, they are often counter intuitive and difficult to visualize. I'd suggest watching some of those and following along conceptually rather than focusing on just the equations which are often pretty confusing!
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Re: AAMC Sample test C/P Q38, Q46

Post by Karolina » Mon Dec 31, 2018 12:11 am

Regarding the quote you posted (the AAMC explanation to the question)- how do we arrive at that equation? I've tried deriving it and have been having no luck and I can't find that anywhere online!
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Re: AAMC Sample test C/P Q38, Q46

Post by NS_Tutor_Will » Mon Dec 31, 2018 1:00 pm

I'll try to derive it here from a few other fluids formulas, but the notation is a little tricky with the forum formatting!

Start with two equations:

Wwater = Wair - Fbuoyant (weight in water equals weight in air minus the buoyant force)
Wair = Fg = mg (weight in air equals the force of gravity equals mass times gravitational acceleration)

Then work with the first equation to get:

Wair - Wwater = Fbuoyant
Wair-Wwater = density(water) * Vol(submerged) * g

Then we can use that derivation along with the second equation from above:

Wair-Wwater = density(water) * Vol(human) * g

(Wair)/(Wair-Wwater) = (mg)/(density(water) * Vol(human) * g)

...which simplifies to...

(Wair)/(Wair-Wwater) = mass(human) / Vol(human)

Note that we can cancel the density of water because it is taken to be one (1 g/cm^3).

That final equation states that Density(human) = Wair / Wair-Wwater

I hope this helps!
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