Q 17 AND Q7 from B/b AAMC section Bank

br229@georgetown.edu
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Joined: Tue Apr 10, 2018 3:14 pm

Q 17 AND Q7 from B/b AAMC section Bank

Postby br229@georgetown.edu » Wed May 16, 2018 2:15 pm

Q 17. I do not understand the explanation of AAMC. I do know that restriction enzymes cut the dnA at restriction points which are palindromic sequence. But how do we approach this question using this knowledge?

Q7. WHY DO gpcr-- (Germ free have) lower body weight than CONV? (I do understand that if you dont have GPCR (i.e. GPCR--) then you dont have the activation and higher body weight for CONV condition than in normal WT condition. For germ free condition, there is no activation at all because no germs. From this how can we conclude that GF have lower body weight than CONV in GPCR-- CONDITION?
NS_Tutor_Alex
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Joined: Fri Jul 21, 2017 4:11 pm

Re: Q 17 AND Q7 from B/b AAMC section Bank

Postby NS_Tutor_Alex » Sat May 19, 2018 10:33 pm

Hi MCAT_Retaker,

With regards to question 17 from the AAMC biology section bank: This question requires us to draw on our knowledge of Southern Blots. One of those facts is that restriction endonucleases are used to 'cut up' a sample of DNA before it is transferred to an agarose gel to be electrophoresed, allowing the component pieces to be separated by size.

So, that's the content piece that is fairly straight forward and not particularly difficult to memorize. I imagine your next question is something like: "how could I have known to think about this when presented with this question?". This bit is a little trickier but the approach can be used for many many MCAT questions! The trick here is to start with the question of "what is different between the answer choices?". We can see the sequences are different, that's fairly straightforward, but what next? What are those differences is the key. Remembering that the procedure of Southern Blots starts with restriction enzymes (which will be recognizing palindromic sequences) is enough here, because it will land your attention on the only sequence of base pairs that interrupts a palindromic sequence.


With regards to Question 7 from the AAMC biology section bank:

There is a relationship between body weight and GPCR activation that needs to be established in order to correctly approach at least three of the questions in this passage. If we examine figure 1, we can see that GPCR knockouts always have higher body-weights than wild types, regardless of the diet the rats are fed. This might provide some confusion because typically, we think of stimulation of a receptor as causing an increase in 'something'; however, it certainly does not have to. It's crucial that you identify this bias in order to be successful on the MCAT! When we trace the pathway that results in GPCR stimulation, we can see that the rat must eat something with fiber, have the microbiota that express the necessary enzymes for conversion of the fiber into the SFA's, express the receptor for those SFA's and finally, successfully propagate the signal from the receptor into the nucleus. If all goes well, this leads to a lower body weight. The takeaway here is that if any of the aforementioned steps are 'knocked out', then the result is a higher bodyweight. In other words, no bacteria, no signaling molecules in which to stimulate the GPCR's.

Thank you for the questions! Those section banks are pretty tough!

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