May 13, 2016
77
6
Status
Pre-Medical
If you have taken EK FL4 can you please explain the solutions to these questions: 118, 140, 142, 154, 158, 163? I am having trouble interpreting EK's explanations.

118) I picked "tumor suppressor" for this question because the passage says "XRCC3 expression levels are associated with increased DNA repair." Why is this incorrect and what makes the right answer correct?
140) I don't understand this at all. Why is option I correct? Why is the regulatory region even being transcribed?
142) I somehow got this question right, but I can't figure out why and the solution isn't making sense to me.
154) Aren't dendritic cells and B cells both considered Antigen Presenting Cells?
158) Would pyrophosphatase also work on molecules with two phosphates such as ADP?
163) The solutions say eliminate answer C, but then later picks C as the correct answer. Why is C the correct answer?
 

theonlytycrane

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Mar 23, 2014
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If you have taken EK FL4 can you please explain the solutions to these questions: 118, 140, 142, 154, 158, 163? I am having trouble interpreting EK's explanations.

118) I picked "tumor suppressor" for this question because the passage says "XRCC3 expression levels are associated with increased DNA repair." Why is this incorrect and what makes the right answer correct?
I missed this one too and also picked tumor suppressor. The supporting sentence is above in that paragraph "Overexpression of genes involved in double-strand break repair was associated with an increased tendency to generate highly invasive cancer cells." This means that the y-axis on the graphs below (invasiveness) mean cancerous. It's just kind of confusing in the way it's presented. Apparently too many DNA repair enzymes cause cancer!

140) I don't understand this at all. Why is option I correct? Why is the regulatory region even being transcribed?
I think they mean transcription of the gene downstream of the regulatory region. So the regulatory region gets wonked, therefore the downstream gene may be transcribed less.

142) I somehow got this question right, but I can't figure out why and the solution isn't making sense to me.
Figure 2 shows apoptosis of cells after radiation. Starting from the left, the WT shows that cells that get radiated undergo a lot of apoptosis. But then they knock out either mnk or dp53 and in both cases the cells no longer undergo apoptosis! mnk and dp53 must have something to do with helping the cells to die. This goes with choice (C). mnk and dp53 probably help detect some DNA damage and then tell the cell "oh **** we're done for! It's time to die!!!". The other options would keep the cell alive, which would mean the cell would probably die more if mnk or dp53 were knocked out in these cases.

154) Aren't dendritic cells and B cells both considered Antigen Presenting Cells?
I thought of B-cells as anti-body makers. The immune system is complex so they could likely present antigens too. But I went with (A) since the main job of a dendritic cell is to be an antigen presenting cell.

158) Would pyrophosphatase also work on molecules with two phosphates such as ADP?
Maybe, but then we would be left with a nucleoside that needs more phosphates later.

163) The solutions say eliminate answer C, but then later picks C as the correct answer. Why is C the correct answer?
It's a typo in the solutions. They meant that to say "eliminate answer B". This is a super value judgement question, though. There's nothing in the passage talking about the enzyme's active site so it's just EK's opinion on which one is more "correct". I went with A for reference because at least that agrees with background knowledge from biology. Whether Pro is or isn't part of the enzyme active site is unknown and not discussed.
 
OP
K
May 13, 2016
77
6
Status
Pre-Medical
Apparently too many DNA repair enzymes cause cancer!
Mind = blown

I think they mean transcription of the gene downstream of the regulatory region. So the regulatory region gets wonked, therefore the downstream gene may be transcribed less.
Okay awesome. Can you also explain what makes II and III correct?

I thought of B-cells as anti-body makers. The immune system is complex so they could likely present antigens too. But I went with (A) since the main job of a dendritic cell is to be an antigen presenting cell.
That's really odd. I just checked with my bio textbook and it says B cells are antigen presenting cells too. But like you mentioned the main job of a dendritic cell is to be an APC so that's probably a better answer.
 

theonlytycrane

5+ Year Member
Mar 23, 2014
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1,687
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Medical Student
Okay awesome. Can you also explain what makes II and III correct?
If the regulatory region of a DNA segment gets messed up, it could be possible that downstream transcription gets inhibited as well as local transcription on that same chromosome. Maybe the gene coded for some transcription factor influencing the transcription of another gene close by. Using the same logic, the transcription factor could also influence transcription on another chromosome, so lack of that factor could inhibit transcription in III as well. These kind of require a lot of imagination- I wish they were more clear at times.

That's really odd. I just checked with my bio textbook and it says B cells are antigen presenting cells too. But like you mentioned the main job of a dendritic cell is to be an APC so that's probably a better answer.
Yeah hopefully AAMC wouldn't have us make that call and instead make the other answer choices more clearly wrong. It's good review for us to consider B-cell and dendritic cells here though.
 
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