Hello
Can someone explain me why the answer is C for the question 25? AAMC answer do not sound convincing to me
Qn: WHICH STATEMENT IS SUPPORTED BY THE DATA SHOWN IN FIGURE 1?
A) STRA 5 ACTIVITY IS ASSOCIATED WITH THE CRBP-I INTRACELLULAR PROTEIN, BUT NOT THE LRAT INTRACELLULAR PROTEIN
B) STRA 6- MEDIATED RETINOL UPTAKE IN CELLS IS ONLY DEPENDENT ON THE ABILITY TO BIND RETINOL.
C) NEITHER LRAT NOR CRBP 1 ARE ABSOLUTELY REQUIRED FOR INTRACELLULAR RETINOL UPTAKE.
D) RELEASE OF RETINOL FROM HOLO-RBP IS MOST EFFECTIVE IN THE STRA 6 ONLY CONDITION
Pet peeve: Before I begin, please be sure to identify what is the source of these questions. The AAMC has the Question Packs, composed from retired old MCAT exams based on the 45 point test, and the separate Section Bank, which is entirely devoted to the new MCAT. Your question is from the Section Bank; the title of this thread is "question bank" which is nonexistent. Not to be nitpicky, it just helps labeling correctly!
Excellent question. For this, let's look at the figure (you'll have to log into your AAMC account for that - I don't want to post it here or the passage because it breaks the ToS).
Let's look at the figure 1. According to figure 1, we see the x-axis, the independent variable, is time, recorded in minutes, while the y axis, or dependent variable, is the relative retinol uptake activity.
First and foremost, what is the figure even pointing out? As time goes on, we seem to be measuring the uptake of this retinol substance.
Now that we've established what the figure is presenting us with, let's look at the four lines on the figure. I'm going to work my way from the bottom to the top.
Control Line:
As time increases, from t = 0 to t = 180, we see a very tiny increase at the start of the experiment, approximately 15 minutes in or so. We see this relative retinol uptake activity to rise minimally from t = 15 to t = 180. The max value of the relative retinol uptake activity is approximately 5 or so.
STRA6 Line:
Again, start at t = 0. Here we see a slightly greater relative retinol uptake activity, however, it is
larger than the control line. We see this relative retinol uptake activity to be roughly 10?
STRA6/CRBP-1 Line:
We see a dramatic increase in relative retinol uptake activity compared to the control and STRA6 line. We wee it roughly level off at a value of 30.
STRA6/LRAT Line:
The final line! We see this line dominates all the other lines; it has the largest initial slope and peaks with the maximal relative retinol uptake activity at every time increment recorded when compared to the other values.
Now, back to the question: Which statement is supported by the data shown in Figure 1?
A. STRA6 activity is associated with the CRBP-I intracellular protein, but not the LRAT intracellular protein.
A is FALSE. Look at the lines in question. Answer choice A states that the STRA6 activity is impacted by the CRBP-I protein, but not the LRAT protein. If that were the case, then those two lines should be the same. However, they are not! Notice how much more relative retinol uptake activity the STRA6/LRAT line has compared to the STRA6/CRBP-I line!
B. STRA6-mediated retinol uptake in cells is only dependent on the ability to bind retinol
B is FALSE. If that were the case, all the lines should be the same as the control. STRA6, STRA6/CRBP-1, and STRA6/LRAT should all be the same if the relative retinol uptake activity is based purely on the ability to bind retinol.
C. Neither LRAT nor CRBP-I are absolutely required for intracellular retinol uptake.
C is TRUE! Look at the answer choice very carefully. The words "absolutely required" are important here. Choice C is arguing that neither LRAT nor CRBP-I are ABSOLUTELY NECESSARY for retinol uptake. That means that without LRAT or CRBP-I, we should have
some relative retinol uptake activity. What line can show this? The STRA6 line by itself. Notice how the STRA6 line is, albeit slightly, greater than the control line. Based on this, we can state that really STRA6 can uptake retinol. Not by much, but we don't quite necessarily require the assistance of CRBP-1 or LRAT.
D. Release of retinol from holo-RBP is most effective in the STRA6 only condition.
D is FALSE. If this were the case, wouldn't we observe the STRA6 line to have the maximal values for the retinol uptake? That's clearly indicated via the STRA6/LRAT conditions, and not STRA6 alone.
Hope this helped - inbox me with other questions or this same one if you didn't quite grasp it.
