AAMC 11 Bio Qs

[Joker88]

sorry guys, i have been posting a lot of questions lately. Definitely wanted to clarify some things on the bio section for aamc 11. There were some convoluted ones in this section so please help out if you can:

110. Which of the following best describes the bond that would form between the following two nucleotides if they were located adjacent to each other as shown in a single strange of DNA?

D. A bond between the phophateof the adenine and the sugar of the thymine.

Solution: The question shows two adjacent nucleotides and asks the examinee to predict the most likely bond that would form between them. As oriented, the most likely would be between the phosphate of the bottom nucleotide (adenine) and the sugar of the top nucleotide (thymine). This is the familar bonding pattern that makes up the backbone of the DNA, alternation sugar and phosphate groups joined by the ester bonds.

How did they know it was adenine to thymine? Just based off their general locations? Since adenine was on bottom it is more like the bind its phophate group to the sugar on the thymine?

135. Based on the passage, is CatL expression sufficient for the VSV-EGP infection of the mouse cell lines presented in figure 1?

C. No, because VSV-EGP does not infect the CatB -/- cells expression CatL better than it infects the CatB -/- cells not expressing CatlL.

136. Based on the passage, does optimal VSV-EGP infection in vitro require CatB, CatL, or both? Optimal infection:

C. Requires both CatB and CatL

--I got 135 correct and 136 wrong. I feel like these answers contradict themselves? If CatL with CatB in 135 is not as expressive as CatB alone how does optimal infection require both?

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[tn4596]

for ur first question, since it is a discrete question i can answer it, you should know that a bond between nucleotides in nucleic acid is from the 3' OH group to the 5' Phosphate group. It is just something you have to know.

 

[Joker88]

for ur first question, since it is a discrete question i can answer it, you should know that a bond between nucleotides in nucleic acid is from the 3' OH group to the 5' Phosphate group. It is just something you have to know.

They had the phosphate group from the 3' adenine binding to the sugar base of the 5' thymine though

 

[Joker88]

can anyone whos done aamc 11 help me with these ?

 

[MT Headed]

110. Which of the following best describes the bond that would form between the following two nucleotides if they were located adjacent to each other as shown in a single strange of DNA?

The key here is that they told you the Thymine is 5' and the Adenine is 3'. Nucleic acids are built 5->3. It's the 3' nucleotide that donates two extra phosphates for the energy to add it to the growing chain, and uses its third phosphate to connect to the previous sugar. So the answer is the sugar of the thymine connects to the phosphate of the adenine.

 

[MT Headed]

135. Based on the passage, is CatL expression sufficient for the VSV-EGP infection of the mouse cell lines presented in figure 1?

C. No, because VSV-EGP does not infect the CatB -/- cells expression CatL better than it infects the CatB -/- cells not expressing CatlL.

In questions like this, I like to figure out if the answer is yes or no first. Then I can eliminate half the answers. By reading the graph columns 5 and 7, you should be able to determine that adding CatL makes no difference. Therefore CatL is not sufficient. Therefore you can eliminate A and B.

So, what's the best reason that CatL is not sufficient? Well, answer D compares (B+L) to (B only). That might determine necessity, but it doesn't determine sufficiency.

Answer C compares (L only) with (nothing). And clearly adding just (L) by itself didn't accomplish anything. This is a good demonstration that L is not sufficient all by itself.

 

[MT Headed]

136. Based on the passage, does optimal VSV-EGP infection in vitro require CatB, CatL, or both? Optimal infection:

C. Requires both CatB and CatL

The table's highest columns are the ones where both CatB and CatL are present, either because it is wildtype, or because some of the genes were removed and re-added. Optimal infection requires both.

I'm not sure why you think question 135 implies that (CatB) is more effective than (CatB+CatL). The data in the graph doesn't suggest this. Maybe you think that because answer 135D is wrong, answer 135D must also be false? 135D is a case of a statement that is certainly true, but doesn't answer question 135.


I seriously spent 20 minutes on this passage. It is more of a test of verbal skill and logical thinking than it is of biological sciences. I'm glad I didn't get a passage like this on my real MCAT. If you want more practice with passages in this style, I recommend getting the Official Guide to the MCAT Exam. There are several more in that book just like this one.

 

[Joker88]

yeah this is definitely a tuff one but I think I get what youre saying now. It was more about figuring out what they were asking for. They were pretty tricky. THanks for the help MT!

 

[justhanging]

Whats the point of introducing genes into cells that already have them? If the culture genotype is CatL+/+ whats the point of introducing the gene CatL? Just seems redundant.

This confused me alot in the passage but once I got it, and it took me a while, it all made sense.

 

[drechie]

can anyone tell me what the "bacteria" columns actually mean?


the graph is at this link: http://biology.stackexchange.com/qu...ding-introduced-genes-and-virus-infected-cell

 

[NextStepTutor_3]

Hi @drechie ! I know this is an old-ish question, but the passage is so great it's worth answering. The "bacterial" genes are just meant to serve as control groups for the two cell lines - in other words, to show us what happens when we don't introduce any genes of interest. CatB and CatL are mammalian proteases, so introducing bacterial genes presumably should have no effect. They're really meant as standards of comparison for cases such as the fourth bar from the left (in which we introduced CatL to a cell line that already expressed Cat L, but not CatB). We can see that simply introducing CatL to that line doesn't increase infectivity any more than introducing "random," unrelated bacterial genes, and thus must be ineffective. The same thing could have been accomplished by replacing the "bacterial" bars with bars in which no genes were introduced at all, but this method is preferable because 1) it looks more confusing to the test-taker and 2) it means that each trial at least involved the same transfection process, which helps control the overall experiment. (In other words, transfecting genes that don't do anything is as similar to the "real" transfection conditions as possible, making it better than not transfecting anything at all.)