Can someone walk me through the AAMC 11 Ebola graph please

[TX500]

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This graph confused the hell out of me 🙁

Specifically, all of the damn +/- -/- +/+ !

I think my BIGGEST issue is that I don't know how to approach these kinds of passages. Do you guys take notes while trying to figure out what's going on? There's so much unfamiliar terminology!

 

[Jepstein30]

This graph confused the hell out of me 🙁

Specifically, all of the damn +/- -/- +/+ !

Can you post the text along with it? I didn't find this passage that difficult (bio major, so lots of experience with this kind of stuff) but don't remember it enough to explain anything.

If you can't, I'll log onto e-mcat later and see if I still have access.

 

[TX500]

Can you post the text along with it? I didn't find this passage that difficult (bio major, so lots of experience with this kind of stuff) but don't remember it enough to explain anything.

If you can't, I'll log onto e-mcat later and see if I still have access.

Sure thing. Bottom part got cut off, but the graph is also at the top. Thanks again buddy 🙂

 

[BryanNextStep]

I was just working through this passage last night with one of my tutoring students. It's a trainwreck - by far one of the most confusing passages in all the AAMC tests.

So the basic idea they're trying to convey with that graph is that the virus NEEDS the host cell to have both CatB AND CatL in order to infect it. (If I'm remembering correctly) there's some stuff on the surface of the virus that the virus expects the host to cleave with the proteases CatB and CatL. That cleaving then lets the virus get in and infect.

So what did the experiment do? They took some mouse cells and genetically engineered them.

The first (white) bar is the wild type (WT). They have the normal genes - they are both CatB and CatL positive. The virus easily infected those cells.

Next, they had a mouse cell line that was a mutant b/c it did NOT produce CatB. The (-) there is meant to show that the line is (I think) homozygous recessive for NOT having the CatB gene. The researchers then artificially introduced a number of other genes.

Notice that when the CatB -/- cell line got CatL introduced, you got almost no infection. Tiny little bar graph. That's because the virus needs BOTH to infect. So then when they introduced CatB, the bar graph was huge. The cell naturally has CatL; the +/+ is meant to show you that the cell is wild-type for CatL - it produces normal amounts of it. Then when we artifically introduce CatB, the virus has what it needs and we get a huge bar graph showing lots of infection.

Now the last cell line - it is engineered to have NEITHER the CatB nor the CatL proteins naturally. Hence the -/- for both of those genes. What happens? The virus can't infect! When we artificially introduce CatL or CatB by themselves, we get a little bit of infection, but it's not until we artificially introduce BOTH CatL and CatB back into the cell that the virus can infect.

Hope this helps! 🙂

 

[ur2l8]

Look up what double knockouts are with regard to lab mice

 

[Gauss44]

http://forums.studentdoctor.net/showthread.php?t=905004

http://forums.studentdoctor.net/showthread.php?t=849057

Kaplan: http://syllabus.kaptest.com/studenthome/syllabus/assignment/Kaplan_Explanations_AAMC_Test11.pdf

 

[TX500]

Thanks for all of your responses!

Does that mean a +/- is + for one allele on a homologous chromosome and is - for the other allele on the other homologous chromosome? i.e. heterozygous?

 

[Jepstein30]

Thanks for all of your responses!

Does that mean a +/- is + for one allele on a homologous chromosome and is - for the other allele on the other homologous chromosome? i.e. heterozygous?

Yes, which isn't asked about because it's irrelevant. They could have thrown it in if they gave you information on the dominance of the two alleles though.

 

[TX500]

Yes, which isn't asked about because it's irrelevant. They could have thrown it in if they gave you information on the dominance of the two alleles though.

Awesome, I think I finally understand now! Thanks everyone!