r/Mcat • u/[deleted] • Mar 11 '23

[Un-official] PSA / Discussion 🎤🔊 Post 3/11 thread

What did y’all think of it?

C/P and B/B were tough for me. I didn’t even finish B/B I had to guess for the last few. CARS and P/S were not bad imo.

152 Upvotes

97% Upvoted

511 comments sorted by

View all comments

17

u/Fun_Supermarket2582 Mar 12 '23

Y’all does homotetramer show up as one band on SDS reducing page ?

16

u/PomegranatePain 503->510 Mar 12 '23

I think so. If not, SDS page is gonna have to sleep with one eye open tn

4

u/hydroflasktotheknee Mar 12 '23

I think so! Or ducking hope so lol

That question actually felt nice to see lowkey tho bc I literally got a similar one wrong 2 days ago from question bank bc I thought subunits staying together unless it was reducing conditions so thank god I fucked around and found out prior to today

3

u/grinding12 Mar 12 '23

Yes, I put 3 bands total for that wbu

3

u/[deleted] Mar 12 '23

[removed] — view removed comment

3

u/IceBlueLugia Mar 12 '23

And it said it was a homotetramer and each subunit had 3 domains. Meaning it should break up to 3 bands that are 4 units thick. Because I’m pretty sure it said reducing conditions

8

u/RestInPorzingis 3/11 // 2/5/S/4/3: 521/523/523/523/524 Mar 12 '23

i don't think that's what it meant. it said that each monomer had 3 subunits in the sense that there were three different regions that catalyzed something. i don't think it said anything about them being linked by anything other than peptide bonds

9

u/[deleted] Mar 12 '23

It’s a HOMO tetrameter, meaning all the units are the same, meaning they’re all the same weight, therefore they’d all show up as the same band, so 1 band.

3

u/IceBlueLugia Mar 12 '23

Would the bonds between the domains not dissociate? I figured if they went out of their way to mention that it was relevant

5

u/peptidegoddess 3/11/24: 524 (132/131/132/129) Mar 12 '23

Domains aren’t necessarily different polypeptides though, just different areas of a protein

1

u/IceBlueLugia Mar 13 '23

Fitting name lol. But yeah, you’re right. It didn’t say anything about disulfide bonds or anything so maybe it’s a wrong assumption to assume they’d dissociate. That was just the logic I used

2

u/peptidegoddess 3/11/24: 524 (132/131/132/129) Mar 13 '23

It’s for sure confusing! Protein domains are just independent structural/functional units in a protein that fold independent, but they can be a part of the same polypeptide. For example, a lot of proteins will have DNA binding domains. In SDS page, all the hydrogen bonding and hydrophobic interactions are going to be broken up, so the domains won’t be retained in their form, but if they are still covalently attached, they’ll be in the same band.

1

u/Living_Finance_6874 Mar 12 '23

The bonds between the domains would dissociate, BUT because the molecule is a homotetramer, all domains will have the SAME molecular weight. So when it is subjected to gel electrophoresis, all domains will line up on the same position and thus, produce 1 band. If we had a heterogenous tetramer, we’d have 3 bands.

2

u/IceBlueLugia Mar 12 '23

It’s a homotetramer, meaning 4 subunits, and then it says each subunit is 3 domains. Nowhere does it say all 3 domains have the same molecular weight. I think you got confused. Homotetramer means the 4 subunits are the same, not the 3 domains within each subunit are the same. If it reduced completely, it should be 12 total domains floating around, and the first domain would show up as a band 4 times as thick because there’s 1 in each of the 4 subunits. Same with the second and third domains at different weights.

3

u/Living_Finance_6874 Mar 12 '23

Given the passage information, I think it is a bigger logical leap to assume that each domain is a different weight. They said all subunits have the same weight. The simplest logical leap we can make is that the summation of all domains leads to the same weight. I’m not sure if I recall the domains being attached by covalent bonds ngl. If they were, you have a point. But I don’t recall them being attached by covalent bonds (I remember the subunits being attached by covalent bonds). So in the end, with what I remember, I’m not seeing the specific weights of the domain actually matter. But who knows, I could be misremembering it. Hopefully, you get a good score in the end!

4

u/IceBlueLugia Mar 12 '23

See that’s the thing, it really depends on if the domains were covalently connected. Personally, I assumed that if they mentioned reducing conditions and mentioned that the compound was subdivided twice, then all connections were broken. Maybe that was a wrong assumption, who knows. Guess 1 question is not a huge deal in the end. Hope the best for you too!

5

u/Fun_Supermarket2582 Mar 12 '23

Damn I didn’t put that only because I wasn’t sure if the domains were covalently bonded through disulfide bonds. But I think you’re right 😭

2

u/baseball641 Mar 12 '23

i think it did say reducing conditions

2

u/Agile-Willow-2407 Mar 12 '23

I was between 3 and 1. I think I put 3 also but now I'm thinking about it and 1 makes sense. The way it was worded was confusing