Question

So i'm having some trouble, i'm supposed to figure out the temperature at which a protein denatures:

\(protein_{native} \rightleftharpoons protein_{denatured}\)

i have: \(\Delta G^o=-RTln(K_{eq*folding}\)

\(\-321.2 J/mol=-(8.314 J/mol)(T)ln(K_{eq*folding}\)

i know the protein will denature when \(K_{eq*folding\)<1

but i can't set it to 1, because ln(1)=0, if use ln(0.99) i get like 3800 K, which is nonsense.

I tried taking the limit as \(K_{eq*folding\rightarrow 1-}\) but i get infinity. What do?

Answer 1

Hmm... is it when K\(_{eq}\) < 1 or <0?

Answer 2

\(K_{eq}<1\), because it's the reverse process

Answer 3

I feel like I should know this, my last class senior year was a protein biochemistry lab.
If i remember: \(\sf \color{red}{ [D_{eq}] + [N_{eq}]=1}\)

Answer 4

hmm, that makes sense. but i don't know how i can use that

Answer 5

i'm gonna graph it on excel and see what happens

Answer 6

Yeah, show me the graph.

Answer 7

okay i'll post it, give me 2 mins

Answer 8

You can mayb see the point of fractional denaturation.

Answer 9

\(\Delta\)G\(_o\) = -RT + ln\(\sf \color{purple}{\frac[D_{eq}}{1-[D]}\)

Answer 10

ugh. stupid LaTex, Im trying to type it out beautifully. Lol

Answer 11

haha i know it screws up on me too sometimes. So i just put all the constants together, and typed into wolfram because it's easier. http://www.wolframalpha.com/input/?i=T%3D38.63%2Fln%28K%29

Answer 12

theres an asymptote at K=1

Answer 13

Did you just use temp to denature?

Answer 14

we'll i'm trying to find the temp at which it denatures. The initially gave me some data, and i found the thermodynamic parameters H, S, G for the folding process. And now, it's asking me to find the temp at which the protein denatures.

Answer 15

so i figured that implies that Keq<1

Answer 16

I would use \(\Delta\)G = \(\Delta\)H-T\(\Delta\)S in that case.

Answer 17

so should use that and set \(\Delta G\)>0, for the folding reaction. Sorry, i'm tired lol

Answer 18

It's ok. I should be studying right now for my microbiology exam tmrw morning but I'm on here \(\sf \color{pink}{:P}\) cuz now its bothering me that I don't rmr :/

Answer 19

And yeah. Are you familiar with the van't hoff equation? I think this is similar.

Answer 20

yeah, i was thnking about that, but, again, I'm not sure what i would set the ratio of the equilibrium constants to. Dude, i appreciate your help, but you should go study if you have an exam! lol i'll definitely msg you the answer (i'll ask my prof tmrw) if you're interested.

Answer 21

haha i know! it gets pretty addictive. Nah man, you're a smart mofo, sometimes getting the answer is just not possible because there's not enough info n $h!t. But yeah, i'll let you know, peace !

Answer 22

So, to find the denaturation temp, i had to use \(\Delta G=\Delta H-T\Delta S\)

and at equilibrium \(\Delta G=0 \)

and thats it lol

Answer 23

@abb0t

Answer 24

OMG, I was right. HAHA

Answer 25

I think you could of used the slope also, which is something like \(\frac{\Delta S}{\Delta H}\) i think?