qd 2118 UW on Gibbs free energy? plz help

[sadaca]

hey guys, Does anyone know how to do these in a simple manner? I have gotten 2 qs from UWORLD and both I don't even understand the explanation. If you know how to approach this plz share . Its QD 2118 and 2119 on GIBBS FREE ENERGY

Appreciate it,

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[Nephronlearner]

hey guys, Does anyone know how to do these in a simple manner? I have gotten 2 qs from UWORLD and both I don't even understand the explanation. If you know how to approach this plz share . Its QD 2118 and 2119 on GIBBS FREE ENERGY

Appreciate it,

I haven't done the UWORLD Qbank but Gibbs free energy tells you whether the reaction (probably the pathway) happens spontaneously or not. Negative free energy (related to positive universe entropy) means the process is spontaneous. By subtracting the energy of production of reactants from the energy of production of products you get the free energy change for that particular reaction.
For instance, I believe hydrolysis of ATP: ATP ----> ADP + Pi has dG ~ -30 kJ/mol
Reaction happening in reverse would have the opposite sign ( +30 kJ/mol)
Perhaps they wanted you to use it to add a spontaneous and non-spontaneous reaction?

Hope it helps!

 

[sadaca]

hey buddy thanks alot for your help. I am still lost but thats okay! Maybe if u accross the uworld qs you can msg me then , if its the same approach?
Thank you =)

 

[Nephronlearner]

hey buddy thanks alot for your help. I am still lost but thats okay! Maybe if u accross the uworld qs you can msg me then , if its the same approach?
Thank you =)

What do you need to calculate? If you need the change in Gibbs free energy then just do the products - reactants calculation.

Also there is another equation you may find useful: dG = -RT ln K (and K is constant, aka product/reactant)

 

[notbobtrustme]

you don't need to calculate anything, it's simply an equilibrium question.

The question asks which substrate will dominate. I believe it was G6P -> F6P, dG = +30kJ. At that point, you know that G6P will dominate because the delta-G is positive and thus favors the left (whoops, had right at first, sorry about that) hand side of the equation. The question then asks what the equilibrium constant will be, but you don't have to do any calculations. Remember that equilibrium is equal to products/reactants. The answer choices, IIRC, were 0, 0.5, 1 and 1.5. 0 is a junk answer, no Keq is 0. 1 is perfect equilibrium (eg dG = 0), and 1.5 favors the right. The only answer choice is 0.5, which means that the left side is favored.

F6P/G6P = Keq, G6P > F6P at equilibrium, thus, the answer has to be less than 1.

 

[sadaca]

hey! okay I get it now!! So if its G is positive, then it has to be less than 1, its favoring the SUBSTRATES(what you start with) and if G is neg, then reaction is favoring the products(What you get), and it is greater than 1.

Thanks alot buddy!

 

[sadaca]

Can I ask you another q from uworld, not related to this plz? Its qd 0109 on CANDIDA. In this question,what is candida causing?
I know it uworld says it can any go to any organ but who do we know this is candida infecting this guy? The pic looks like crytococcus to me. I really appreciate your help and time.

 

[Nephronlearner]

you don't need to calculate anything, it's simply an equilibrium question.

The question asks which substrate will dominate. I believe it was G6P -> F6P, dG = +30kJ. At that point, you know that G6P will dominate because the delta-G is positive and thus favors the right hand side of the equation. The question then asks what the equilibrium constant will be, but you don't have to do any calculations. Remember that equilibrium is equal to products/reactants. The answer choices, IIRC, were 0, 0.5, 1 and 1.5. 0 is a junk answer, no Keq is 0. 1 is perfect equilibrium (eg dG = 0), and 1.5 favors the right. The only answer choice is 0.5, which means that the left side is favored.

F6P/G6P = Keq, G6P > F6P at equilibrium, thus, the answer has to be less than 1.

notbobtrustme is right! I haven't seen the question (as I haven't done UWorld) so I couldn't know what was asked.
G6P -> F6P is indeed a very simple equilibrium question.
Anyway, sadaca, general concept (as I told you in the 1st message) behind Gibbs energy is whether the reaction is spontaneous, aka in which direction it spontaneously goes. If it is negative, it favours products formation. If it is positive, products aren't spontaneously made, thereby you have more reactants (in this case G6P).

Keq=products/reactants
So if there is equal number of products and reactants then Keq = 1
More products: Keq>1 (higher/lower number)
More reactants: Keq<1 (lower/higher number)
In order for Keq to be 0 there would need to be no products at all, which isn't a realistic scenario.

The same can be calculated but with the answer choices you were given it isn't necessary as 0.5 is the only one lower than 1.

 

[notbobtrustme]

Can I ask you another q from uworld, not related to this plz? Its qd 0109 on CANDIDA. In this question,what is candida causing?
I know it uworld says it can any go to any organ but who do we know this is candida infecting this guy? The pic looks like crytococcus to me. I really appreciate your help and time.

sure, this question is basically two parts. 1 -> he's immune compromised and probably neutropenic because of chemotherapy and 2-> the picture shows yeast + germ tubes, which is diagnostic for Candida.

neutropenia + fungicemia = candidasis 99% of the time.

 

[sadaca]

Hey thanks @Nephronlearner , I def. get it now. Its not bad at all! =)

@notbobtrustme - Thank you again, so for this q, it is just causing canademia, just genearl non specific symptoms? And you knew it was Candida b/c of the picture mainly?? B/c the other options are also opportunistic seen in Neutropenic patients and can be cultured at 97% (mold)

ThankS!

 

[notbobtrustme]

Hey thanks @Nephronlearner , I def. get it now. Its not bad at all! =)

@notbobtrustme - Thank you again, so for this q, it is just causing canademia, just genearl non specific symptoms? And you knew it was Candida b/c of the picture mainly?? B/c the other options are also opportunistic seen in Neutropenic patients and can be cultured at 97% (mold)

ThankS!

yea, the clinical picture can suggest a bunch of other things, but the most common fungicemic organism is Candida. The picture clinches it because it shows yeast + germ tubes at 37C, of which only Candida can produce such a picture.

 

[sadaca]

Great, I understand now. Thank you buddy