Kt vs. Km? AAMC sample test bio passage #5

[lostnconfused]

Can somebody please explain the relationship between Kt and Km to me? Neither variables are actually mentioned in the passage. Are we just suppose to assume Kt is equal to Km or is there an actual relationship between Kt & Km that I am missing?

Thank you!

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[theonlytycrane]

Kt is like Km in the michaelis-menten model, except "t" standing for transport. IMO, it's a bit silly when they do this but just apply prior knowledge of content to equate Kt = Km and Jmax = vmax.

 

[salemstein]

I've also seen Kd and Kc being used before. Also treat them as another version of "Km" ?

 

[theonlytycrane]

@salemstein Kc is for equilibrium so we would expect to see this in the content of an equilibrium concentration. Kd (d for dissociation) is like Km in the michaelis-menten model, but may also be used in other contexts.

 

[cwillman044]

I've also seen Kd and Kc being used before. Also treat them as another version of "Km" ?

Kd is different from Km. Kd is the dissociation constant, something with a high Kd is going to want to dissociate more so it will have a weaker binding affinity.

 

[theonlytycrane]

Kd is different from Km. Kd is the dissociation constant, something with a high Kd is going to want to dissociate more so it will have a weaker binding affinity.

In the michaelis-menten model Km is the Kd for the ES complex, which is inversely proportional to the enzyme-substrate binding affinity.

 

[aldol16]

Can somebody please explain the relationship between Kt and Km to me? Neither variables are actually mentioned in the passage. Are we just suppose to assume Kt is equal to Km or is there an actual relationship between Kt & Km that I am missing?

You're overthinking it. The question is asking you to draw a simple analogy between a part of a system that you know and a part of a new system that's presented to you. It's the equivalent of saying "Here's a car you've never seen before. What's the piece of glass between the front end of the car and the driver if it's called the same thing as the corresponding part is in your car?" So you would have to know that in your car, that's the windshield and if the same terminology is used in the new car, it should also be called the windshield and its function must also be to prevent particles from flying into the passenger compartment.

 

[lostnconfused]

In the michaelis-menten model Km is the Kd for the ES complex, which is inversely proportional to the enzyme-substrate binding affinity.

!! I did not make this connection. Thank you!

And yeah, I have seen Kd used in terms of "A binds to B with a Kd of #," which seems contradictory at first since Kd normally stands for dissociation.

It's so confusing with all the K's. I assumed Kt was being used in the same context as Km but it just made me really uncomfortable. But then again that seems to be AAMC's goal.

Thank you everyone for your help!