Hi,
I was hoping someone could explain the difference between or somet tips to recognize when a question is talking about the Km or Kd of an enzyme versus Ka or Ksp. Usually they are very distinct and I am able to tell the two apart but I was doing some deliberate practice in the chemistry section and I was really confused.
For q52, chem section of the altius 8 FLE the question relates to stability constant and they were asking what formula would be used to calculate the stability constant (Ks) of the most stable interaction. I got confused because I wasn't sure if I should choose the one with the highest Ks listed in the table or the one with the lowest.
The reason I was drawn to the lowest one was because I related it to Km of an enzyme where a low Km means a high affinity. However it ended up asking for something more similar to equilibirum constants (Ka, Ksp, etc)
Yeah, I don't love this question because it is a bit vague of what direction the Ks is defined as. However, usually when I don't get much information and I see a K for it that is not Ka or Km, I assume that the forward reaction is from left to right (which I think is the key to this question).
I have noticed that Kd also has a similar concept as Km (AAMC BIO Section Bank q47). Is this the only one thats similar to Km?
Overall I was wondeirng if there are certain letters that mean its more similar to Km (in that a low value = more stable more affinity) and certain letters mean its more similar to equilibrium constants like Ka or Ksp etc.
Yeah, Km and Ka are similar, but be a little careful in grouping them too close - Ka and Kd are Keqs representing distributions of products and reactions as according to thermodynamic equilibrium.
Because Ka is the inverse of Kd.
In contrast, Km is derived from rates of enzyme catalysis and is similar to Kd in that the lower that it is, generally more binding is happening. However, they are not exactly the same as Km is defined as the concentration of substrate where you have a rate of 1/2Vmax (which is a kinetic argument).
In short, assume that your forward reaction is from left to right except when explicitly asked to view things from a Kd or Km perspective.
I hope this helps, please let me know if this is unclear.
Katt