question 568, Nextstep MCAT Science Qbook, Biochemistry section, page 93
They have given a lineweaver Burk plot and asked to find the Km value. They haven't given the coordinate points for Xaxis so I don't get it how did they got 3/2 or slope. Can you please explain me the math here please and how id they got the Km value of 1/2?
QBook biochem query
QBook biochem query
Kind Regards,
Arushana Ali.
Arushana Ali.

 Posts: 192
 Joined: Fri May 25, 2018 9:15 am
Re: QBook biochem query
Thanks for your question!
On a LineweaverBurk plot, we can always find Km or Vmax from the slope, provided we have one of them. Remember, the reciprocal of the yintercept will give us Vmax and the negative reciprocal of the xintercept will give us Km. The equation we can use is:
slope = Km / Vmax
In this case, we can solve for slope using the points and coordinates we were given. I learned slope as rise over run... in this case we have a rise (y) of 3 and a run (x) of 2. So, our slope is 3/2 or 1.5. We also know our Vmax, since it is the reciprocal of the yintercept: 1/3.
So:
slope = Km / Vmax
(3/2) = Km / (1/3)
(3/2)(1/3) = Km = 1/2
I hope this helps!
On a LineweaverBurk plot, we can always find Km or Vmax from the slope, provided we have one of them. Remember, the reciprocal of the yintercept will give us Vmax and the negative reciprocal of the xintercept will give us Km. The equation we can use is:
slope = Km / Vmax
In this case, we can solve for slope using the points and coordinates we were given. I learned slope as rise over run... in this case we have a rise (y) of 3 and a run (x) of 2. So, our slope is 3/2 or 1.5. We also know our Vmax, since it is the reciprocal of the yintercept: 1/3.
So:
slope = Km / Vmax
(3/2) = Km / (1/3)
(3/2)(1/3) = Km = 1/2
I hope this helps!
Re: QBook biochem query
Thank you that makes sense. In the book the picture there was no labelling on Xcoordinates given so the coordinates for X are 2,0 right? I have another question this is from Biochem page 115, question 700. What does steric probability means? It says cells can utilize cell uses enzymes to increase steric probability to drive nonspontaneous reaction what does it mean?
Kind Regards,
Arushana Ali.
Arushana Ali.

 Posts: 192
 Joined: Fri May 25, 2018 9:15 am
Re: QBook biochem query
Steric probability is essentially referring to an enzyme's ability to orient molecules correctly so that a specific, catalyzed reaction can occur. Enzymes can contort, or bend, or orient substrates so that the activation energy is lower. I'm sure you're familiar with the concept, it's just a new vocab term to refer to it!
Re: QBook biochem query
Question 843, page 138, biohem question. I am not sure if I understood the question. Can you explain me how to approach this? I particularly did not understand the shifts of loop in response to depolarization. Your explanation will make much more sense.
Additionally, question 775, page 125 it says three phases of pentose phosphate pathway? Is it referring to the oxidative and non oxidative phase? If so what is the third phase then?
Also page 113, question 686 biochem the answer is Pka2 and explanation says side chain carboxylic acid is represented by Pka2. I thought Pka3 is the side chain Pka. Can you explain me this?
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Additionally, question 775, page 125 it says three phases of pentose phosphate pathway? Is it referring to the oxidative and non oxidative phase? If so what is the third phase then?
Also page 113, question 686 biochem the answer is Pka2 and explanation says side chain carboxylic acid is represented by Pka2. I thought Pka3 is the side chain Pka. Can you explain me this?
Question 835, page 135, the answer to this question is that the student is correct. In question the triphosphate is attached to 2 carbon as opposed to 5 carbon. I was comparing the structure so saw carbon 1 has base, 2 has just hydrogen, 3 has OH, 4th carbon is attached to 5th carbon which is then attach to phosphate. Can you explain this difference?
Kind Regards,
Arushana Ali.
Arushana Ali.