QBook biochem query

aru
Posts: 15
Joined: Thu Jul 05, 2018 12:41 pm

QBook biochem query

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 X-axis 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?
Kind Regards,
Arushana Ali.
NS_Tutor_Will
Posts: 395
Joined: Fri May 25, 2018 9:15 am

Re: QBook biochem query

On a Lineweaver-Burk plot, we can always find Km or Vmax from the slope, provided we have one of them. Remember, the reciprocal of the y-intercept will give us Vmax and the negative reciprocal of the x-intercept 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 y-intercept: 1/3.

So:

slope = Km / Vmax

(3/2) = Km / (1/3)

(3/2)(1/3) = Km = 1/2

I hope this helps!
aru
Posts: 15
Joined: Thu Jul 05, 2018 12:41 pm

Re: QBook biochem query

Thank you that makes sense. In the book the picture there was no labelling on X-coordinates 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.
NS_Tutor_Will
Posts: 395
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!
aru
Posts: 15
Joined: Thu Jul 05, 2018 12:41 pm

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?
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.
NS_Tutor_Will
Posts: 395
Joined: Fri May 25, 2018 9:15 am

Re: QBook biochem query

Q843: The basic idea here is that the s-loops allow the protein to change its conformation—or, in this case, you could think of it as its relative position in the membrane. In order to not be blocking the pore (through which ions can be transported), the s-loop needs to be moved away from the membrane. We also know that when cut out completely, ions move freely, implying that the s-loop blocks the pore. Further, when replaced with alanine, we don't see the same activity that we see with whatever residues the s-loop actually has. Since depolarization leads to the pore opening and depolarization is moving in the positive direction, we can conclude that the s-loop should be made of positive residues because the depolarization process would repel that region.

Q775: I usually think of the PPP as having the two phases you mentioned. It looks like this question refers to the isomerization phase as a distinct phase. It's trivial, though -- don't worry about it!

Q686: Typically, you'll think of pKa order as going from lowest to highest. So, c-terminus is pKa1, sidechain for acidic (and basic) amino acids is pKa2, and n-terminus is pKa3. For non-acidic, non-basic amino acids, the c-terminus is pKa1 and the n-terminus is pKa2.

Q835: I'm not sure I fully understand your question. Nucleotides have a nitrogenous base, a five-carbon sugar, and 1+ phosphate group(s). The phosphates don't have to be attached at the 5-c position, they just happen to be with ATP so we're used to seeing them that way.

Hope these help!
aru
Posts: 15
Joined: Thu Jul 05, 2018 12:41 pm

Psychology + Biochem

I came accross to these two new terms Can you explain me this ? Rosy retrospection, Defensive attribution Hypothesis, Zeigarnik effect and Karen Horney basic anxiety hypothesis. If you can provide example or situations in which they are applied it would be great as I feel that it really helps to memorize if the concept is paired up with specific examples.
"The process occurring here is sensitization, or an increase in response after repeated exposures to the same stimulus" Q29, Psychology online QBank 3. Can you explain me acc. to the explanation provided for this question how is sensitization increasing the response. I thought after repeated exposure to stimulus, receptor reduces their sensitivity and so does our response decreases. Can you explain me where I am approaching this incorrectly?
"A teenager flips a coin ten times and gets heads eight times; he concludes that the next flip will probably be tails." Question 20, Psychology QBank 4, I don't understand how is this an example of representative heuristic. Also I can't seem to grasp the relation between gambler's fallacy and representative heuristic. I feel like both of their explanations has nothing to do with each other but the way explanation elaborates this, I can't seem to grasp the concept. I will appreciate your explanation.
Kind Regards,
Arushana Ali.
NS_Tutor_Will
Posts: 395
Joined: Fri May 25, 2018 9:15 am

Re: QBook biochem query

Hi Aru,

Rosy retrospection: looking back at the past in a more positive way as compared to how you'd look at the present. An example could be looking back on high school as a particularly great time when it may not have been that great in reality.

Defensive attribution: basically the idea that you will dismiss the likelihood of something bad happening to you when you hear about it happening to other people. If the person is similar to you, you would assign responsibility to them. For example, if you heard about someone like you being injured in a car crash, you might say "they must have been texting" or "they must have been a bad driver."

Zeigarnik effect: the idea that people remember unfinished tasks better than they remember finished tasks. The classic example is a server remembering who ordered what at a restaurant table before the bill is paid, but then forgetting them all once the bill is paid.

Basic anxiety hypothesis: the idea that neuroses arise from anxiety about interpersonal relationships. The strategies that we use to respond to that anxiety can cause "needs" to crop up (i.e. need for affection or need for prestige). It's not something that I think is likely to come up on the MCAT, but think of it as interpersonal anxiety leading to neurosis and particular needs.

Q29 from Psych QBank 3: The phenomenon that you are describing is habituation. Since we are told that the person has a stronger reaction to the same stimulus, we must choose sensitization because that fits the described pattern. You might expect habituation to occur, and it certainly could, but in this example, only sensitization fits (because the person grew more sensitive to the stimulus).

Q20 from Psych QBank 4: The coin flipping is an example of the representative heuristic because the teenager is using the events that have occurred in the past to inform their expectation of the next event. Because the events are entirely independent, this is a fallacy. This is the same thing as the gambler's fallacy, because you're assuming past events can be used to interpret current or future events, but, in the case of independent events (like cards, or other gambling games) this is not the case. The outcome of a particular event does not depend on the outcome of earlier events.

I hope this helps!
aru
Posts: 15
Joined: Thu Jul 05, 2018 12:41 pm

Re: QBook biochem query

According to biological game theory, which strategy will ultimately prevail in a species of coyotes: a fighter strategy or an avoider strategy? Q 49, Psychology QBank 4.
Can you briefly explain me this biological game theory? Is it referring to the same concept as evolutionary theory? There is a hawk-dove example given in explanation which I am not sure if I understood this while reading online since it is very new concept to me. Never learned it in pysch class. If you can explain it in your words or provide a link where it is presented in easy wordings that will be awesome.