EK 1001 Biology question

[ACSheldor]

I'm not sure if I'm completely insane or if there is some kind of mistake somewhere.
Anyway, in EK 1001 Biology book, in chapter 5 question 541, answers B and D both look correct to me.
Let me give you the information in case you don't have the book:

The passage gives 4 equations which are:

- Metabolic Clearance Rate (MCR) = rate of hormone elimination / plasma hormone concentration

-Volume of distribution (VD) = is the total amount of hormone in the body

Fractional turnover rate = MCR/VD

-Half life = 0.7* VD/MCR

So the questions asks: all of the following will decrease the expected hormone half-life except:

A. a decrease in the total hormone in the body

B. a decrease in the fractional turnover rate

C. an increase in the metabolic clearance

D. an increase in the plasma hormone concentration

So as I was doing the question I eliminated A and C right off because those were obvious. I ended up putting D and got it wrong and the explanation said that increasing plasma hormone will increase MCR.

My question is: How and in what universe?

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[RogueUnicorn]

my guess without the rest of the passage is that it's not MCR that's constant, but rate of elimination. thus, if you increase concentration, to maintain the rate of eliminiation you must elevate MCR. just a guess, hard to know without the full passage.

 

[ACSheldor]

my guess without the rest of the passage is that it's not MCR that's constant, but rate of elimination. thus, if you increase concentration, to maintain the rate of eliminiation you must elevate MCR. just a guess, hard to know without the full passage.

Hmmm, very interesting. I think you might be right. Of course the passage nor the explanation say anything about this, but that would at least make sense.

Thank you so much for you help bleargh.

The passage really doesn't mention the elimination rate at all nor the MCR being variable or constant but then again this is EK and it isn't the first time I've seen a shaky question. I hope the MCAT doesn't have questions that are as unsupported as some of the EK questions. I hear they are a bit more straight forward so here's to hoping for that.

 

[RogueUnicorn]

MCAT questions are VERY fair, rest assured.

 

[ACSheldor]

I hope you're not being sarcastic but Thanks, it really helps knowing that.

 

[RogueUnicorn]

i am not. you'll see when you take the FL aamc tests

 

[dudechiefboss]

^yeah, I thought D was also right!?

 

[ACSheldor]

Okay, I'll choose to believe you. Thanks for your help.

 

[Vanguard23]

Here's another from EK 1001. Question 373:
Uncouplers specifically increase proton permeability. According to the passage, uncouplers can be grouped into the same category as which of the following:
A. ATP Synthase inhibitors (the one I chose).
B.Electron transport chain blockers
C. Proton transport inhibitors
D. Hydrophobic Carrier molecules (the correct choice).

Ok, here's my problem. From the passage:

"Amphipathic weak acids are uncoupling agents that transport protons across the inner mitochondrial membrane, dissipating the energy of the transmembrane proton gradient and preventing the production of ATP. While maximum rates of electron transfer are reached, because the translocated protons do not cycle through the ATP-synthase, no ATP is produced."

Choice D is explained, but it is not explicitly stated in the passage, as choice A pretty much is. Choice A appears to be the more obvious correct answer.
In fact, the answer gives more information than the passage provides about them being hydrophobic.

Ridiculous.

 

[RogueUnicorn]

Choice A is wrong simply because an enzyme inhibitor has nothing to do with shuttling protons across a membrane.

 

[ACSheldor]

Choice A is wrong simply because an enzyme inhibitor has nothing to do with shuttling protons across a membrane.

I have to agree with bleargh. How I saw that question was: if electrons were to flow down the gradient then would the atp synthase work? Of course it would, so why isn't it working now with the uncoupler? Because it's energy supply has been taken away (proton gradient). If you created a proton gradient it would still work so it isn't in itself inhibited. The passage says nothings been blocked so it's not B or C because the protons flow fine. The thing is that channels have been added that allow protons to go down the gradient so it has to be D. This is a question that is more answered by process of elimination rather than trying to find one correct answer.

Don't worry about it though, just working on bending your mind to fit the logic until it makes sense to you. You learn really quick what they're looking for and that a lot of times the answer is found by eliminating answers rather than picking one out. So instead of finding the best answer it might be more help to find the least wrong answer.

 

[Vanguard23]

Choice A is wrong simply because an enzyme inhibitor has nothing to do with shuttling protons across a membrane.

it says nothing about being an enzyme inhibitor. Just an inhibitor of ATP-synthase and then goes on to contradict itself.

 

[RogueUnicorn]

it says nothing about being an enzyme inhibitor. Just an inhibitor of ATP-synthase and then goes on to contradict itself.

uncouplers do nothing to ATP-synthase. ATP synthesis can still occur technically, though at a much reduced rate due to decreased proton motive force. just tryin to help you understand, i have no idea what the passage says

 

[Vanguard23]

uncouplers do nothing to ATP-synthase. ATP synthesis can still occur technically, though at a much reduced rate due to decreased proton motive force. just tryin to help you understand, i have no idea what the passage says

I quoted the passage.
"because the translocated protons do not cycle through the ATP-synthase, no ATP is produced.""
Would that inhibit the actions of ATP-Synthase? Yes. What's the noun for something that inhibits the actions of something? An inhibitor.
My point against the shuttle is that it doesn't say anywhere what it's nature is. A carrier molecule could have been a protein, a vacuole or a number of things that don't necessitate being hydrophobic.

 

[RogueUnicorn]

I quoted the passage.
"because the translocated protons do not cycle through the ATP-synthase, no ATP is produced.""
Would that inhibit the actions of ATP-Synthase? Yes. What's the noun for something that inhibits the actions of something? An inhibitor.
My point against the shuttle is that it doesn't say anywhere what it's nature is. A carrier molecule could have been a protein, a vacuole or a number of things that don't necessitate being hydrophobic.

no. it doesn't inhibit ATP synthase. you are using the word colloquially, not scientifically. the protons do not cycle through the ATP synthase, but it doesn't mean they couldn't. nowhere in that sentence is the implication that ATP synthase is inactivated (noncompetitive inhibitor) nor any implication something is outcompeting protons (competitive inhibitor)

edit: to try to illustrate in a different way, if i sucked out all the protons from the intermembrane space, would there be ATP synthesis? no. did that do anything to the enzyme? again, no.

 

[ACSheldor]

I quoted the passage.
"because the translocated protons do not cycle through the ATP-synthase, no ATP is produced.""
Would that inhibit the actions of ATP-Synthase? Yes.

No, this is where you went wrong. You need to ask yourself why they aren't cycling. Or more importantly, why are they cycling to begin with? The protons cycle because they go from a point of higher concentration to a point of lower concentration when they move through the synthase. Since protons can't move through a lipid bilayer, the synthase is the ONLY place they can cross over from a high concentration side to a low concentration side. Now if you added uncouplers then the protons don't have to move through the synthase anymore, they can just go down the uncouplers and be on the other side. Does that mean that the synthase doesn't work? No, the synthase works it just doesn't have protons running through it because the protons are getting into the cell from other routes.

What's the noun for something that inhibits the actions of something? An inhibitor.

An inhibitor is something that doesn't allow another thing to perform its proper function. So, if you were a proton could you still move through the synthase? Yes you could, so the synthase is not being inhibited.

My point against the shuttle is that it doesn't say anywhere what it's nature is. A carrier molecule could have been a protein, a vacuole or a number of things that don't necessitate being hydrophobic.

To add to what blergh said, think of it like this:

The reason there is no ATP is because there is virtually no flow of protons. If you took that pump and put it in another cell the it would produce ATP because that cell would have a proton gradient.

If the synthase had been inhibited by a toxin or chemical then even when you took it out and moved it to another cell it wouldn't work because the binding site or shape of the actual synthase is messed up.


So let me give you a visual example: - is the membrane, S in the ATP synthase, U is the uncoupler, and + are protons

-------------------------------------------------------------------------------------
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
----------------------------------S-------------------------------------------------
--------------------------------+
So in the picture above, all of the protons have to go through the synthase to get to the other side. When the protons go through the synthase ATP is produced.

Now if you added uncouplers:

-----------------------------------------------------------------------------
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
U---U---U---U---U---U---U---U-S-U---U---U---U---U---U---U---U---U--
+---+---+---+---+---+---+---+-+-+---+---+---+---+---+---+---+---+

Now in this picture, the protons can go through the synthase as before OR they can go through the uncoupler to get to the other side. So protons are still going through the synthase, just not as much anymore because now they can go through the uncouplers. The synthase still produces ATP but at a much much reduced rate because the protons can go through 17 other uncouplers instead of the synthase.

If this doesn't make sense then I'm not sure how else to explain it.

 

[Charles_Carmichael]

I quoted the passage.
"because the translocated protons do not cycle through the ATP-synthase, no ATP is produced.""
Would that inhibit the actions of ATP-Synthase? Yes. What's the noun for something that inhibits the actions of something? An inhibitor.
My point against the shuttle is that it doesn't say anywhere what it's nature is. A carrier molecule could have been a protein, a vacuole or a number of things that don't necessitate being hydrophobic.

I'm confused by your statement here. You know the membrane is made of lipids. So you know that the carrier molecule has to be hydrophobic in order to traverse the membrane. There was no need for the passage to explicitly tell you that the carrier is hydrophobic since you should have this knowledge (regarding the membrane) already. You should've used this prior knowledge to answer the question.

Also, the uncoupler is not inhibiting ATP synthase; it's not an inhibitor. The uncoupler, as bleargh mentioned, is screwing with the proton motive force by carrying protons across the membrane without letting them pass through ATP synthase. It has nothing to do with inhibiting the actions of ATP synthase at all. ATP synthase will continue to function as it normally would...taking away some substrate (ie. protons) doesn't mean you're inhibiting the enzyme.