biology mcat questions...

[mj6969]

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Which of the following statements is true of the outer and inner mitochondrial membranes?

A The outer membrane is mostly lipid and the inner membrane is mostly protein.
B The inner membrane is mostly lipid and the outer membrane is mostly protein.
C The inner and outer membranes are very similar with regard to amount of protein and amount of lipid.
D None of the above.


The ATPase in the inner mitochondrial membrane makes ATP using energy derived directly from

A A high energy phosphorylated metabolic intermediate
B An electron gradient across the inner mitochondrial membrane.
C A proton gradient across the inner mitochondrial membrane
D Glycolysis

 

[bigman225]

taking a stab
1. A
I believe that ETC protein complexes make the inner mitochondrial membrane an outlier in terms of protein/lipid composition: it contains a much higher % protein.

2. C
basic ox-phos knowledge, protons movement creates rotation of proteolipid ring, etc etc

 

[bodonid]

taking a stab
1. A
I believe that ETC protein complexes make the inner mitochondrial membrane an outlier in terms of protein/lipid composition: it contains a much higher % protein.

Good logic. I agree there is a higher % protein in inner than in the outer, but no matter how many metabolic proteins there are, I don't think they would outnumber the number of lipid molecules. I say D. Any more takers?

Update: (just to confuse you)
By concentration
Outer mitochondrial membrane 50:1 lipid/protein
Inner mitochindrial membrane 15:1 lipid/protein
By mass
Outer mitochondrial membrane 1:1 lipid/protein
Inner membrane 1:3 lipid/protein
So, which did they mean? Anyone? Either way, I still don't know the answer.

 

[Vihsadas]

Wow. I can't believe how fast I'm forgetting this stuff! Let me take a stab:

Endosymbiont hypothesis: Outer membrane will be similar in structure to a normal eukaryote membrane => mostly lipid.

The prokaryote membrane (inner mito membrane) is a little different in composition to the outer Mem (prok vs euk) and in addition, because of the ETC complexes the protein content will be higher. Now, I think that depending on whether you are considering via total mass or concentration you're going to get two different answers (because the membrane proteins are very different in size when compared to lipids).

I'm thinking that by concentration You'll have something like IMM is 10 to 1 in favor of lipid, and by mass you'll have something like 1 to 1 or 2 to 1 in favor of protein.
mmmm...

Given that, its either A or D depending on how your measuring total protein content. The MCAT will most likely test total Mass so I would pick 'A' if confronted with this on a real MCAT. That being said, I think the question si flawed. 😛

Are you sure this question is copied properly?


Second Q:

This is definitely C. the whole purpose of the ETC is to pump H+ ions to the IMS so that when the gradient is built up ATP Synthase can shuttle back H+ into the mito converting ADP -> ATP in the process.

EDIT:

Update: (just to confuse you)
By concentration
Outer mitochondrial membrane 50:1 lipid/protein
Inner mitochindrial membrane 15:1 lipid/protein
By mass
Outer mitochondrial membrane 1:1 lipid/protein
Inner membrane 1:3 lipid/protein
So, which did they mean? Anyone? Either way, I still don't know the answer.

Lol. You typed this as I was typing my response. We are definitely on the same page. hahaha.

 

[blastula]

Which of the following statements is true of the outer and inner mitochondrial membranes?

A The outer membrane is mostly lipid and the inner membrane is mostly protein.
B The inner membrane is mostly lipid and the outer membrane is mostly protein.
C The inner and outer membranes are very similar with regard to amount of protein and amount of lipid.
D None of the above.


The ATPase in the inner mitochondrial membrane makes ATP using energy derived directly from

A A high energy phosphorylated metabolic intermediate
B An electron gradient across the inner mitochondrial membrane.
C A proton gradient across the inner mitochondrial membrane
D Glycolysis

Inner membrane has more proteins because they transport NADH and pyruvate inside the matrix. It also has proteins that shuttle H ions to form the gradient which is used by ATPase to make ATP.

1. A
2. C

 

[RSAgator]

I think the first question should ask about the two relative to one another rather than absolutely. The best answer almost anyone could give would be an educated guess. Where'd you get this question?

 

[JoeC]

The answer to question one should be C, I believe. Both membranes will be mostly comprised of lipids studded with proteins, there shouldn't be that much difference between them, then inner membrane has ETC components, the outer will be filled with transporters and the like. No membrane will be mostly protein, so A and B are false.

 

[coffeebythelake]

D, C are correct.

Inner mitochondrial membrane contains about 20% protein.