couple bio questions...

[mj6969]

Cytochrome c is a protein found at the inner mitochondrial membrane, where it is one of the components of the electron transport chain. The protein can be removed from the membrane rather easily using high salt concentrations. Cytochrome c must be

A An integral membrane protein
B A peripheral membrane protein
C A lipid-anchored membrane protein
D A cytoplasmic protein

The biological significance of the freeze-fracture technique is

A It allows us to view particles in the membrane that span the lipid bilayer, or at least extend halfway into the bilayer.
B It allows us to determine whether a membrane lipid is polar, nonpolar, or amphipathic.
C It allows us to characterize the role and function of membrane-associated proteins.
D It allows us to determine which membrane-associated proteins are affiliated with carbohydrates.

A hydropathy plot shows a protein with a membrane-spanning domain. The membrane spanning portion of this protein has a hydrophobicity index in the positive region of the delta G on the y-axis. Why do membrane-spanning domains have positive delta G values?

A Because it would take an input of energy to force these polar amino acids into the lipid regions of the membrane bilayer.
B Because it would take ATP to make these proteins undergo their reactions.
C Because it would take an input of energy to force these nonpolar amino acids into an aqueous solution.
D Because these proteins are at equilibrium.

---

Members don't see this ad.

 

[RSAgator]

1) Not sure but I'd say B because I believe peripheral membrane proteins are loosely bonded by electrostastic interactions, so I'm guessing that a salt would disrupt those interactions releasing the protein.


2) This seems way beyond the scope of the MCAT. The only place I think i've ever seen freeze-fracturing mentioned was in some research papers on liposome membranes. I would say D because I'm pretty sure it takes an image of the membrane surface.

3) I would say C. Again seems beyond the scope of the MCAT. Can't be A because something membrane spanning is non-polar (hydrophillic part of the phospholipid) so it wouldn't make sense that something polar is in there. B doesn't seem to have anything to do with hydropathy, and it doesn't seem to answer the question. D is wrong because at equlibrium delta g is 0.

where are these questions from?

 

[blastula]

1. B

It's not C or D since it is in the mitochondria. Not A because Na conc would not affect integral proteins. Unless this was part of a passage this is beyond the scope of the MCAT. ETC proteins within the scope are all integral and knowing that might be a stretch.

 

[RSAgator]

1. B

It's not C or D since it is in the mitochondria. Not A because Na conc would not affect integral proteins. Unless this was part of a passage this is beyond the scope of the MCAT. ETC proteins within the scope are all integral and knowing that might be a stretch.

to elaborate further, the only places ions come in contact with integral proteins would be the hydrophilic domains which must be polar, like the ions, in order to be on the aqeueous side of the membrane, so it doesn't make sense that ions would disrupt these proteins enough to remove them.

You're wrong to rule out C simply because it's in the mitochondria. Complex 2 is part of the electron transport chain and I believe it is a lipid anchored membrane protein.

 

[JoeC]

1. B - Definitely.

2. D - According to this site: http://www.biochem.northwestern.edu...initions/Def-F/freeze-fracture_technique.html

3. C - Definitely.

 

[blastula]

to elaborate further, the only places ions come in contact with integral proteins would be the hydrophilic domains which must be polar, like the ions, in order to be on the aqeueous side of the membrane, so it doesn't make sense that ions would disrupt these proteins enough to remove them.

You're wrong to rule out C simply because it's in the mitochondria. Complex 2 is part of the electron transport chain and I believe it is a lipid anchored membrane protein.

There are no lipid anchored proteins in ETC. Complex II is a surface protein. Complex I,III, and IV are integral. C can be eliminated because of ETC. Way beyond the scope...

 

[spicedmanna]

This forum is not for homework help. Closing...