AAMC Section Bank Question

[holdmystethoscope]

Hi I am having trouble with these following question
A description of the structures of four proteins is shown bellow


Protein Description
Protein 1 32 kDa monomer
Protein 2 Disulfide-linked homodimer comprised of 19 kDa monomers
Protein 3 Homotrimer comprised of 25 kDa monomers
Protein 4 Homodimer comprised of 38 kDa monomers

Which protein has the highest electrophoretic mobility in SDS-PAGE under non-reducing conditions? (Note: There are no disulfide interactions unless stated in the table.)

So the answer is protein 3 because it's 25KDA total which is the lowest compared to other three proteins. It's question 64 in section bank for chem if you have access. My question is how the total mass of protein 3 won't be 25*4 = 100 since it's homotrimer which i thought means four monomers.

Thanks.

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[aalamruad]

SDS is a strong detergent, and it breaks subunits apart into primary structures. The 25 kDa monomers will move as individual, small units, which are smaller than any other single polypeptide chain in question.

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[To be MD]

SDS is a strong detergent, and it breaks subunits apart into primary structures. The 25 kDa monomers will move as individual, small units, which are smaller than any other single polypeptide chain in question.

Sent from my HTC6525LVW using SDN mobile

Thank you

 

[Wolfpack93]

Hi I am having trouble with these following question
A description of the structures of four proteins is shown bellow


Protein Description
Protein 1 32 kDa monomer
Protein 2 Disulfide-linked homodimer comprised of 19 kDa monomers
Protein 3 Homotrimer comprised of 25 kDa monomers
Protein 4 Homodimer comprised of 38 kDa monomers

Which protein has the highest electrophoretic mobility in SDS-PAGE under non-reducing conditions? (Note: There are no disulfide interactions unless stated in the table.)

So the answer is protein 3 because it's 25KDA total which is the lowest compared to other three proteins. It's question 64 in section bank for chem if you have access. My question is how the total mass of protein 3 won't be 25*4 = 100 since it's homotrimer which i thought means four monomers.

Thanks.

Also homoTRIMER would be 25x3 not 4. Homotetramer would be 25x4. Not that it matters since this is SDS, but make sure you don't mix those up haha

 

[DaAlienist]

moved to proper thread

 

[scrubsalublub]

SDS-PAGE without reducing agents will not break disulfide bonds. That's why they specify "without reducing agents" in SDS-PAGE, so that's why Protein 2 would b3 2x(19 kDa)= 38 kDa and the largest (same as Protein 4).