Quick Question regarding amino acids

[raca1111]

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Hey guys, here's my question!

If you have a transmembrane protein that contains basic amino acids on the extracellular side of the cell at pH 7, will the transmembrane be more likely to attract negatively charged particles and vice versa for acidic amino acids?
My thinking was that at a pH of 7 the basic amino acids would be positively charged (protonated) and would have a stronger affinity for negatively charged particles outside the cell. Is this right thinking or do I have this completely wrong?

THANKS

 

[BerkReviewTeach]

You have it right! Basic AAs carry a positive charge at pH = 7 (full (+)s on Lys and Arg, and a partial-(+) on His), so they will attract negatively charged residues.

But keep in mind that there must be charge balance, so that channel must have a negatively charged species somewhere to offset the (+)-charges of the basic side groups.

 

[raca1111]

okay thank you so much!

 

[jimmypod]

Yeah! If you are curious, there is also this interesting phenomenon seen in alpha helixes where amino acids near N-terminus (which contains a positively charged amino group) have an affinity for negative R groups while amino acids near C terminus (which contains the negatively charged carboxyl group) have an affinity for positive R groups. Thus, if all other factors are equal, then replacing a negative R groups with a positive R group on the N-terminus side of the amino acid will effectively destabilize the secondary structure a lot more than you would normally think.

Just an interesting correlation with your question, though I don't suppose I helped answer anything you were looking for hahaha