Can you describe zwitterions?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Amino acids exist as zwitterions when they are at their isoelectric point (also known as the pI value).  This is the pH at which the amino acid has both a negative charge (on the carboxylate side of the molecule) and a positive charge (on the amino side of the molecule).  Overall, it is a a neutral molecule, but it has both charges present within the structure.  The charges are always +1 and -1.

This is only true for amino acids at that particular pH.  When the pH changes, one of the ions goes away.  At low pH values, there is an excess of H+ ions present resulting in the protonation of the negative ion so the amino acid has a positive charges.  At high pH values, there is an excess of OH- ions present resulting in removal of the proton from the carboxylic acid side and as a result, we end up with a negative ion.

See eNotes Ad-Free

Start your 48-hour free trial to get access to more than 30,000 additional guides and more than 350,000 Homework Help questions answered by our experts.

Get 48 Hours Free Access
Approved by eNotes Editorial