And seven of these 20 different amino acids have readily ionizable side chain groups. And what that means is the side chains can basically lose or gain an age atom at a specific PH value. And so for a specific amino acid that is ionizable at certain PH values, the side chain will have a charge. But at other PH values, the side chain will be neutral. Now, to see exactly what we mean by this, let's take a look at the following two examples. So these are the two out of the seven ionizable amino acids.