Now, let's move on to the two acidic amino acids, aspartate and glutamate. So what do we mean by acidic amino acids? Well, acidic simply means that the side chain groups will have a full negative charge at the normal physiological PH, and that's because the PKA value of the side chains will be relatively low, will be below seven. So if we examine the PKA value of the side chain groups in Aspartate and Glutamate, the PKA value is 4.1. And what that means is, below 4.1, these groups are very likely to be protonated. But above 4.1, these groups are very likely to be deprotonated.