So instead of synthesizing glutamate at the 6th position, we synthesize valine at that 6th position. And the problem is the properties of these two amino acids is different. The properties of this one is that of a polar molecule. But valine is a non polar molecule, and that will create the difference, as we'll see in just a moment. So what causes that normal shape of hemoglobin? Well, it turns out that there is a genetic error that leads to a single amino acid substitution in the beta chains of the hemoglobin molecules.