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. Remember, we have two beta chains in a single hemoglobin molecules, and both of those chains will have that abnormality. So glutamate at the 6th position is substituted to the valley in that same position. So in normal hemoglobin, glutamate six is a polar molecule, and normally it points to the surface, to the outside of the blood plasma.