Final answer:
The alpha 3 domain is found in the MHC Class I molecules.
Step-by-step explanation:
The alpha 3 domain can be found in the MHC Class I molecules. MHC Class I molecules are transmembrane glycoproteins that consist of a longer alpha protein chain and a smaller beta2 microglobulin protein. The alpha chain of the MHC Class I molecule is divided into three separate domains: alpha1, alpha2, and alpha3.