Conditional cell lock/unlock

I have set up a worksheet where a user would enter "y" in either G16 or O16. These are the only two unlocked cells on the sheet. If "y" is entered in G16 I would like O16 to lock and G27,31,33,36 to unlock. If "y" is entered in O16 I would like G16 to lock and O21,23,27,31,33,36 to unlock. The worksheet is also protected. Can anyone help please.

There may be a flaw in your request, if you were to lock one of the two cells the one cell will always be locked and will never =y

I can live with both O16 and G16 staying unlocked (see worksheet - calculator and data to the right of the calculator).