Why do you need to lock these tables? What is the problem you are trying to solve?
In Oracle, it is exceptionally rare that you actually need to acquire an explicit lock on a table. And in Oracle, it is impossible to lock a table in a way that prevents other sessions from reading the data in the table. It does not appear that you'll be able to map this directly into Oracle because you cannot block readers.
The lock table syntax in Oracle is relatively similar to the syntax in MySQL. You could, for example
LOCK TABLE alpha IN row exclusive mode;
But it is not clear whether this is going to really solve whatever problem you're facing.