Does SQL Server Put A Shared Lock On All Tables Within A Transaction?

Would table1, table2 and table3 in code below, be locked with a shared lock from start of transaction to the end of transaction Or they would only be locked for the duration of  their update, or insert statements and not for the entire transaction? Default isolation level is in effect in SQL Server.

 begin tran
   update table1 set column1 = 100
   if @ERROR = 0
     begin
       declare @stat int
       set @stat = (select stat from table2 where  employeeid = 10)
      insert into table3 (col1, col2) values (@stat , 325)
      if @@ERROR = 0
         commit tran
      else
         rollback tran
     end
   else
      roll back tran