Locking cells depending on what is entered in another cell

Hi,

I'd like to lock some cells depending on what is put in a particular cell.

As shown by the file attached, if the first column (Amendments) has a "no" in A4, I'd like to lock out cells B4:D4. (The sheet will be protected). If it's a "yes" then the cells are unlocked.

I'd like to then apply this to all subsequent rows (i.e. lock B5:D5 if a "no" in A5 etc.)

Can anyone help?

Have attached a sample file.

Nujwaan