Should differential backup be followed by transaction log backup

Hello,

We're using sql 2005 enterprise sp2 with db(70 -80 GB) using full recovery mode and recently we want to apply full backup(once a week) and differential database backup(once a day). Is it compulsory to apply transaction log backup also? If yes is it possible to set transaction log backup once a day instead of hourly basis? Thx a lot

Best regards,

Wallace