If your puppy is chasing and biting your cat, keep him tethered to you (on a leash) or crated at all times. That way you can redirect immediately when he tries to bother the cat. He needs to learn that he cannot ever chase or bite the cat. I cannot emphasize this enough--there are several members on here whose cats have been killed by their dogs.
Also, you can but dog gates that have a little gate at the bottom that a cat can get through. I would also be sure to crate your puppy for some time when you're home so that you can spend time with your cat.
It is up to you to protect your cat and that may mean limiting your puppies freedom for quite some time!
Ruth & the 4 Legged Rescue Gang
Rafi the malaroo
Gio & Varda, the krazy kittens
....In my heart: