How to setup a domain name for my website hosted on ubuntu?

I have created a django website and instead purchasing a hosting service, i have hosted the website on my own PC having public IP. Hence now i can access my website through my IP address. Next step is to assign a domain name to my IP and hence everyone on internet can access my website through the domain name instead of IP. I know, there is a lot of sites for purchase a domain name but i don't want to purchase. Is it possible to run a dns server on my system or anyother system connected to internet and set up a domain name for my website so that it can be accessed on internet?