There is like one bass riff all along the song, going as the following (for 
perfect timing check the song, it's very simple):

G:|--------------------|-----------------||
D:|--------------------|-----------------||
A:|--------1-----1h3p1-|-----------------||
E:|-3------------------|-1--------3------||

If you want to play the melody for making the bass more interesting, it goes like that:

G:|------------------|-------------------||
D:|---5--3-----------|---3--1--5~--------||
A:|---------5~-------|-------------------||
E:|-3----------------|-1-----------------||

h - hammer on,
p - pull off,
~ - vibrato.

Thank you.