Eric Lander's incredible 'Introduction to Biology - The Secret of Life' was my first step away from data analysis for online marketing clients (which I didn't love) to bioinformatics (which I do very much love)
I'd like to second this. I had only slight interest in Biology but got completely hooked into the course because the teacher makes things so plausible and exciting. I wish one could do bioinformatics remotely, I'd seriously change careers ;)
https://www.edx.org/course/introduction-biology-secret-life-...
A Fantastic course from a legendary educator.