This question (and variants very similar to it) have been asked many times on this site. I'd recommend searching for some of those questions.

In short, a solid foundation of molecular biology, genetics, and experimental design will be helpful pretty much regardless of what you do later. A basic grasp of stats will not go wasted either, though most Masters programs should cover that as well.

So if you don't have of a good understanding of what a gene, DNA, RNA, and proteins really are, courses that teach that will be very useful.

I think those considering a career in bioinformatics may be helped by making a choice between these two options:

• The analysis of biological molecules using computers and statistical techniques
• The science of developing and utilizing computer databases and algorithms to accelerate and enhance biological research

If the second option is more appealing, a career in computational biology, or a supporting career in bioinformatics, may be better choices.

There are many definitions of bioinformatics, and I recommend the following paper to my students:

http://archive.gersteinlab.org/papers/e-print/whatis-mim/text.pdf

A short version of their definition would be something like this: Bioinformatics studies macromolecules by applying “informatics” techniques to understand and organize the information on a large scale.

A key thing here is that bioinformatics works with biological macromolecules, so understanding them is essential. At a minimum that means a couple of biochemistry and molecular biology classes. Understanding how these molecules work together and how they are regulated requires a molecular genetic class. Beyond that we get into specifics depending on individual interests. To study these molecules directly, one would probably need a course in macromolecular methods. Someone studying proteins will probably need a course in protein structure. If a person has no interest in bench work, getting stronger foundation in statistics and algorithms could be beneficial. A proper bioinformatics course would probably be useful to tie everything together.

If you can, find a professor to do bioinformatics research with. That’s the best way to learn in my opinion.