Introductory books on nature sciences behind bioinformatics
As a previous response stated, it is not an absolute requirement that you study biology in order to do bioinformatics.  However, if you wish to have a background understanding of the foundational concepts such as genes, RNA, DNA, etc. then a good introductory biology book should provide everything that you need.   

Molecular biology is not the kind of topic that one can simply dive into the middle of, though. Therefore, in order to understand it, you need to do some introductory reading.   The best book is one that has enough detail without assuming that you wish to become a biologist.

I suggest that you look at Collins Outline of College Biology. Reading chapters 2-5 and 12-15, should give you basic information you desire.  Another choice is Schaum's Outline of Biology, Third Edition, chapters 2-4 and 7-10.   Both books cost less than $20.00 and are easy to understand.  Hope this helps.