Is it right to be put as the last author although I have done the bulk of the work? I am doing my PhD at a research institute, where we have just finished the draft of a 8-hands long paper to be published as a short book with a major editor. I have done the bulk of the work, i.e. at least 80% of the total. However, my coordinator sent me the draft back with the authors reordered by seniority, and I now figure as the last author although my contribution was the largest. I should mention this would be my first publication. Shall I react?
The order of authors is often problematic and thus I guess this question will be closed as duplicate soon.

Anyway, you should discuss this with your coordinator and ask him why he prefers this order. My colleague is working in a similar area than yours and he is usually the first author, but there might be other reasons in your situation.

Even if you are not able (or not willing to) insist on your preferred order, there are other options to emphasize your contribution. For example you could add an "Authors Contribution" section where you can explain in detail who did which part of the work. Footnotes at the author names are a common alternative (e.g. "* These authors contributed equally as main authors" or "¹ AB developed the model ² CD wrote the manuscript"). 

This is not only a question of fairness, but there might also be a formal requirement for your PhD or later research positions like "You have to publish two papers as main author." If that is the case, you should ask your supervisor how to address this issue.