I think for most schools, they start with biochem because it's kind of the odd-ball class and gives you a nice foundation for which the other classes build. By that, I mean after this course, everything is grouped into organ systems. Knowing the biochemical pathway of gluconeogenesis is important because once you get to the GI system, they will talk about how the liver is important in this and if you haven't seen the actual pathway, then you won't have a clue how everything relates. At least that's the way it is a most med schools I know.