Can I remove an interior wall which supports a post under the roof ridge?
It is highly highly likely that not only is that wall load bearing but it is a crucial loading bearing wall in the house.  

Without a lot more pictures and plans I can give you a best guess:


Do not remove the 2x4 in the attic.  I doubt there is much load (there shouldn't be) on it but I bet it was added to strengthen the horizontal forces.
It looks like the two kitchen walls next to the living room are fulfilling the load across the house.  The gap looks like what a decent size doorway would be.  Also the fact that one is a few feet in just looks like a design element.  I would think that those few feet are still within the base for holding the load across the path of the "red" beam.
Which means most likely an architect will suggest running a header across bottom wall all the way across the house - on the same plane not the current plane a few feet away.  This is a considerable distance (from the looks of it) so it will be a big big piece of wood or an i-beam.  
You can certainly hide the whole header, but this install will cost you a lot more in either work or money or both.  Or you can integrate part with existing wall and maybe have a post on the outside wall side.  Throw a faux wood cap over the ibeam and the install might be just 2-3k.  


Just understand there is a very very small chance you could just knock the wall down.  There is a great chance that if you did you would see issues almost immediately as there is nothing close to this wall and it hold the perpendicular run on it.   This is something that you will have to have an architect look at.  Even if you DIY you will need plans for permits signed off by someone the city inspector trusts.  You knock down this wall and put up a header... don't plan on selling your house without an inspector noticing it and don't plan on your insurance company helping if there are problems.