Hello Ayen,
I am a medical student and have utilized memory palaces extensively throughout my studies. As to how it relates to your classes, obviously biology and even chemistry are right in line with my subjects, gov not so much but I think it would translate pretty easily.
Disclaimer: I have worked with mnemonic techniques for over 3 years now, so I have a little jump on you, experience-wise.
Nonetheless, I’ll give you what I have learned works best for me.
First off, I have plenty of memory palaces (which I think is key and very easy to accumulate - there are great threads on this site in reference to this topic). This allows me to have a greater amount of time/lectures before I need to re-use a palace. My best palaces come from friends’ houses I’ve visited regularly, restaurants I’m really familiar with, even stores I have shopped in a lot, and yards or parks (outdoor areas) are actually by far my best because they feel very uninhibited to me, but really just any place I can visualize myself walking around in. I haven’t delved into movies or video games, but it sounds like those are great options if they are detailed enough in your mind.
Within the palaces, for this technique, I don’t have a strict passage throughout; I do have general idea of the directions I want to go. The reason I don’t have a strict passage is because in these lectures you never know what information you might have that needs to be plugged in at the next loci. For instance, if I have a simple definition then it’s fine to put that on a loci that is small and maybe doesn’t have the space around it that I would like to have if the next piece of information is a list of symptoms for a disease — that would need a loci with more room to visualize more data.
I use one palace for each 1 hour lecture and I have had no problems whatsoever, even with how dense our lectures can get; however, the palaces I’m using have, on average, around 40-50 loci so if your palaces don’t have this many loci, you may need to use one or two more per lecture. The next thing to know is that we also have multiple “subjects” going on at once (for instance, biochem, physiology, histology, etc) so this system has worked in this respect as well. All that I do is keep a word document on my computer (a sheet of paper would work just as well) and keep track of which palaces I use for each lecture of which subject. I have tried the technique of using restaurants for this subject, friends’ houses for this one, etc., but I haven’t noticed a difference in just picking and choosing whichever palace I want to use at that time — after all, some palaces I can utilize better than with others, so for harder material I use my stronger palaces.
In reference to the information itself, I first like to go through the power points (or maybe book chapters in your case) and as I go through just jot down each topic I can separate out. This is not taking notes. In a chemistry lecture, it might be each periodic table element you were focusing on that day, or maybe each chemical reaction discussed. In bio, maybe it’s each bacteria discussed, or each species, or both—whatever is in that particular lecture. On some days there might be 3-7 and I would just put those in separate spaces (1 per main room, or one per main space - front of house, middle of house, back of house, despite the number of rooms in that division of space); on other lectures, there might be 20-30, maybe more, and it doesn’t seem like they can be divided up other than just each piece of information. In this case, I just pretty much go loci to loci. Going back to when I said there may be 3-7, obviously there will be a lot of information inside of these main topics, so that is when you will just make use of the loci in and around those main spaces you divided up, but it will allow you to easily go straight to that room/space and know that information is all connected somehow. The reason I do this beforehand, and not just going through and plugging in the data as you study, is because it’s nice to know just how many loci you’ll use so you know how far you can spread them out. As an aside, I also use the major system when needing to plug in numbers, and other techniques when needed as well — i.e. if it’s a chart that isn’t somehow divisible or it’s easier to learn in chart form this would require a different system that you can find elsewhere on this site.
Plugging in the specific information is then pretty easy. I make a strong association between the piece of material and the loci and spend the majority of the time doing that, because that is really the crux the technique and without that association I could never recall the piece of information when it comes up on the exam. As for linking the specific loci, I use the journey that I walk as the link and can see myself walking from loci to loci, otherwise if I can’t, I know that I haven’t really locked in the material; so I don’t really spend time linking the 2 subsequent loci other than that.
This is the gist of how I have utilized the system. You can really only get an actual sense of it once you’ve tried it, as with many things. I really feel that once you have enough palaces where you have really locked in good strong loci, this method will work well. At lease, it has for me 
-[sorry so long!]-