In my western blot today I noticed that only 5 out of 7 - 50 kda bands of the marker were visible. In addition, in the ponceau I saw bands only until the 50kda marker.
So, protiens that are smaller than 50kd were not visible.
Markers have degraded unless you are sure that all of the bands are visible on gel.
Membrane pore size is high and is not capable of resolving lower molecular weight proteins. So when you are doing the transfer, these markers are passing through the membrane and thus you’re not able to visualize.
SDS PAGE with regular SDS Glycine Tris resolving buffer has poor resolution in the LMW protein range and your markers below 50kDa are falling in the same range. I suggest you proceed with Tricine Buffer or change the pH of resolving buffer to 9.2 that will be able to resolve proteins in LMW range effectively.