Oligo Molarity - (Sep/03/2019 )
Hello! I understand this may be a very simple question in comparison to many on here, but alas I am still having trouble with it. I am trying to make ensure I have the correct concentration of Oligo-dt primers for a reaction. I am needing 10μM of Oligo-dt but the only information I have is 0.4μg/μL. Am I correct in that this isn't enough information to determine molarity? The product is through Qiagen and I have looked through their handbook and all the ordering information, but have not found anything on the morality or on Oligo-dt's molecular weight. Maybe I am just not understanding? Sorry if this is unbearably simple, in my defense I am still a student.
I think you may be confused here. To me it looks like you have a Qiagen system for capturing mRNA and cDNA synthesis via an immobilized oligo-dT. If this is the case, then they have supplied it at the concentration needed for the kit, and you need to use the capture plates/strip-tubes to use this effectively. It is not designed to make cDNA in an independent reaction (though it probably could).
They have not supplied enough information to calculate the molarity of the solution.
To determine the molarity you would need to know how long an oligomer you have. Most likely this is between 12 and 22 bases long, and is probably a mixture of lengths, though they may have HPLC or gel purified it to get it into a conjugated form for the immobilization. From this you could work out the molecular mass for each and then use that to determine the concentration in uM.
However, you probably don't need to do this - most reactions for cDNA synthesis use around 0.5 ug of oligo-dT per ug of polyA-mRNA or 0.5 ug with less than 5 ug of total RNA.