Newbie with database design qiuestion

Hi all,

I did an SQL course at University about 20 years before, and am currently writing a database app. I have a problem with the design.

I have a table PEPTIDES with (among others) a column weight

I have a table TAGS

Now a peptide (e.g. MADGHDLPTVASQLTNASRGMQAL) can have different tags (like phosphate groups added, or a lipid, or ...), and different numbers of tags (could be 0, 1, 2, etc phosphates, depending on how many S and T a peptide has).

Adding a tag of course changes a peptides weight.

So a peptide can have no tags, a few, or many, and that means it can have many different weights. But where do I store all these weights? I would end up with hundreds of columns for all the different combinations, so that is no solution.

Any idea on how I could proceed?

Thanks

Markus