Question

what is the base sequence of 16s small ribosomal unit of rRNA? purine or pyrimidine?

Answer 1

The sequence of the 16s small ribosomal subunit contains all four nucleotides found in RNA molecules - A, U, G and C. Of those, adenine (A) and guanine (G) are both purines; cytosine (C) and uracil (U) are both pyrimidines, so it contains both.

The sequence itself is something you would have to look up. And it will depend on what species you are looking at. Though ribosomal subunits are among the most conserved macromolecules - even the smallest changes by mutation in molecules that are this essential tend to be lethal, so very little sequence divergence occurs in ribosomal subunits as compared to most other macromolecules over time - they do differ depending on species.

The National Centre for Biotechnology Information - www.ncbi.nlm.nih.gov/‎ - is the sequence repository database where you will find that sequence information for whatever species you are looking for, provided that species' rRNA subunit has actually been sequenced.