* G binds to C (by 3 hydrogen bonds) these two bases are present in DNA and RNA.
The hydrogen bonds between the bases of one nucleic acid strand and the bases of another strand maintain the 2 strands united (This is the definition of the pairing).
A purine always binds to a pyrimidine on the other strand (so their numbers are equal).
The hemoglobin molecule has four binding sites for oxygen molecules: the iron atoms in the four heme groups. Thus, each Hb tetramer can bind four oxygen molecules.
