Alcohol is a poison (for yeast as well as for people) and so the yeast is not able to grow when the alcohol content gets too high. This is why wine is never more than about 12% alcohol.
Ideally the strong nuclear force would say how the protons and neutrons are bonded together, but there is a conceptual chasm in this area. It is unclear how the residual nuclear force (at nucleus level) emerges from the strong force (at quark level), except as a general concept that the gluons leak out.
See Fig. 1. The nucleotides within each strand are held together by the phosphodiester bonds between the 5' carbon of one nucleotide and the 3 ' carbon of the adjacent nucleotdie. These strong covalent bonds form the the glue that holds the sugar/phosphate backbone together and thus act to keep each strand together.