The two sides of a DNA strand, also known as the "backbone," are composed of alternating sugar and phosphate molecules. The sugar in one strand is called deoxyribose and the other strand is composed of a base, which can be adenine, thymine, guanine, or cytosine. These bases form the "rungs" of the DNA ladder and are held together by hydrogen bonds, which connect the two strands of DNA. The sequence of these bases on one strand determines the complementary sequence of bases on the other strand, which is what allows for DNA replication and the transmission of genetic information.