Answer:
The backbone of a DNA strand is a crucial structural element that consists of two alternating components:
1. **Deoxyribose Sugar:** The backbone of DNA is composed of a sugar-phosphate backbone. The sugar molecule involved is called deoxyribose. Deoxyribose is a five-carbon sugar and serves as the "sides" of the DNA ladder-like structure. The deoxyribose sugars are linked together to form a continuous chain.
2. **Phosphate Group:** Alternating with the deoxyribose sugars are phosphate groups. These phosphate groups are bonded to the deoxyribose sugars. They connect one deoxyribose sugar to the next along the length of the DNA strand. The phosphate groups, along with the deoxyribose sugars, provide the structural stability and support for the DNA molecule.
The deoxyribose sugar and the phosphate group together create the "sugar-phosphate backbone" of DNA, and this backbone forms the structural framework to which the nitrogenous bases (adenine, thymine, cytosine, and guanine) are attached. The nitrogenous bases, which are responsible for encoding genetic information, are connected to the deoxyribose sugars and extend inward from the backbone to create the rungs of the DNA double helix. This complementary base pairing between the nitrogenous bases on the two DNA strands forms the genetic code that carries the instructions for life.