Which of the following correctly describes the structure of DNA?

The correct choice describes DNA as a double helix made of polynucleotide chains. DNA (deoxyribonucleic acid) is a molecule composed of two strands that twist around each other, forming a helical shape known as a double helix. Each strand is made up of a long chain of nucleotides, which are the building blocks of DNA. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base. The double-stranded structure allows for the complementary pairing of bases (adenine with thymine, and cytosine with guanine), which is crucial for the replication and transmission of genetic information.

The other options mischaracterize DNA's structure in various ways. Suggesting it is single-stranded with ribose sugar would describe RNA, not DNA, as DNA contains deoxyribose rather than ribose. Describing DNA as a complex protein structure is inaccurate because while proteins can interact with DNA, DNA itself is not a protein. Lastly, stating that DNA has a short and circular structure might describe certain bacterial DNA (like plasmids), but generally, eukaryotic DNA is organized into long, linear chromosomes. Thus, the choice highlighting DNA as a