AQA GCSE Biology Paper 2 Complete Practice Exam 2026

The structure of DNA is composed of two polymer chains that form a double helix. This double helix is a specific shape that resembles a twisted ladder, where the sides of the ladder are made up of alternating sugar (deoxyribose) and phosphate groups, and the rungs consist of pairs of nitrogenous bases (adenine with thymine and cytosine with guanine). The double helical structure is essential for the function of DNA, as it allows for the accurate replication and encoding of genetic information. The base pairing ensures that the genetic code can be reliably copied during cell division.

In contrast, a single chain of nucleotides would not provide the stability required for the structure to maintain its integrity for encoding genetic information. A triple helix configuration is not the standard form of DNA and is generally associated with some complex forms of RNA or specific DNA structures under special conditions. Lastly, linear chains of glucose molecules refer to polysaccharides and have no relation to the nucleotide structure of DNA.