Asked by Sam
why is the structure of DNA described as a double helix
All Answers 1
Answered by
GPT-5 mini
AI
Because DNA is made of two long nucleotide strands that are wound around the same central axis in a spiral, like a twisted ladder. That geometry—two strands forming a spiral—fits the phrase “double helix.” More specifically:
- Two complementary polynucleotide strands run in opposite directions (antiparallel). Each strand has a sugar‑phosphate backbone on the outside and nitrogenous bases on the inside.
- Bases on opposite strands pair specifically (A with T, C with G) via hydrogen bonds, which holds the two strands together like rungs of a ladder.
- The strands are twisted into a helical (spiral) shape so the hydrophobic bases are tucked into the interior away from water while the charged, hydrophilic sugar‑phosphate backbone faces the solvent. This arrangement is energetically favorable and stabilizes the molecule.
- Base stacking (π–π interactions between adjacent bases) and interactions with ions and water further stabilize the helix and give it a regular geometry: about 2 nm in diameter, ~0.34 nm between stacked bases, and ~10 base pairs per turn in the common B‑form.
The double‑helix structure was deduced from X‑ray diffraction data (notably Rosalind Franklin’s patterns) and modeled by Watson and Crick in 1953. That structure explains DNA’s key properties—stable information storage, precise base‑pairing for replication, and grooves (major and minor) that allow proteins to read and copy the genetic code—so “double helix” both describes its shape and reflects why that shape works biologically.
- Two complementary polynucleotide strands run in opposite directions (antiparallel). Each strand has a sugar‑phosphate backbone on the outside and nitrogenous bases on the inside.
- Bases on opposite strands pair specifically (A with T, C with G) via hydrogen bonds, which holds the two strands together like rungs of a ladder.
- The strands are twisted into a helical (spiral) shape so the hydrophobic bases are tucked into the interior away from water while the charged, hydrophilic sugar‑phosphate backbone faces the solvent. This arrangement is energetically favorable and stabilizes the molecule.
- Base stacking (π–π interactions between adjacent bases) and interactions with ions and water further stabilize the helix and give it a regular geometry: about 2 nm in diameter, ~0.34 nm between stacked bases, and ~10 base pairs per turn in the common B‑form.
The double‑helix structure was deduced from X‑ray diffraction data (notably Rosalind Franklin’s patterns) and modeled by Watson and Crick in 1953. That structure explains DNA’s key properties—stable information storage, precise base‑pairing for replication, and grooves (major and minor) that allow proteins to read and copy the genetic code—so “double helix” both describes its shape and reflects why that shape works biologically.
Submit Your Answer
We prioritize human answers over AI answers.
If you are human, and you can answer this question, please submit your answer.