Summary
Two antiparallel strands of nucleotides wound into a double helix, held together by base pairing.
In depth
Two antiparallel polynucleotide strands form a right-handed double helix about 2 nm wide with 10 base pairs per turn. A pairs with T through two hydrogen bonds and G pairs with C through three, so GC-rich DNA is more heat stable.
Watson and Crick built the model in 1953 using Rosalind Franklin's X-ray diffraction images and Chargaff's rules (A = T, G = C).
The double helix has a major groove and a minor groove where proteins read base sequences without opening the helix. Complementary base pairing allows each strand to act as a template; Franklin's X-ray diffraction image (Photo 51) revealed the helix. Alternative forms exist: A-DNA in dehydrated conditions and Z-DNA, a left-handed form, in GC-rich stretches.
Chromosomes are circular in prokaryotes and linear in eukaryotes, where DNA wraps around histones to form nucleosomes, each with about 147 base pairs wound around eight histones. Melting temperature rises with GC content because of three hydrogen bonds.
Key idea: structure explains function: the stable backbone protects information, and base pairs allow copying.
Frequently asked questions
What is DNA Structure?
Two antiparallel strands of nucleotides wound into a double helix, held together by base pairing.
Which area of biology covers DNA Structure, and how advanced is it?
DNA Structure is one of the 51 topics in Biomolecules & Biochemistry. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Nucleic Acids, Denaturation, Secondary Structure.
Why does DNA Structure matter?
The complementary strands explain how DNA is copied accurately.
What should I learn before DNA Structure?
Work through the Beginner topics in Biomolecules & Biochemistry first, such as Water Properties, Carbon Chemistry, Carbohydrates, then return to DNA Structure. Intermediate topics assume the Beginner vocabulary.
What topics are related to DNA Structure?
The closest topics to DNA Structure are Nucleic Acids, Denaturation, Secondary Structure, Nucleotides. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand DNA Structure?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for DNA Structure. To practise the whole of Biomolecules & Biochemistry, use the Biomolecules & Biochemistry quiz.
How is DNA Structure different from Nucleic Acids?
DNA Structure: Two antiparallel strands of nucleotides wound into a double helix, held together by base pairing. Nucleic Acids: DNA and RNA, polymers of nucleotides that store and transmit genetic information. Read both side by side and note what each one explains.
How should I study DNA Structure step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Nucleic Acids and explain the difference aloud. Finally, take the Biomolecules & Biochemistry quiz and come back to this page for any question you miss.