What is the structure of DNA?
Short answer
DNA is a double helix: two strands twisted around each other. Each strand is a chain of nucleotides, and each nucleotide has a sugar, a phosphate and one of four bases: A, T, C or G. The two strands are held together by complementary base pairs, A with T and C with G. The order of bases is the genetic code.
Step by step
- Nucleotide: sugar (deoxyribose), phosphate group and a base.
- Sugar and phosphate alternate to form the backbone of each strand.
- Bases pair across the strands: adenine with thymine, cytosine with guanine.
- A gene is a section of DNA that codes for a particular protein.
- Three bases code for one amino acid.
Worked example
Find the complementary strand
- Strand: A T G C C A
- Pairs: A-T, T-A, G-C, C-G, C-G, A-T
- Complementary strand: T A C G G T
Common mistakes
- Pairing A with G or C with T.
- Confusing a gene with a chromosome. A chromosome is a long DNA molecule carrying many genes.
- Calling DNA a protein. It is a nucleic acid that codes for proteins.
Useful for:GCSEA LevelWAECMatricBac
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