- In I/GCSE Biology, a DNA molecule has two strands coiled together in the shape of a double helix.
- The stands are held together by bases. There are four different bases:
- The bases are always paired:
- A - T
- C - G
- The base pairs are joined together by weak hydrogen bonds.
- A gene is a section of DNA, and the sequence of bases in a gene code for a specific protein.
The discovery of DNA
- Rosalind Franklin and Maurice Wilkins worked out that DNA had a helical structure by directing beams of x-rays onto crystallised DNA.
- James Watson and Francis Crick used these ideas, along with the knowledge that the amount of adenine and guanine matched the amount of thymine and cytosine, to make a model of the DNA molecule.