Grade Saved


Your grade

The structure of DNA





James Watson and Francis Crick worked out the structure of DNA in 1953.

-> X-ray diffraction photograph of DNA

By using data from other scientists they were able to build a model of DNA.

The X-ray data they used showed that DNA consists of two strands coiled into a double helix.





Base pairs

Each strand of DNA is made of chemicals called bases.

Note that these are different to bases in relation to acids and alkalis in chemistry.

There are four different bases in DNA:

- thymine, T

- adenine, A

- guanine, G

- cytosine, C [2]

Complementary base pairing

There are chemical cross-links between the two strands in DNA, formed by pairs of bases.

They always pair up in a particular way, called Complementary base pairing

Two examples are:

- thymine pairs with adenine (T–A)

- guanine pairs with cytosine (G–C) [3]

You may be interested in

© 2017