DNA (Deoxyribose Nucleic Acid) is a molecule that forms our genetic material. It is used to store instructions that allow a cell to function and to generate new cells and organisms. These instructions are encoded by long sequences of just four different subunits arranged in different combinations. These subunits are known as nucleotides – Adenine (symbolized as “A”), Thymine (“T”), Guanine (“G”) and Cytosine (“C”) – and these nucleotides interact with one another in a way gives DNA its characteristic structure.

Watch James Watson, one of the men credited with discovering the structure of DNA, describe how he and Francis Crick arranged the nucleotides to match up Adenine with Thymine, and Cytosine with Guanine.  This discovery of nucleotide pairing was the breakthrough needed to finally solve the problem they had been grappling with:

The bonds highlighted in the video are known as “hydrogen bonds”. On their own, these are very weak bonds –  you can think of them as very small magnets attracting each other at a distance. In a long DNA molecule however, when there are many such bonds, they ensure a very strong attachment of the two DNA strands that make up the “double helix”.

(You can read James Watson’s personal account of the discovery in his book “The Double Helix.”)

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Comprehension Question