3.15 Describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

Above, you can see an image of the structure of DNA. It is made up of two coiled strands, known as a sugar phosphate backbone. As the name suggests, it is made up of a sugar and a phosphate (alternating). The base pairs are the 'coding'. It is believed that every living thing has the same base pairs:

• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

Adenine always pairs up with thymine, guanine always pairs up with cytosine. The order in which these are paired in is what makes up the 'coding' of an organism.

(Virtual flashcards on this topic can be found here, or click 'inheritance flashcards' on the right hand side menu)