Concept preview

What you will be able to do

1. 01Describe the structure of a nucleotide and how nucleotides build a nucleic-acid strand.
2. 02Compare DNA and RNA in sugar, bases and number of strands.
3. 03Explain complementary base pairing and the double helix, and how they allow copying.
4. 04Describe ATP's structure and its role as the cell's energy currency through the ADP-ATP cycle.

The final family of biological macromolecules, the nucleic acids, does something no other molecule can: it stores and transmits the information needed to build and run a living thing. There are two kinds. DNA (deoxyribonucleic acid) is the permanent library of genetic instructions kept in the cell's nucleus, and RNA (ribonucleic acid) is the working copy that carries those instructions out to be used. Both are long polymers built from monomers called nucleotides, and, remarkably, the very same chemical alphabet that stores your genes also underlies the molecule that powers your cells. In this topic we look at how nucleotides are built, how DNA and RNA differ, how the famous double helix holds information, and how a close relative of these molecules, ATP, serves as the energy currency of every living cell.