Modern molecular biology provides a rich source of challenging machine learning problems.
This tutorial chapter aims to provide the necessary biological background knowledge
required to communicate with biologists and to understand and properly formalize
a number of most interesting problems in this application domain.
The largest part of the chapter (its first section)
is devoted to the cell as the basic unit of life.
Four aspects of cells are reviewed in sequence:
(1) the molecules that cells make use of (above all, proteins, RNA, and DNA);
(2) the spatial organization of cells (``compartmentalization'');
(3) the way cells produce proteins (``protein expression''); and
(4) cellular communication and evolution (of cells and organisms).
In the second section, an overview is provided of the most frequent
measurement technologies, data types, and data sources.
Finally, important open problems in the analysis of these data
(bioinformatics challenges) are briefly outlined.